,,the ,,boy',s ,,playbook ,,of ,,science3 ,,including ,,the ,various ,manipulations and ,arrangements ,,of ,,chemical ,,and ,,philosophical ,,apparatus ,,required ,,for ,,the ,,successful ,,performance ,,of ,,scientific ,,experiments4 ,,in ,,illustration ,,of ,,the ,,elementary ,,branches ,,of ,,chemistry ,,and ,,natural ,,philosophy4 ,,by ,,john ,,henry ,,pepper1 ,f4,c4,s41 ,a4 ,,inst4 ,c4,e42 ,,late ,,professor ,,of ,,chemistry ,,at ,,the ,,royal ,,polytechnic1 ,,etc4 ,,etc4 ,,author ,,of ,,the ,,playbook ,,of ,,metals4 ,,new ,,edition4 ,illustrated with #dgj ,engravings1 ,,chiefly ,,executed ,,from ,,the ,,author',s ,,sketches1 ,,by ,h4 ,g4 ,,hine4 ,,london3 ,,george ,,routledge ,,and ,,sons1 ,,the ,,broadway1 ,,ludgate4 ,,new ,,york3 #daf1 ,,broome ,,street4 #ahfi4 ,,london4 ,,savill1 ,,edwards ,,and ,,co41 ,,printers1 ,,chandos ,,street4 ,,covent ,,garden4 ,illustration3 ,wheatstone's telephonic concert at the ,polytechnic1 in which the sounds and vibrations pass inaudible through an intermediate hall1 and are reproduced in the lecture-room unchanged in their qualities and intensities4 ,frontispiece4 ,,to ,,professor ,,lyon ,,playfair1 ,c4,b41 ,f4,r4,s4 ,,professor ,,of ,,chemistry ,,in ,,the ,,university ,,of ,,edinburgh4 ,,dear ,,sir1 ,i dedicate these pages to your ,children1 whom ,i often had the pleasure of seeing at the ,polytechnic during my direction of that ,institution4 ,i do so as a mark of respect and appreciation of your talent and zeal1 and of your public-spirited advocacy of the ,claims of ,science in this great and commercial country4 ,without making you responsible in any way for the shortcomings of this humble work on ,elementary ,science1 allow me to subscribe myself1 ,dear ,sir1 ,yours most respectfully1 ,,john ,,henry ,,pepper4 ,,contents4 ,,page ,,introduction #a ,,chapter ,i4 ,,the ,,properties ,,of ,,matter--,,impenetrability #c ,,chapter ,,ii4 ,,centrifugal ,,force #ag ,,chapter ,,iii4 ,,the ,,science ,,of ,,astronomy #ai ,,chapter ,,iv4 ,,centre ,,of ,,gravity #cb ,,chapter ,v4 ,,specific ,,gravity #dh ,,chapter ,,vi4 ,,attraction ,,of ,,cohesion #ei ,,chapter ,,vii4 ,,adhesive ,,attraction #fg ,,chapter ,,viii4 ,,capillary ,,attraction #fi ,,chapter ,,ix4 ,,crystallization #gc ,,chapter ,x4 ,,chemistry #ha ,,chapter ,,xi4 ,,chlorine1 ,,iodine1 ,,bromine1 ,,fluorine #abi ,,chapter ,,xii4 ,,carbon1 ,,boron1 ,,silicon1 ,,selenium1 ,,sulphur1 ,,phosphorus #aea ,,chapter ,,xiii4 ,,frictional ,,electricity #agc ,,chapter ,,xiv4 ,,voltaic ,,electricity #aic ,,chapter ,,xv4 ,,magnetism ,,and ,,electro-,,magnetism #bjf ,,chapter ,,xvi4 ,,electro-,,magnetic ,,machines #baa ,,chapter ,,xvii4 ,,the ,,electric ,,telegraph #bah ,,chapter ,,xviii4 ,,ruhmkorff',s1 ,,hearder',s1 ,,and ,,bentley',s ,,coil ,,appararatus #bcj ,,chapter ,,xix4 ,,magneto-,,electricity #bda ,,chapter ,,xx4 ,,dia-,,magnetism #bdg ,,chapter ,,xxi4 ,,light1 ,,optics1 ,,and ,,optical ,,instruments #bee ,,chapter ,,xxii4 ,,the ,,refraction ,,of ,,light #bih ,,chapter ,,xxiii4 ,,refracting ,,optical ,,instruments #cjc ,,chapter ,,xxiv4 ,,the ,,absorption ,,of ,,light #cbg ,,chapter ,,xxv4 ,,the ,,inflection ,,or ,,diffraction ,,of ,,light #cbh ,,chapter ,,xxvi4 ,,the ,,polarization ,,of ,,light #cce ,,chapter ,,xxvii4 ,,heat #ceb ,,chapter ,,xxviii4 ,,the ,,steam-,,engine #djf ,,chapter ,,xxix4 ,,the ,,steam-,,engine--continued #dah ,page #a ,,introduction4 ,although ,the ,south ,kensington ,museum now takes the lead1 and surpasses all former scientific institutions by its vastly superior collection of models and works of art1 there will be doubtless many thousand young people who may remember 7it is hoped7 with some pleasure the numerous popular lectures1 illustrated with an abundance of interesting and brilliant experiments1 which have been delivered within the walls of the ,royal ,polytechnic ,institution during the last twenty years4 ,on many occasions the author has received from his young friends letters1 containing all sorts of inquiries respecting the mode of performing experiments1 and it has frequently occurred that even some years after a lecture had been discontinued1 the youth1 now become the young man1 and anxious to impart knowledge to some home circle or country scientific institution1 would write a special letter referring to a particular experiment1 and wish to know how it was performed4 ,the following illustrated pages must be regarded as a series of philosophical experiments detailed in such a manner that any young person may perform them with the greatest facility4 ,the author has endeavoured to arrange the manipulations in a methodical1 simple1 and popular form1 and will indeed be rewarded if these experiments should arouse dormant talent in any of the rising generation1 and lead them on gradually from the easy reading of the present ,boy's ,book1 to the study of the complete and perfect philosophical works of ,leopold ,gmelin1 ,faraday1 ,brande1 ,graham1 ,turner1 and ,fownes4 ,every boy should ride a hobby-horse of some kind2 and whilst play1 and plenty of it1 must be his daily right in holiday time1 he ought not to forget that the cultivation of some branch of the useful ,arts and ,sciences will afford him a delightful and profitable recreation when ,page #bsatiated with mere play1 or imprisoned by bad weather1 or gloomy with the unamused tediousness of a long winter's evening4 ,the author recollects with pleasure the half-holidays he used to devote to ,chemistry1 with some other ,king's ,college lads1 and in spite of terrible pecuniary losses in retorts1 bottles1 and jars1 the most delightful amusement was enjoyed by all who attended and assisted at these juvenile philosophical meetings4 ,it has been well remarked by a clever author1 that bees are geometricians4 ,the cells are so constructed as1 with the least quantity of material1 to have the largest sized spaces and the least possible interstices4 ,the mole is a meteorologist4 ,the bird called the nine-killer is an arithmetician1 also the crow1 the wild turkey1 and some other birds4 ,the torpedo1 the ray1 and the electric eel are electricians4 ,the nautilus is a navigator4 ,he raises and lowers his sails1 casts and weighs anchor1 and performs nautical feats4 ,whole tribes of birds are musicians4 ,the beaver is an architect1 builder1 and wood-cutter4 ,he cuts down trees and erects houses and dams4 ,the marmot is a civil engineer4 ,he does not only build houses1 but constructs aqueducts1 and drains to keep them dry4 ,the ant maintains a regular standing army4 ,wasps are paper manufacturers4 ,caterpillars are silk-spinners4 ,the squirrel is a ferryman4 ,with a chip or a piece of bark for a boat1 and his tail for a sail1 he crosses a stream4 ,dogs1 wolves1 jackals1 and many others1 are hunters4 ,the black bear and heron are fishermen4 ,the ants are day-labourers4 ,the monkey is a rope dancer4 ,shall it1 then1 be said that any boy possessing the ,godlike attributes of ,mind and ,thought with ,freewill can only eat1 drink1 sleep1 and play1 and is therefore lower in the scale of usefulness than these poor birds1 beasts1 fishes1 and insects8 ,no6 no6 ,let ,young ,england enjoy his manly sports and pastimes1 but let him not forget the mental race he has to run with the educated of his own and of other nations2 let him nourish the desire for the acquisition of scientific knowledge1 not as a mere school lesson1 but as a treasure1 a useful ally which may some day help him in a greater or lesser degree to fight ,the ,battle of ,life4 ,page #c ,,the ,,boy',s ,,playbook ,,of ,,science4 ,,chapter ,i4 ,,the ,,properties ,,of ,,matter--,,impenetrability4 ,in the present state of our knowledge it seems to be universally agreed1 that we cannot properly commence even popular discussions on astronomy1 mechanics1 and chemistry1 or on the imponderables1 heat1 light1 electricity1 and magnetism1 without a definition of the general term matter2 which is an expression applied by philosophers to every species of substance capable of occupying space1 and1 therefore1 to everything which can be seen and felt4 ,the sun1 the moon1 the earth1 and other planets1 rocks1 earths1 metals1 glass1 wool1 oils1 water1 alcohol1 air1 steam1 and hosts of things1 both great and small1 all solids1 liquids and gases1 are included under the comprehensive term matter4 ,such a numerous and varied collection of bodies must necessarily have certain qualities1 peculiarities1 or properties2 and hence we come in the first place to consider ,the general powers or properties of matter4 ,thus1 if we place a block of wood or stone in any position1 we cannot take another substance and put it in the space filled by the wood or stone1 until the latter be removed4 ,now this is one of the first and most simple of the properties of matter1 and is called impenetrability1 being the property possessed by all solid1 liquid1 and gaseous bodies1 of filling a space to the exclusion of others until they be removed1 and it admits of many amusing illustrations1 both as regards the proof and modification of the property4 ,thus1 a block of wood fills a certain space3 how is it 7if impenetrable7 that we can drive a nail into it8 ,a few experiments will enable us to answer this question4 ,into a glass 7as depicted at fig4 #a7 filled with spirits of wine1 a quantity of cotton wool many times the bulk of the alcohol may 7if the experiment is carefully performed7 be pushed without causing a drop to overflow the sides of the vessel4 ,here we seem to have a direct contradiction of the simple and ,page #d indisputable truth1 that two things cannot occupy the same space at once4 ,but let us proceed with our experiments3-- ,we have now a flask full of water1 and taking some very finely-powdered sugar1 it is easy to introduce a notable quantity of that substance without increasing the bulk of the water2 the only precaution necessary1 is not to allow the sugar to fall into the flask in a mass1 but to drop it in grain by grain1 and very slowly1 allowing time for the air-bubbles 7which will cling to the particles of sugar7 to pass off1 and for the sugar to dissolve4 ,matter1 in the experiments adduced1 appears to be penetrable1 and the property of impenetrability seems only to be a creation of fancy3 reason1 however1 enables us to say that the latter is not the case4 ,illustration3 ,fig4 #a4 ,illustration3 ,fig4 #b4 ,a nail may certainly be hammered into wood1 but the particles are thrust aside to allow it to enter4 ,cotton wool may be placed in spirits of wine because it is simply greatly extended and bulky matter1 which1 if compressed1 might only occupy the space of the kernel of a nut1 and if this were dropped into a half-pint measure full of alcohol1 the increase of bulk would not cause the spirit to ,page #e overflow4 ,the cotton-wool experiment is therefore no contradiction of impenetrability4 ,the experiment with the sugar is the most troublesome opponent to our term1 and obliges us to amend and qualify the original definition1 and say1 that the ultimate or smallest particles or atoms of bodies only are impenetrable2 and we may believe they are not in close contact with each other1 because certain bulks of sugar and water occupy more space separately than when mixed4 ,illustration3 ,fig4 #c4 ,if we compare the flask of water to a flask full of marbles1 and the sugar to some rape-seed1 it will be evident that we may almost pour another flask full of the latter amongst the marbles1 because they are not in close contact with each other1 but have spaces between them2 and after pouring in the rape-seed1 we might still find room for some fine sand4 ,the particles of one body may thus enter into the spaces left between those of another without increasing its volume2 and hence1 as has been before stated1 ,the atoms only of bodies are truly impenetrable4 ,this spreading1 as it were1 of matter through matter assumes a very important function when we come to examine the constitution of the air we breathe1 which is chiefly a mechanical mixture of gases3 seventy-nine parts by volume or measure of nitrogen gas1 twenty-one parts of oxygen gas1 and four parts of carbonic acid vapour in every ten thousand parts of air having the following relations as to weight3-- ,specific gravity4 ,nitrogen #igb ,oxygen #aaje ,carbonic acid #aebd ,illustration3 ,fig4 #d4 ,illustration3 ,fig4 #e4 ,a4 ,the porous cell4 ,b4 ,the jar of hydrogen4 ,c4 ,the brass cap and glass tube ,d1 the end of which dips into the tumbler containing the solution of indigo ,e4 ,f ,f4 ,the wire and stand supporting the porous cell and tube in tumbler4 ,it might be expected that these gases would arrange themselves in our atmosphere in the above order1 and if that were the case1 we should have the carbonic-acid gas 7a most poisonous one7 at the bottom1 and touching the earth1 then the oxygen1 and1 last of all1 the nitrogen2 ,page #f a state of things in which organized life could not exist4 ,the gases do not1 however1 separate3 indeed1 they seem to act as it were like vacuums to one another1 and the diffusion of gases has become a recognised fact1 governed by fixed laws4 ,this fact is curiously illustrated1 as shown in our cut1 by filling a bottle with carbonic acid1 and another with hydrogen2 and having previously fitted corks to the bottles1 perforated so as to admit a tube1 place the bottle containing the carbonic acid on the table1 then take the other full of hydrogen1 keeping the mouth downwards1 and fit in the cork and tube3 place this finally into the cork of the carbonic-acid bottle1 which may be a little larger than the other1 in order to make the arrangement stand firmer2 and after leaving them for an hour or so1 the carbonic acid1 which is twenty-two times heavier than the hydrogen1 will ascend to the latter1 whilst the hydrogen will descend to the carbonic acid4 ,the presence of the carbonic acid in the hydrogen bottle is easily proved by pouring in a wine-glassful of clear lime-water1 which speedily becomes milky1 owing to the production of carbonate of lime2 whilst the proof of the hydrogen being present in the carbonic acid is established by absorbing the latter with a little cream of lime--i4e41 slacked lime mixed to the consistence of cream with some water--and setting fire to the hydrogen that remains1 which burns quietly with a yellowish flame if unmixed with air2 but if air be admitted to the bottle1 the mixture of air and hydrogen inflames rapidly1 and with some noise4 ,one of the most elegant modes of showing the diffusion of gases is by taking a large round dry porous cell1 such as would be employed in a voltaic battery1 and having cemented a brass cap with a glass tube attached to its open extremity1 it may then be supported by a small tripod of iron ,page #g wire1 and the end of the glass tube placed in a tumbler containing a small quantity of water coloured blue with sulphate of indigo4 ,if a tolerably large jar containing hydrogen is now placed over the porous cell1 bubbles of gas make their escape at the end of the tube1 because the hydrogen diffuses itself more rapidly into the porous cell than the air which it already contains passes out4 ,when the jar is removed1 the reverse occurs1 hydrogen diffuses out of the porous cell1 and the blue liquid rises in the tube4 ,this diffusive force prevents the accumulation of the various noxious gases on the earth1 and spreads them rapidly through the great bulk of the atmosphere surrounding the globe4 ,although air and other gases are invisible1 they possess the property of impenetrability1 as may be easily proved by various experiments4 ,having opened a pair of common bellows1 stop up the nozzle securely1 and it is then impossible to shut them2 or1 fill a bladder with air by blowing into it1 and tie a string fast round the neck2 you then find that you cannot1 without breaking the bladder1 press the sides together4 ,illustration3 ,fig4 #f4 represents the water overflowing1 as the glass1 with the orifice closed1 is pressed down1 proving the impenetrability of air4 ,illustration3 ,fig4 #g4 ,the orange has entered the glass vessel1 and the air having passed from the orifice1 no water overflows4 ,it is customary to say that a vessel is empty when we have poured out the water which it contained4 ,having provided two glass vessels full of water1 place each of them in an empty white pan1 to receive the overflow1 then lay an orange upon the surface of the water of one of them1 and being provided with a cylindrical glass1 open at one end1 with a hole in the centre of the closed end1 place your finger firmly over the orifice1 and endeavour1 by inverting the glass over the orange1 and pressing upon the surface of the water1 to make it enter the interior of the glass cylinder2 the resistance of the air will now cause the water to overflow into the white pan1 whilst the orange will not enter4 ,the ,page #h orange may now be transferred to the other vessel of water1 and on removing the finger from the orifice of the cylindrical glass1 and inverting it as before over the orange1 the air will rush out and the orange and water will enter1 whilst there will be no overflow as in the preceding experiment4 ,the comparison of the two is very striking1 and at once teaches the fact desired4 ,illustration3 ,fig4 #h4 ,gas-jar with stop-cock closed1 and potassium in ladle2 air prevents the entrance of the water4 ,illustration3 ,fig4 #i4 ,gas-jar2 stop-cock open2 the air passes1 the water enters1 and the potassium is inflamed4 ,whilst the vessels of water are still in use1 another pretty experiment may be made with the metal potassium4 ,first throw a small piece of the metal on the surface of the water1 to show that it takes fire on contact with that fluid2 then1 having provided a gas-jar1 fitted with a cap and stop-cock1 and a little spoon screwed into the bottom of the stop-cock inside the gas-jar1 place another piece of potassium in the little spoon1 and1 after closing the stop-cock1 push the jar into one of the vessels of water3 as before1 the impenetrability of the air prevents the water flowing up to the potassium2 but1 on opening the stop-cock1 the air escapes1 the water rushes up1 and directly it touches the potassium1 combustion ensues4 ,having sufficiently indicated the nature and meaning of impenetrability1 we may proceed to discuss experimentally three other marked and special qualities of matter--viz41 inertia1 gravity1 and weight4 ,page #i ,,inertia1 ,,or ,,passiveness4 ,inertia is a power which 7according to ,sir ,isaac ,newton7 is implanted in all matter of resisting any change from a state of rest4 ,it is sometimes called vis inerti1 and is that property possessed by all matter1 of remaining at rest till set in motion1 and vice vers2 and it expresses1 in brief terms1 resistance to motion or rest4 ,illustration3 ,fig4 #aj4 ,tin tray1 with glass bottom1 full of water2 candle placed underneath4 ,a pendulum clock wound up and ready to go1 does not commence its movements1 until the inertia of the pendulum is overcome1 and motion imparted to it4 ,on the other hand1 when seated in a carriage1 should any obstruction cause the horse to stop suddenly1 it is only perhaps by a violent effort1 if at all1 that we can resist the onward movement of our bodies4 ,to illustrate inertia1 construct a metal tray1 about three feet long1 two feet wide1 and two inches deep1 with a glass bottom1 and arrange it on a framework supported by legs1 like a table1 and having filled it with water1 let the room be darkened1 and then place under the tank a lighted candle1 at a sufficient distance from the glass to prevent the heat cracking it4 ,if a piece of calico or paper1 stretched on a framework1 be now held over the water at an angle of about thirty degrees1 all that occurs on the surface of the water will be rendered visible on such screen4 ,attention may now be directed to the quiescence1 or the inertia of the water1 while the opposite condition of movement and formation of the waves may be beautifully shown by touching the surface of the water with the finger2 the miniature waves being depicted on the screen1 and continuing their motion till set at rest by striking against the sides of the tin tray4 ,illustration3 ,fig4 #aa4 ,same tray1 with calico screen2 showing the waves as they are produced by touching the surface of the water with the finger4 ,page #aj ,should the above experiment be thought too troublesome or expensive to prepare1 inertia may be demonstrated by filling a tea-cup or other convenient vessel with water1 and after moving rapidly with it in any direction1 if we stop suddenly1 the rigidity of all parts of the cup we hold brings them simultaneously to a state of rest2 but the mobility of the liquid particles allows of their continuing in motion in their original direction1 and the liquid is spilled4 ,thus1 carelessness in handing and spilling a cup of tea 7though not to be recommended7 serves to illustrate an important principle4 ,the inertia of bodies in motion is further and lamentably illustrated by the accidents caused from the sudden stoppage of a railway train whilst in rapid motion1 when heads and knees come in contact with frightful results4--,it is more especially demonstrated by the earth1 the moon1 and the other planets continuing their motion for ever in the absence of any friction or resistance to oppose their onward progress4 ,it is the friction arising from the roughness of the ground1 the resistance of the air1 and the force of the earth's attraction1 which puts a stop to bodies set in motion about the surface of the earth4 ,page #aa ,,gravitation4 ,inertia represents a passive force1 gravitation1 an active condition of matter2 and this latter may truly be termed a force of attraction1 because it acts between masses at sensible or insensible distances3 it is illustrated by a stone1 unsupported1 falling to the ground2 by the stone pressing with force on the earth1 and requiring power to raise it from the ground3 indeed1 it is commonly reported that it was by an accident--an apple falling from a tree--that the great ,newton was led to reflect on the universal law of gravitation1 and to pronounce upon it in the following memorable words3-- ,every particle of matter in the universe attracts every other particle of matter with a force or power directly proportional to the quantity of matter in each1 and decreasing as the squares of the distances which separate the particles increase4 ,these words may appear very obscure to our juvenile readers2 but when dissected and examined properly1 they clearly define the property of gravitation4 ,for instance1 every particle attracts every other with a force proportional to the quantity of matter in each4 ,this statement was verified some years back by ,maskelyne1 who1 having sought out and discovered a steep1 precipitous rock in the ,schichallion mountains1 in ,scotland1 suspended from it a metal weight by a cord1 and going to a convenient distance with a telescope1 and observing the weight1 he found that it did not hang perpendicularly1 like an ordinary plumb line1 but was attracted1 or impelled1 to the sides of the rock by some kind of attraction1 which1 of course1 could be no other than that indicated by ,newton as the attraction of gravitation4 ,illustration3 ,fig4 #ab4 ,the ,schichallion ,rocks4 ,the dotted line and weight ,a represent the ordinary position of a plumb line1 whilst the line of the weight ,b indicates 7of course1 with some exaggeration7 the attractive power of the mass of the rock drawing it from the perpendicular4 ,this truly wonderful power of attraction pervades all masses2 and being1 as before stated1 proportional to the quantity of matter1 if a man could be transported to the surface of the sun1 he would become about thirty times heavier3 he would be attracted1 or impelled1 to the sun with thirty times more gravitating force than on the surface of the earth1 and would weigh about two tons4 ,of course1 nursing a baby on the sun's surface would be a very serious affair with our ordinary strength2 whilst on some of the smaller planets1 such as ,ceres and ,pallas1 we should probably gravitate with a force of a few pounds only1 and with the same muscular power now possessed1 we should quite emulate the exploits of those domestic little creatures sometimes called the industrious fleas1 and our jumping would be something marvellous4 ,page #ab ,there is no very good lecture-table experiment that will illustrate gravitation1 although attention may be directed to the fact of a piece of potassium thrown on the surface of water in a plate generally rushing to the sides1 and1 as if attracted1 attaching itself with great force to the substance of the pottery or porcelain2 or1 if a model ship1 or lump of wood1 be allowed to float at rest in a large tank of water1 and a number of light chips of wood or bits of straw be thrown in1 they generally collect and remain around the larger floating mass4 ,illustration3 ,fig4 #ac4 ,a4 ,the centre ball1 representing the earth's centre of gravity4 ,w ,w ,w ,w4 ,four wires fixed into centre ball1 and passing through and secured in the hoop1 projecting about one foot from the circumference4 ,b ,b ,b ,b4 ,two balls--a model ship and toy--working on the wires like beads1 with vulcanized ,india-rubber straps attached to them and the circumference of the hoop4 ,a very good idea1 however1 may be afforded of the universal action of gravity maintaining all things in their natural position on the earth by ,page #ac taking a hoop and arranging in and upon it balls1 or a model ship1 or other toy1 and wires1 as depicted in our diagram4 ,with this simple apparatus we may illustrate the upward1 downward1 and sideway movement of bodies from the earth1 and the counteraction by the force of gravitation of any tendency of matter to fall away from the globe1 which is represented in the model by the india-rubber springs pulling the balls and toys back again to the circumference of the hoop4 ,the attraction of gravitation decreases 7quoting the remainder of ,newton's definition7 as the squares of the distances which separate the particles increase--i4e41 it obeys the principle called inverse proportion--viz41 the greater the distance1 the less gravitating power2 the less the distance1 the greater the power of gravitation4 ,gravitation is like the distribution of light and other radiant forces1 and may be thus illustrated4 ,illustration3 ,fig4 #ad4 ,place a lighted candle1 marked ,a1 at a certain distance from ,no4 #a1 a board one foot square2 at double the distance the latter will shadow another board1 ,no4 #b1 four feet square2 at three times1 ,no4 #c1 nine feet square2 at four1 ,no4 #d1 sixteen feet2 and so on4 ,to make the comparison between the propagation of light and the attraction of gravitation1 we have only to imagine the candle1 a1 to represent the point where the force of gravity exists in the highest degree of intensity2 suppose it to be the sun--the great centre of this power in our planetary system4 ,a body1 as at ,no4 #a1 at any given distance will be attracted 7like iron-filings to a magnet7 with a certain force2 at twice the distance1 the square of two being four1 and by inverse proportion1 the attraction will be four times less2 at thrice the distance1 nine times less2 at the fourth distance1 sixteen times less2 and so on4 ,with the assistance of this law1 we may calculate1 roughly1 the depth of a well1 or a precipice1 or a column1 by ascertaining the time occupied in the fall of a stone or other heavy substance4 ,a falling body descends about #af feet in one second1 #fd feet in two seconds1 #add feet in three seconds1 #bef feet in four seconds1 #djj feet in five seconds1 #egf feet in six seconds2 the spaces passed over being as the squares of the times4 ,suppose a stone takes three seconds in falling to the surface of the water in a well1 then #c #c #i #af #add feet would be a rough estimate of the depth4 ,the calculation will exceed the truth in consequence of the stone being retarded in its passage by the resistance of the air4 ,page #ad ,all bodies gravitate equally to the earth3 for instance1 if an open box1 say one foot in length1 two inches broad1 and two inches deep1 be provided with a nicely-fitted bottom1 attached by a hinge1 a number of substances1 such as wood1 cork1 marble1 iron1 lead1 copper1 may be arranged in a row2 and directly the hand is withdrawn1 the moveable flap flies open1 and if the manipulation with the disengagement of the trap-door is good1 the whole of the substances are seen to proceed to the earth in a straight line1 as shown in our drawing4 ,illustration3 ,fig4 #ae4 ,illustration3 ,fig4 #af4 ,if a heavy substance1 like gold1 be greatly extended by hammering and beating into thin leaves1 and then dropped from the hand1 the resistance of the air becomes very apparent2 and a gold coin and a piece of gold-leaf would not reach the earth at the same time if allowed to fall from any given height4 ,this fact is easily displayed by the assistance of a long glass cylindrical vessel placed on the air-pump1 with suitable apparatus arranged with little stages to carry the different substances2 upon two of them may be placed a feather and a gold coin1 and on the third1 another gold coin and a piece of gold-leaf4 ,in arranging the experiment1 great care ought to be taken that the little stages are all nicely cleaned1 and free from any oil1 grease1 or other matter which might cause the feathers or the gold-leaf to cling to the stages when they are disengaged1 by moving the brass stop round that works in the collar of leathers4 ,sometimes these leathers are oiled1 ,page #ae and in that case1 when the vacuum is made1 the oil1 by the pressure1 is squeezed out1 and1 passing down1 may reach the stages and spoil the experiment1 by causing the feathers and gold-leaf to stick to the brass1 producing great disappointment1 as the illustration1 usually called the guinea and feather glass experiment takes some time to prepare4 ,the air-pump being in good order1 the long glass is first greased on the lower welt or edge1 and then placed firmly on the air-pump plate4 ,the top edge1 or welt1 may now be greased1 and the gold coins1 feathers1 and gold-leaf arranged in the drop-apparatus2 this is carefully placed on the top of the glass1 and firmly squeezed down4 ,the author has always found a tallow candle1 rolled in a sheet of paper 7so as to leave about half the candle exposed71 the best grease to smear the glass with for air-pump experiments2 if the weather is cold1 the candle may be placed for a few minutes before an ordinary fire to soften the tallow4 ,pomatum answers perfectly well when the surfaces of glass and brass are all nicely ground2 but as air-pumps and glasses by use get scratched and rubbed1 the tallow seems to fill up better all ordinary channels by which air may enter to spoil a vacuum4 ,illustration3 ,fig4 #ag4 ,illustration3 ,fig4 #ah4 ,the apparatus being now arranged1 the air is pumped out2 and here1 again1 care must be taken not to shake the gold off the stages4 ,when a proper vacuum has been obtained1 which will be shown by the pump-gauge1 the stop is withdrawn from one of the stages1 and the gold and feather are seen to fall simultaneously to the air-pump plate4 ,another stage1 with the gold-leaf and coin1 may now be detached2 both showing distinctly1 that when the resistance of the air is withdrawn1 all bodies1 whether called light or heavy1 gravitate equally to the earth4 ,then1 the screw at the bottom of the pump barrels ,page #af being opened1 attention may be directed to the whizzing noise the air makes on entering the vacuum1 and when the air is once more restored to the long glass vessel1 the last stage may be allowed to fall2 and now1 the gold coin reaches the pump-plate first1 and the feather1 lingering behind1 loses 7as it were7 the race1 and touches the plate after the gold coin2 thus demonstrating clearly the resistance of the air to falling bodies4 ,another1 and perhaps less troublesome1 mode of showing the same fact1 is to use a long glass tube closed at each end with brass caps cemented on4 ,one cap should have the largest possible aperture closed by a brass screw1 and the other may fit a small hand-pump4 ,if a piece of gold and a small feather are placed in the tube1 it may be shown that the former reaches the bottom of the tube first1 whilst it is full of air1 and when the air is withdrawn by means of the pump1 and the tube again inverted1 both the gold and the feather fall in the same time4 ,illustration3 ,fig4 #ai4 ,a ,b4 ,glass tube containing a piece of gold and a feather1 which are placed in at the large aperture ,a4 ,c4 ,small hand-pump4 ,for this reason1 all attempts to measure heights or depths by observing the time occupied by a falling body in reaching the earth must be incorrect1 and can only be rough approximations4 ,an experiment tried at ,st4 ,paul's ,cathedral1 with a stone1 which was allowed to fall from the cupola1 indicated the time occupied in the descent to be four and a half seconds3 now1 if we square this time1 and multiply by #af1 a height of #cbd feet is denoted2 whereas the actual height is only #bgb feet1 and the difference of #eb feet shows how the stone was retarded in its passage through the air2 for1 had there been no obstacle1 it would have reached the ground in #d-c_/bjths seconds4 ,illustration3 ,fig4 #bj4 ,the force of gravitation is further demonstrated by the action of the sun and moon raising the waters of the ocean1 and producing the tides2 and also by the earth and moon1 and other planets and satellites1 being prevented from flying from their natural paths or orbits around the sun4 ,it is also very clearly proved that there must be some kind of attractive force resident in the earth1 or else all moveable things1 the water1 the air1 the living and dead matters1 would fly away from the surface of the earth in obedience to what is called centrifugal force4 ,our earth is twenty-four hours in performing one rotation on its axis1 which is an imaginary line drawn from pole to pole1 and represented by the wire round which we cause a sphere to rotate4 ,all objects1 therefore1 on the earth are moving with the planet at an enormous velocity2 and this movement is called the earth's diurnal1 or daily rotation4 ,now1 ,page #ag it will be remembered1 that mud or other fluid matter flies off1 and is not retained by the circumference of a wheel in motion3 when a mop is trundled1 or a dog or sheep1 after exposure to rain1 shake themselves1 the water is thrown off by what is called centrifugal force 7centrum1 a centre1 fugio1 to fly from74 ,,chapter ,,ii4 ,,centrifugal ,,force4 ,that power which drives a revolving body from a centre1 and it may be illustrated by turning a closed parasol1 or umbrella1 rapidly round on its centre1 the stick being the axis--the ribs fly out1 and if there is much friction in the parts1 the illustration is more certain by attaching a bullet to the end of each rib1 as shown in our drawing4 ,illustration3 ,fig4 #ba4 ,illustration3 ,fig4 #bb4 ,the same fact may be illustrated by a square mahogany rod1 say one inch square and three feet long1 with two flaps eighteen inches in length1 hanging by hinges1 and parallel to the sides of the centre rod1 which immediately fly out on the rotation of the long centre piece4 ,the toy called the centrifugal railway is also a very pretty illustration of the same fact4 ,a glass of water1 or a coin1 may be placed in the little carriage1 and although it must be twice hanging perpendicular in a line with the earth1 the carriage does not tumble away from its appointed track1 and the centrifugal force binds it firmly to the interior of the circle round which it revolves4 ,page #ah ,illustration3 ,fig4 #bc4 ,another striking and very simple illustration is to suspend a hemispherical cup by three cords1 and having twisted them1 by turning round the cup1 it may be filled with water1 and directly the hand is withdrawn1 the torsion of the cord causes the cup to rotate1 and the water describes a circle on the floor1 flying off at a tangent from the cup1 as may be noticed in the accompanying cut4 ,illustration3 ,fig4 #bd4 ,a hoop when trundled would tumble on its side if the force of gravitation was not overcome by the centrifugal force which imparts to it a motion in the direction of a tangent 7tango1 to touch7 to a circle4 ,the same principle applies to the spinning-top--this toy cannot be made to stand upon its point until set in rapid motion4 ,returning again to the subject of gravitation1 we may now consider it in relation to other and more magnificent examples which we discover by studying the science of astronomy4 ,page #ai ,,chapter ,,iii4 ,,the ,,science ,,of ,,astronomy4 ,in a work of this kind1 professedly devoted to a very brief and popular view of the different scientific subjects1 much cannot be said on any special branch of science2 it will be better1 therefore1 to take up one subject in astronomy1 and by discussing it in a simple manner1 our young friends may be stimulated to learn more of those glorious truths which are to be found in the published works of many eminent astronomers1 and especially in that of ,mr4 ,hind1 called ,the ,illustrated ,london ,astronomy4 ,one of the most interesting subjects is the phenomenon of the eclipse of the sun2 and as #aheh is likely to be long remembered for its annular eclipse1 we shall devote some pages and illustrations to this subject4 ,eclipses of the sun are of three kinds--partial1 annular1 and total4 ,many persons have probably seen large partial eclipses of the sun1 and may possibly suppose that a total eclipse is merely an intensified form of a partial one2 but astronomers assert that no degree of partial eclipse1 even when the very smallest portion of the sun remains visible1 gives the slightest idea of a total one1 either in the solemnity and overpowering influence of the spectacle1 or the curious appearances which accompany it4 ,the late ,mr4 ,baily said of an eclipse 7usually called that of ,thales71 which caused the suspension of a battle between the ,lydians and ,medes1 that only a total eclipse could have produced the effect ascribed to it4 ,even educated astronomers1 when viewing with the naked eye the sun nearly obscured by the moon in an annular eclipse1 could not tell that any part of the sun was hidden1 and this was remarkably verified in the annular eclipse of the #aeth ,march of this year4 ,during the continuance of a total eclipse of the sun1 we are permitted a hasty glance at some of those secrets of ,nature which are not revealed at any other time--glories that hold in tremulous amazement even veteran explorers of the heavens and its starry worlds4 ,the general meaning of an eclipse may be shown very nicely by lighting a common oil1 or oxy-hydrogen lantern in a darkened room1 and throwing the rays which proceed from it on a three-feet globe4 ,the lantern may be called the sun1 and1 of course1 it is understood that correct comparative sizes are not attempted in this arrangement2 if it were so1 the globe representing the earth would have to be a mere speck1 for if we make the model of the sun in proportion to a three-feet globe1 no ordinary lecture hall would contain it4 ,this being premised1 attention is directed to the lantern1 which1 like the sun1 is self-luminous1 and is giving out its own rays2 these fall upon the globe we have designated the earth1 and illuminate one-half1 whilst the other is shrouded in darkness1 reminding us of the opacity of the earth1 and teaching1 in a familiar ,page #bj manner1 the causes of day and night4 ,another globe1 say six inches in diameter1 and supported by a string1 may be compared to the moon1 and1 like the earth1 is now luminous1 and shines only by borrowed light3 the moon is simply a reflector of light2 like a sheet of white cardboard1 or a metallic mirror4 ,when1 therefore1 the small globe is passed between the lantern and the large globe1 a shadow is cast on the large globe3 it is also seen that only the half of the small globe turned towards the lantern is illuminated1 while the other half1 opposite the large globe1 is in shadow or darkness4 ,and here we understand why the moon appears to be black while passing before the sun2 so also by moving the small globe about in various curves1 it is shown why eclipses are only visible at certain parts of the earth's surface2 and as it would take 7roughly speaking7 fifty globes as large as the moon to make one equal in size to our earth1 the shadow it casts must necessarily be small1 and cannot obscure the whole hemisphere of the earth turned towards it4 ,an eclipse of the sun is1 therefore1 caused by the opaque mass of moon passing between the sun and the earth4 ,whilst an eclipse of the moon is caused by the earth moving directly between the sun and the moon3 the large shadow cast by the earth renders a total eclipse of the moon visible to a greater number of spectators on that half of the earth turned towards the moon4 ,all these facts can be clearly demonstrated with the arrangement already described1 of which we give the following pictorial illustration3-- ,illustration3 ,fig4 #be4 ,in using this apparatus1 it should be explained that if the moon were as large as the sun1 the shadow would be cylindrical like the figure #a1 and of an unlimited length4 ,if she were of greater magnitude1 it would precisely resemble the shadow cast in the experiment already adduced with the lantern and shown at ,no4 #b4 ,but being so very much smaller than the sun1 the moon projects a shadow which converges to a point as shown in the third diagram4 ,page #ba ,illustration3 ,fig4 #bf4 ,illustration3 ,fig4 #bg4 ,illustration3 ,fig4 #bh4 ,in order to comprehend the difference between an annular and a total eclipse of the sun1 it is necessary to mention the apparent sizes of the sun and moon3 thus1 the former is a very large body--viz41 eight hundred and eighty-seven thousand miles in diameter2 but then1 the sun is a very long way off from the earth1 and is ninety millions of miles distant from us2 therefore1 he does not appear to be very large3 indeed1 the sun seems to be about the same size as the moon2 for1 although the sun's diameter is 7roughly speaking7 four hundred times greater than that of the moon1 he is four hundred times further away from us1 and1 consequently1 the sun and moon appear to be the same size1 and when they come in a straight line with the eye1 the nearer and smaller body1 the moon1 covers the larger and more distant mass1 the sun2 and hence1 we have either an annular1 or a total eclipse1 showing how a small body may come between the eye and a larger body1 and either partially or completely obscure it4 ,page #bb ,with respect to an annular eclipse1 it must be remembered1 that the paths of all bodies revolving round others are elliptical2 i4e41 they take place in the form of an ellipse1 which is a figure easily demonstrated2 and is1 in fact1 one of the conic sections4 ,if a slice be taken off a cone1 parallel with the base1 we have a circle thus-- ,illustration3 ,fig4 #bi4 ,if it be cut obliquely1 or slanting1 we see at once the figure spoken of1 and have the ellipse as shown in this picture4 ,illustration3 ,fig4 #cj4 ,now1 the ellipse has two points within it1 called the foci1 and these are easily indicated by drawing an ellipse on a diagram-board1 in which two nails have been placed in a straight line1 and about twelve inches apart4 ,having tied a string so as to make a loop1 or endless cord1 a circle may first be drawn by putting the cord round one of the nails1 and holding a piece of chalk in the loop of the string1 it may be extended to its full distance1 and a circle described2 here a figure is produced round one point1 and to show the difference between a circle and an ellipse1 the endless cord is now placed on the two nails1 and the chalk being carried round inside the string1 no longer produces the circle1 but that familiar form called the oval4 ,as a gardener would say1 an oval has been struck2 and the two points round which it has been described1 ,page #bc are called the foci4 ,this explanation enables us to understand the next diagram1 showing the motion of the earth round the sun2 the latter being placed in one of the foci of a very moderate ellipse1 and the various points of the earth's orbit designated by the little round globes marked ,a1 ,b1 ,c1 ,d1 where it is evident that the earth is nearer to the sun at ,b than at ,d4 ,in this diagram the ellipse is exaggerated1 as it ought1 in fact1 to be very nearly a circle4 ,illustration3 ,fig4 #ca4 ,illustration3 ,fig4 #cb4 ,we are about three millions of miles nearer to the sun in the winter than we are in the summer2 but from the more oblique or slanting direction of the rays of the sun during the winter season1 we do not derive any increased heat from the greater proximity4 ,the sun1 therefore1 apparently varies in size2 but this seeming difference is so trifling that it is of no importance in the discussion3 and here we may ask1 why does ,page #bd the earth move round the sun8 ,because it is impelled by two forces1 one of which has already been fully explained1 and is called the centrifugal power1 and the other1 although termed the centripetal force1 is only another name for the attraction of gravitation4 ,illustration3 ,fig4 #cc4 ,illustration3 ,fig4 #cd4 ,to show their mutual relations1 let us suppose that1 at the creation of the universe1 the earth1 marked ,a1 was hurled from the hand of its ,maker2 according to the law of inertia1 it would continue in a straight line1 ,a ,c1 for ever through space1 provided it met with no resistance or obstruction4 ,let us now suppose the earth to have arrived at the point ,b1 and to come within the sphere of the attraction of the sun ,s2 ,page #be here we have at once contending forces acting at right angles to each other2 either the earth must continue in its original direction1 ,a ,c1 or fall gradually to the sun4 ,but1 mark the beauty and harmony of the arrangement3 like a billiard-ball1 struck with equal force at two points at right angles to each other1 it takes the mean between the two1 or what is termed the diagonal of the parallelogram 7as shown in our drawing of a billiard-table71 and passes in the direction of the curved line1 ,b ,d2 having reached ,d1 it is again ready to fly off at a tangent2 the centrifugal force would carry it to ,e1 but again the gravitating force controls the centripetal1 and the earth pursues its elliptical path1 or orbit1 till the ,almighty ,author who bade it move shall please to reverse the command4 ,illustration3 ,fig4 #ce4 ,the mutual relations of the centripetal and centrifugal forces may be illustrated by suspending a tin cylindrical vessel by two strings1 and having filled it with water1 the vessel may be swung round without spilling a single drop2 of course1 the movement must be commenced carefully1 by making it oscillate like a pendulum4 ,illustration3 ,fig4 #cf4 ,the cord which binds it to the finger may be compared to the centripetal force1 whilst the centrifugal power is illustrated by the water pressing against the sides and remaining in the vessel4 ,upon the like principles the moon revolves about the earth1 but her orbit is more elliptical than that of the earth around the sun2 and it is evident from our diagram that the moon is much further from the earth at ,a than at ,b4 ,as a natural consequence1 the moon appears sometimes a little larger and sometimes smaller than the sun2 the apparent mean diameter of the latter being thirty-two minutes1 whilst the moon's apparent diameter varies from twenty-nine and a half to thirty-three and a half minutes4 ,now1 if the moon passes exactly between us and the sun when she is apparently largest1 then a total eclipse takes place2 whereas1 if she glides between the sun and ourselves when smallest--i4e41 when furthest off from the earth--then she is not sufficiently ,page #bf large to cover the sun entirely1 but a ring of sunlight remains visible around her1 and what is called an annular eclipse of the sun occurs4 ,this fact may be shown in an effective manner by placing the oxy-hydrogen lantern before a sheet1 or other white surface1 and throwing a bright circle of light upon it1 which may be called the sun2 then1 if a round disc of wood be passed between the lantern and the sheet1 at a certain distance from the nozzle of the lantern1 all the light is cut off1 the circle of light is no longer apparent1 and we have a resemblance to a total eclipse4 ,illustration3 ,fig4 #cg4 ,by taking the round disc of wood further from the lantern1 and repeating the experiment1 it will be found that the whole circle of light is not obscured1 but a ring of light appears around the dark centre1 corresponding with the phenomenon called the annular 7ring-shaped7 eclipse4 ,if a bullet be placed very near to one eye whilst the other remains closed1 a large target may be wholly shut out from vision2 but if the bullet be adjusted at a greater distance from the eye1 then the centre only will be obscured1 and the outer edge or ring of the target remains visible4 ,when the advancing edge1 or first limb1 as it is termed1 of the moon approaches very near to the second limb of the sun1 the two are joined together for a time by alternations of black and white points1 called ,baily's beads4 ,this phenomenon is supposed to be caused partly by the uneven and mountainous edge of the moon1 and partly by that inevitable fault of telescopes1 and of the nervous system of the eye1 which tends to enlarge the images of luminous objects1 producing what is called irradiation4 ,it is exceedingly interesting to know that1 although the clouds obscured the annular eclipse of #aheh1 in many parts of ,england1 we are yet ,page #bg left the recorded observations of one fortunate astronomer1 ,mr4 ,john ,yeats1 who states that-- ,all the phenomena of an annular eclipse were clearly and beautifully visible on the ,fotheringay-,castle-mound1 which is a locality easily identified4 ,baily's beads were perfectly plain on the completion of the annulus1 which occurrence took place1 according to my observation1 at about seventy seconds after #a o'clock2 it lasted about eighty seconds4 ,the 'beads1' like drops of water1 appeared on the upper and under sides of the moon1 occupying fully three-fourths of her circumference4 ,prior to this1 the upper edge of the moon seemed dark and rough1 and there were no other changes of colour4 ,at #ab4dc1 the cusps1 for a few moments1 bore a very black aspect4 ,there was nothing like intense darkness during the eclipse1 and less gloom than during a thunderstorm4 ,bystanders prognosticated rain2 but it was the shadow of a rapidly-declining day4 ,at #ab o'clock1 a lady living on the farm suddenly exclaimed1 ',the cows are coming home to be milked6' and they came1 all but one2 that followed1 however1 within the hour4 ,cocks crowed1 birds flew low or fluttered about uneasily1 but every object far and near was well defined to the eye4 ,a singular broadway of light stretched north and south for upwards of a quarter of an hour2 from about #ab4ed to #a4aj ,p4,m4 ,illustration3 ,fig4 #ch4 ,illustration3 ,fig4 #ci4 ,if the annular eclipse of the sun be a matter for wonderment1 the total eclipse of the same is much more surprising2 no other expression than that of awfully grand1 can give an idea of the effects of totality1 and of the suddenness with which it obscures the light of heaven4 ,the darkness1 it is said1 comes dropping down like a mantle1 and as the moment of full obscuration approaches1 people's countenances become livid1 the horizon is indistinct and sometimes invisible1 and there is a general appearance of horror on all sides4 ,these are not simply the inventions ,page #bh of active human imaginations1 for they produce equal1 if not greater effects1 upon the brute creation4 ,m4 ,arago quotes an instance of a half-starved dog1 who was voraciously devouring some food1 but dropped it the instant the darkness came on4 ,a swarm of ants1 busily engaged1 stopped when the darkness commenced1 and remained motionless till the light reappeared4 ,a herd of oxen collected themselves into a circle and stood still1 with their horns outward1 as if to resist a common enemy2 certain plants1 such as the convolvulus and silk-tree acacia1 closed their leaves4 ,the latter statement was corroborated during the annular eclipse of the #aeth of ,march1 #aheh1 by ,mr4 ,e4 ,s4 ,lane1 who states1 that crocuses at the ,observatory1 ,beeston1 had their blossoms expanded before the eclipse2 they commenced closing1 and were quite shut at about one minute previous to the greatest darkness2 and the flowers opened partially about twenty minutes afterwards4 ,a total eclipse of the sun has always impressed the human mind with terror and wonder in every age3 it was always supposed to be the forerunner of evil2 and not only is the mind powerfully impressed1 as darkness gradually shuts out the face of the sun1 but at the moment of totality1 a magnificent corona1 or glory of light1 is visible1 and prominences1 or flames1 as they are often termed1 make their appearance at different points round the circle of the dark mass4 ,this glory does not flash suddenly on the eye2 but commencing at the first limb of the sun1 passes quickly from one limb to the other4 ,our illustration shows the corona and the rose-coloured prominences1 whose nature we shall next endeavour to explain4 ,professor ,airy describes the change from the last narrow crescent of light to the entire dark moon1 surrounded by a ring of faint light1 as most curious1 striking1 and magical in effect4 ,the progress of the formation of the corona was seen distinctly4 ,page #bi ,it commenced on the side of the moon opposite to that at which the sun disappeared1 and in the general decay and disease which seemed to oppress all nature1 the moon and the corona appeared almost like a local sore in that part of the sky1 and in some places were seen double4 ,its texture appeared as if fibrous1 or composed of entangled threads2 in other places brushes1 or feathers of light proceeded from it1 and one estimate calculated the light at about one-seventh part of a full moon light4 ,the question1 whether the corona is concentric with the sun and moon1 was specially mooted by ,m4 ,arago1 and ,professor ,baden ,powell has produced such excellent imitations of the corona by making opaque bodies occult1 or conceal1 very bright points1 that it cannot be considered as material or real1 although it ought to be remembered that the best theory of the zodiacal light represents it to be a nebulous mass1 increasing in density towards the sun1 and yet no portion of this nebulous mass was seen during the totality4 ,but by far the most remarkable of all the appearances connected with a total eclipse are the rose-coloured prominences1 mountains1 or flames1 projecting from the circumference of the moon to the inner ring of the corona2 and1 although they had been observed by ,vaserius 7a ,swedish astronomer7 in #agcc1 they took the modern astronomers entirely by surprise in #ahdb1 and they were not prepared with instruments to ascertain the nature of these strange and almost portentous forms4 ,in #ahea1 however1 great preparations were made to throw further light on the subject4 ,professor ,airy went to make his observations1 and he says1 ,that the suddenness of the darkness in #ahea appeared much more striking than in #ahdb1 and the forms of the rose-coloured mountains were most curious4 ,one reminded him of a boomerang 7that curious weapon thrown so skilfully by the aborigines of ,australia72 this same figure has been spoken of by others as resembling a ,turkish scimitar1 strongly coloured with rose-red at the borders1 but paler in the centre4 ,another form was a pale-white semicircle based on the moon's limbs2 a third figure was a red detached cloud1 or balloon1 of nearly circular form1 separated from the moon by nearly its own breadth2 a fourth appeared like a small triangle1 or conical red mountain1 perhaps a little white in the interior2 and the ,professor proceeds to say1 ,i employed myself in an attempt to draw roughly the figures1 and it was impossible1 after witnessing the increase in height of some1 and the disappearance of another1 and the arrival of new forms1 not to feel convinced that the phenomena belonged to the sun1 and not to the moon4 ,still the question remains unanswered1 what are these rose-coloured prominences8 ,if they belong to the sun1 and are mountains in that luminary1 they must be some thirty or forty thousand miles in height4 ,m4 ,faye has formally propounded the theory1 that they are caused by refraction1 or a kind of mirage1 or the distortion of objects caused by heated air4 ,this phenomenon is not peculiar to any country1 though most frequently observed near the margin of lakes and rivers1 and on hot sandy plains4 ,m4 ,monge1 who accompanied ,buonaparte in his ,page #cj expedition to ,egypt1 witnessed a remarkable example between ,alexandria and ,cairo1 where1 in all directions1 green islands appeared surrounded by extensive lakes of pure1 transparent water4 ,m4 ,monge states that ,nothing could be conceived more lovely or picturesque than the landscape4 ,in the tranquil surface of the lake1 the trees and houses with which the islands are covered were strongly reflected with vivid and varied hues1 and the party hastened forward to enjoy the refreshment apparently proffered them2 but when they arrived1 the lake1 on whose bosom the images had floated--the trees1 amongst whose foliage they arose1 and the people who stood on the shore1 as if inviting their approach1 had all vanished1 and nothing remained but the uniform and irksome desert of sand and sky1 with a few naked and ragged ,arabs4 ,if ,m4 ,monge and his party had not been undeceived1 by actually going to the spot1 they would1 one and all1 have been firmly convinced that these visionary trees1 lakes1 and buildings had a real existence4 ,this kind of mirage is known in ,persia and ,arabia by the name of serab or miraculous water1 and in the western districts of ,india by that of scheram4 ,this illusion is the effect of unusual refraction1 and ,m4 ,faye attempts to account for the rose-coloured mountains by something of a similar nature4 ,it is right1 however1 to mention1 that learned astronomers do not consider this theory of any value4 ,lieutenant ,patterson1 one of the observers of the eclipse of #ahea1 says1 that ,it is very remarkable that the flames or prominences correspond exactly 7at least as far as he could judge7 with the spots on the sun's surface4 ,taking this statement with that of ,m4 ,faye1 it may be assumed1 as a new idea1 and nothing more1 that these prominences are1 after all1 mere aerial pictures of these openings in the sun's atmosphere1 or what are called sun spots4 ,in the ,edinburgh ,philosophical ,journal1 it is said1 that although it has lately been shown in the ,edinburgh ,observatory that it is possible to produce1 by certain optical experiments1 red flames on the sun's limb of precisely the rose-coloured tint described1 yet1 on weighing the whole of the evidence1 there does seem a great preponderance in favour of the eclipse flames being real appendages of the sun1 and in that case they must be masses of such vast size as to play no unimportant part in the economy of that stupendous orb4 ,during the last eclipse great disappointment was felt that the darkness was so insignificant1 although1 when we consider the enormous light-giving power of the sun1 and know that it was not wholly obscured1 we could hardly have expected any other result4 ,there can be no doubt that a decided change in the amount of light is only to be observed during a total eclipse of the sun1 one of which occurred on the #gth of ,september1 #aheh2 but1 unfortunately1 it was only visible in ,south ,america2 we must therefore content ourselves with the descriptions of those astronomers who can be fully relied on4 ,from the graphic account given by ,professor ,piazzi ,smyth1 the astronomer-royal for ,scotland1 ,page #ca of a total eclipse as seen by him on the western coast of ,norway1 we may form some notion of the imposing appearance of the surrounding country when obscured during the occurrence of this rare astronomical phenomenon4 ,the ,professor remarks1 ,to understand the scene more fully1 the reader must fancy himself on a small1 rocky island on a mountainous coast1 the weather calm1 and the sky at the beginning of the eclipse seven-tenths covered with thin and bright cirro-strati clouds4 ,as the eclipse approaches1 the clouds gradually darken1 the rays of the sun are no longer able to penetrate them through and through1 and drench them with living light as before1 but they become darker than the sky against which they are seen4 ,the air becomes sensibly colder1 the clouds still darker1 and the whole atmosphere murkier4 ,from moment to moment as the totality approaches1 the cold and darkness advance apace2 and there is something peculiarly and terribly convincing in the two different senses1 so entirely coinciding in their indications of an unprecedented fact being in course of accomplishment4 ,suddenly1 and apparently without any warning 7so immensely greater were its effects than those of anything else which had occurred71 the totality supervenes1 and darkness comes down4 ,then came into view lurid lights and forms1 as on the extinction of candles4 ,this was the most striking point of the whole phenomenon1 and made the ,norse peasants about us flee with precipitation1 and hide themselves for their lives4 ,darkness reigned everywhere in heaven and earth1 except where1 along the north-eastern horizon1 a narrow strip of unclouded sky presented a low burning tone of colour1 and where some distant snow-covered mountains1 beyond the range of the moon's shadow1 reflected the faint mono-chromatic light of the partially eclipsed sun1 and exhibited all the detail of their structure1 all the light1 and shade1 and markings of their precipitous sides with an apparently supernatural distinctness4 ,after a little time1 the eyes seemed to get accustomed to the darkness1 and the looming forms of objects close by could be discerned1 all of them exhibiting a dull-green hue2 seeming to have exhaled their natural colour1 and to have taken this particular one1 merely by force of the red colour in the north4 ,life and animation seemed1 indeed1 to have now departed from everything around1 and we could hardly but fear1 against our reason1 that if such a state of things was to last much longer1 some dreadful calamity must happen to us all2 while the lurid horizon1 northward1 appeared so like the gleams of departing light in some of the grandest paintings by ,danby and ,martin1 that we could not but believe1 in spite of the alleged extravagances of these artists1 that ,nature had opened up to the constant contemplation of their mind's-eye some of those magnificent revelations of power and glory which others can only get a glimpse of on occasions such as these4 ,it can be easily imagined1 that under such peculiar and awful circumstances1 the careful observation of these effects must be somewhat difficult1 ,page #cb and the only wonder is that the astronomical observations are conducted with any certainty at all4 ,in the eclipse of #ahdb1 it was not only the vivacious ,frenchman who was carried away in the impulse of the moment1 and had afterwards to plead that he was no more than a man as an excuse for his unfulfilled part in the observations1 but the same was the case with the grave ,englishman and the more stolid ,german4 ,in #ahea1 much the same failure in the observations occurred2 and on some person asking a worthy ,american1 who had come with his instruments from the other side of the world expressly to observe the eclipse1 what he had succeeded in doing8 he merely answered1 with much quiet impressiveness1 ,that if it was to be observed over again1 he hoped he would be able to do something1 but that1 as it was1 he had done nothing3 it had been too much for him4 ,this is not quite so bad as the fashionable lady who had been invited to look at an eclipse of the sun through a grand telescope1 but arriving too late1 inquired whether it could not be shown over again4 ,with this brief glance at the science of astronomy1 we once more return to the term gravity1 which will introduce to us some new and interesting facts1 under the head of what is called centre of gravity4 ,,chapter ,,iv4 ,,centre ,,of ,,gravity4 ,that point about which all the parts of a body do1 in any situation1 exactly balance each other4 ,the discovery of this fact is due to ,archimedes1 and it is a point in every solid body 7whatever the form may be7 in which the forces of gravity may be considered as united4 ,in our globe1 which is a sphere1 or rather an oblate spheroid1 the centre of gravity will be the centre4 ,thus1 if a plummet be suspended on the surface of the earth1 it points directly to the centre of gravity1 and1 consequently1 two plummet-lines suspended side by side cannot1 strictly speaking1 be parallel to each other4 ,if it were possible to bore or dig a gallery through the whole substance of the earth from pole to pole1 and then to allow a stone or the fabled ,mahomet's coffin to fall through it1 the momentum--i4e41 the force of the moving body1 would carry it beyond the centre of gravity4 ,this force1 however1 being exhausted1 there would be a retrograde movement1 and after many oscillations it would gradually come to rest1 and then1 unsupported by anything material1 it would be suspended by the force of gravitation1 and now enter into and take part in the general attracting force2 and being equally attracted on every side1 the stone or coffin must be totally without weight4 ,momentum is prettily illustrated by a series of inclined planes ,page #cc cut in mahogany1 with a grooved channel at the top1 in imitation of the famous ,russian ice mountains3 and if a marble is allowed to run down the ,page #cd first incline1 the momentum will carry it up the second1 from which it will again descend and pass up and down the third and last miniature mountain4 ,illustration3 ,fig4 #dj4 ,f4 ,the centre4 ,a ,b ,c ,d ,e4 ,plummet-lines1 all pointing to the centre1 and therefore diverging from each other4 ,illustration3 ,fig4 #da4 ,p ,p ,p4 ,inclined planes1 gradually decreasing in height1 cut out of inch mahogany1 with a groove at the top to carry an ordinary marble4 ,b ,b ,b4 ,different positions of the marble1 which starts from ,b ,a4 ,in a sphere of uniform density1 the centre of gravity is easily discovered1 but not so in an irregular mass2 and here1 perhaps1 an explanation of terms may not be altogether unacceptable4 ,mass1 is a term applied to solids1 such as a mass of lead or stone4 ,bulk1 to liquids1 such as a bulk of water or oil4 ,volume1 to gases1 such as a volume of air or oxygen4 ,illustration3 ,fig4 #db4 ,a ,b ,d1 ,the three points of suspension4 ,c1 ,the point of intersection1 and1 therefore1 the centre of gravity4 ,p1 ,the line of plummet4 ,to find the centre of gravity of any mass1 as1 for example1 an ordinary school-slate1 we must first of all suspend it from any part of the frame2 then allow a plumb-line to drop from the point of suspension1 and mark its direction on the slate4 ,again1 suspend the slate at various other points1 always marking the line of direction of the plummet1 and at the point where the lines intersect each other1 there will be the centre of gravity4 ,illustration3 ,fig4 #dc4 ,if the slate be now placed 7as shown in ,fig4 #dc7 on a blunt wooden point at the spot where the lines cross each other1 it will be found to balance exactly1 and this place is called the centre of gravity1 being the point with which all other particles of the body would move with parallel and equable motion during its fall4 ,the equilibrium of bodies is therefore much affected by the position of the centre of gravity4 ,thus1 if we cut out an elliptical figure from a board one inch in thickness1 and rest it on a flat surface by one of its edges 7as at ,no4 #a1 fig4 #dd71 this point of contact is called the point of support1 and the centre of gravity is immediately above it4 ,in this case1 the body is in a state of secure equilibrium1 for any motion on either side will cause the centre of gravity to ascend in these directions1 and an oscillation will ensue4 ,but if we place it upon the smaller end1 as shown at ,no4 #b 7fig4 #dd71 the position will be one of ,page #ce equilibrium1 but not stable or secure2 although the centre of gravity is directly above the point of support1 the slightest touch will displace the oval and cause its overthrow4 ,the famous story of ,columbus and the egg suggests a capital illustration of this fact2 and there are two modes in which the egg may be poised on either of the ends4 ,illustration3 ,fig4 #dd4 ,the point of support4 ,c1 ,the centre of gravity4 ,the one usually attributed to the great discoverer1 is that of scraping or slightly breaking away a little of the shell1 so as to flatten one of the ends1 thus-- ,illustration3 ,fig4 #de4 ,a ,represents the egg in its natural state1 and1 therefore1 in unstable equilibrium2 ,b1 another egg1 with the surface1 ,s1 flattened1 by which the centre of gravity is lowered1 and if not disturbed beyond the extent of the point of support the equilibrium is stable4 ,the most philosophical mode of making the egg stand on its end and without disturbing the exterior shell is to alter the position of the yolk1 which has a greater density than the white1 and is situated about the centre4 ,if the egg is now shaken so as to break the membrane enclosing the yolk1 and thus allow it to sink to the bottom of the smaller end1 the centre of gravity is lowered2 there is a greater proportion of weight ,page #cf concentrated in the small end1 and the egg stands erect1 as depicted at fig4 #df4 ,it is this variable position of the centre of gravity in ivory balls 7one part of which may be more dense than another7 that so frequently annoys even the best billiard-players2 and on this account a ball will deviate from the line in which it is impelled1 not from any fault of the player1 but in consequence of the ivory ball being of unequal density1 and1 therefore1 not having the centre corresponding with the centre of gravity4 ,a good billiard-player should1 therefore1 always try the ball before he engages to play for any large sum4 ,illustration3 ,fig4 #df4--,no4 #a4 ,section of egg4 ,c4 ,centre of gravity4 ,y4 ,the yolk4 ,w4 ,the white4 ,no4 #b4 ,c4 ,centre of gravity1 much lowered4 ,y4 ,the yolk at the bottom of the egg4 ,the toy called the tombola reminds us of the egg-experiment1 as there is usually a lump of lead inserted in the lower part of the hemisphere1 and when the toy is pushed down it rapidly assumes the upright position because the centre of gravity is not in the lowest place to which it can descend2 the latter position being only attained when the figure is upright4 ,illustration3 ,fig4 #dg4--,no4 #a4 ,c4 ,centre of gravity in the lowest place1 figure upright4 ,no4 #b4 ,c4 ,centre of gravity raised as the figure is inclined on either side1 but falling again into the lowest place as the figure gradually comes to rest4 ,there is a popular paradox in mechanics--viz41 a body having a tendency to fall by its own weight1 may be prevented from falling by adding to it a weight on the same side on which it tends to fall1 and the paradox is demonstrated by another well-known child's toy as depicted in the next cut4 ,page #cg ,illustration3 ,fig4 #dh4 ,the line of direction falling beyond the base2 the bent wire and lead weight throwing the centre of gravity under the table and near the leaden weight2 the hind legs become the point of support1 and the toy is perfectly balanced4 ,illustration3 ,fig4 #di4--,no4 #a4 ,sword balanced on handle3 the arc from ,c to ,d is very small1 and if the centre1 ,c1 falls out of the line of direction it is not easily restored to the upright position4 ,no #b4 ,sword balanced on the point3 the arc from ,c to ,d much larger1 and therefore the sword is more easily balanced4 ,after what has been explained regarding the improvement of the stability of the egg by lowering the situation of the centre of gravity1 it may at first appear singular that a stick loaded with a weight at its upper extremity can be balanced perpendicularly with greater ease and precision than when the weight is lower down and nearer the hand2 and that a sword can be balanced best when the hilt is uppermost2 ,page #ch but this is easily explained when it is understood that with the handle downwards a much smaller arc is described as it falls than when reversed1 so that in the former case the balancer has not time to re-adjust the centre1 whilst in the latter position the arc described is so large that before the sword falls the centre of gravity may be restored within the line of direction of the base4 ,illustration3 ,fig4 #ej4--,no4 #a4 ,the two pieces of mahogany1 carved to represent a man and a boy1 one being #aj and the other #e inches long1 attached to board by hinges at ,h ,h4 ,illustration3 ,fig4 #ea4--,no4 #b4 ,the board pushed forward1 striking against a nail1 when the short piece falls first1 and the long one second4 ,for the same reason1 a child tripping against a stone will fall quickly2 whereas1 a man can recover himself2 this fact can be very nicely shown by fixing two square pieces of mahogany of different lengths1 by hinges on a flat base or board1 then if the board be pushed rapidly forward and struck against a lead weight or a nail put in the ,page #ci table1 the short piece is seen to fall first and the long one afterwards2 the difference of time occupied in the fall of each piece of wood 7which may be carved to represent the human figure7 being clearly denoted by the sounds produced as they strike the board4 ,boat-accidents frequently arise in consequence of ignorance on the subject of the centre of gravity1 and when persons are alarmed whilst sitting in a boat1 they generally rise suddenly1 raise the centre of gravity1 which falling1 by the oscillation of the frail bark1 outside the line of direction of the base1 cannot be restored1 and the boat is upset2 if the boat were fixed by the keel1 raising the centre of gravity would be of little consequence1 but as the boat is perfectly free to move and roll to one side or the other1 the elevation of the centre of gravity is fatal1 and it operates just as the removal of the lead would do1 if changed from the base to the head of the tombola toy4 ,a very striking experiment1 exhibiting the danger of rising in a boat1 may be shown by the following model1 as depicted at ,nos4 #a and #b1 figs4 #eb and #ec4 ,illustration3 ,fig4 #eb4--,no4 #a4 ,sections of a toy-boat floating in water4 ,b ,b ,b4 ,three brass wires placed at regular distances and screwed into the bottom of the boat1 with cuts or slits at the top so that when the leaden bullets1 ,l ,l ,l1 which are perforated and slide upon them like beads1 are raised to the top1 they are retained by the brass cuts springing out2 when the bullets are at the bottom of the lines they represent persons sitting in a boat1 as shown in the lower cuts1 and the centre of gravity will be within the vessel4 ,we thus perceive that the stability of a body placed on a base depends upon the position of the line of direction and the height of the centre of gravity4 ,security results when the line of direction falls within the base4 ,instability when just at the edge4 ,incapability of standing when falling without the base4 ,page #dj ,illustration3 ,fig4 #ec4--,no4 #b4 ,the leaden bullets raised to the top now show the result of persons suddenly rising1 when the boat immediately turns over1 and either sinks or floats on the surface with the keel upwards4 ,illustration3 ,fig4 #ed4 ,f4 ,board cut and painted to represent the leaning-tower of ,pisa4 ,g4 ,the centre of gravity and plummet line suspended from it4 ,h4 ,the hinge which attaches it to the base board4 ,i4 ,the string1 sufficiently long to unwind and allow the plummet to hang outside the base1 so that1 when cut1 the model falls in the direction of the arrow4 ,the leaning-tower of ,pisa is one hundred and eighty-two feet in height1 and is swayed thirteen and a half feet from the perpendicular1 but yet remains perfectly firm and secure1 as the line of direction falls considerably within the base4 ,if it was of a greater altitude it could no longer stand1 because the centre of gravity would be so elevated that the line of direction would fall outside the base4 ,this fact may be illustrated by taking a board several feet in length1 and having cut ,page #da it out to represent the architecture of the leaning-tower of ,pisa1 it may then be painted in distemper1 and fixed at the right angle with a hinge to another board representing the ground1 whilst a plumb-line may be dropped from the centre of gravity2 and it may be shown that as long as the plummet falls within the base1 the tower is safe2 but directly the model tower is brought a little further forward by a wedge so that the plummet hangs outside1 then1 on removing the support1 which may be a piece of string to be cut at the right moment1 the model falls1 and the fact is at once comprehended4 ,the leaning-towers of ,bologna are likewise celebrated for their great inclination2 so also 7in ,england7 is the hanging-tower1 or1 more correctly1 the massive wall which has formed part of a tower at ,bridgenorth1 ,salop2 it deviates from the perpendicular1 but the centre of gravity and the line of direction fall within the base1 and it remains secure2 indeed1 so little fears are entertained of its tumbling down1 that a stable has been erected beneath it4 ,illustration3 ,fig4 #ee4--,no4 #a4 ,two billiard-cues arranged for the experiment and fixed to a board3 the ball is rolling up4 ,no4 #b4 ,sections showing that the centre of gravity1 ,c1 is higher at ,a than at ,b1 which represents the thick end of the cues2 it therefore1 in effect1 rolls down hill4 ,one of the most curious paradoxes is displayed in the ascent of a billiard-ball from the thin to the thick ends of two billiard-cues placed at an angle1 as in our drawing above2 here the centre of gravity is raised at starting1 and the ball moves in consequence of its actually falling from the high to the low level4 ,much of the stability of a body depends on the height through which the centre of gravity must be elevated before the body can be overthrown4 ,the greater this height1 the greater will be the immovability of the mass4 ,one of the grandest examples of this fact is shown in the ancient ,pyramids2 and whilst gigantic palaces1 with vast columns1 ,page #db and all the solid grandeur belonging to ,egyptian architecture1 have succumbed to time and lie more or less prostrate upon the earth1 the ,pyramids1 in their simple form and solidity1 remain almost as they were built1 and it will be noticed1 in the accompanying sketch1 how difficult1 if not impossible1 it would be to attempt to overthrow bodily one of these great monuments of ancient times4 ,illustration3 ,fig4 #ef4 ,c4 ,centre of gravity1 which must be raised to ,d before it can be overthrown4 ,illustration3 ,fig4 #eg4 ,no4 #a4 ,the centre of gravity is near the ground1 and falls within the wheels4 ,no4 #b4 ,the centre of gravity is much elevated1 and the line of direction is outside the wheels4 ,the principles already explained are directly applicable to the construction or secure loading of vehicles2 and in proportion as the centre of gravity is elevated above the point of support 7that is1 the wheels71 so is the insecurity of the carriage increased1 and the contrary takes place if the centre of gravity is lowered4 ,again1 if a waggon be loaded ,page #dc with a very heavy substance which does not occupy much space1 such as iron1 lead1 or copper1 or bricks1 it will be in much less danger of an overthrow than if it carries an equal weight of a lighter body1 such as pockets of hops1 or bags of wool or bales of rags4 ,in the one instance1 the centre of gravity is near the ground1 and falls well within the base1 as at ,no4 #a1 fig4 #eg4 ,in the other1 the centre of gravity is considerably elevated above the ground1 and having met with an obstruction which has raised one side higher than the other1 the line of direction has fallen outside the wheels1 and the waggon is overturning as at ,no4 #b4 ,the various postures of the human body may be regarded as so many experiments upon the position of the centre of gravity which we are every moment unconsciously performing4 ,to maintain an erect position1 a man must so place his body as to cause the line of direction of his weight to fall within the base formed by his feet4 ,illustration3 ,fig4 #eh4 ,the more the toes are turned outwards1 the more contracted will be the base1 and the body will be more liable to fall backwards or forwards2 and the closer the feet are drawn together1 the more likely is the body to fall on either side4 ,the acrobats1 and so-called ,india-,rubber ,brothers1 dancing dogs1 c41 unconsciously acquire the habit of accurately balancing themselves in all kinds of strange positions2 but as these accomplishments are not to be recommended to young people1 some other marvels 7such as balancing a pail of water on a stick laid upon a table7 may be adduced1 as illustrated in fig4 #ei4 ,let ,a ,b represent an ordinary table1 upon which place a broomstick1 ,c ,d1 so that one-half shall lay upon the table and the other extend from ,page #dd it2 place over the stick the handle of an empty pail 7which may possibly require to be elongated for the experiment7 so that the handle touches or falls into a notch at ,h2 and in order to bring the pail well under the table1 another stick is placed in the notch ,e1 and is arranged in the line ,g ,f ,e1 one end resting at ,g and the other at ,e4 ,having made these preparations1 the pail may now be filled with water2 and although it appears to be a most marvellous result1 to see the pail apparently balanced on the end of a stick which may easily tilt up1 the principles already explained will enable the observer to understand that the centre of gravity of the pail falls within the line of direction shown by the dotted line2 and it amounts in effect to nothing more than carrying a pail on the centre of a stick1 one end of which is supported at ,e1 and the other through the medium of the table1 ,a ,b4 ,illustration3 ,fig4 #ei4 ,this illustration may be modified by using a heavy weight1 rope1 and stick1 as shown in our sketch below4 ,illustration3 ,fig4 #fj4 ,before we dismiss this subject it is advisable to explain a term referring to a very useful truth1 called the centre of percussion2 a knowledge of which1 gained instinctively or otherwise1 enables the workman to wield his tools with increased power1 and gives greater force to the cut of the swordsman1 so that1 with some physical strength1 he may perform the feat of cutting a sheep in half1 cleaving a bar of lead1 or ,page #de neatly dividing1 la ,saladin1 in ancient ,saracen fashion1 a silk handkerchief floating in the air4 ,there is a feat1 however1 which does not require any very great strength1 but is sufficiently startling to excite much surprise and some inquiry--viz41 the one of cutting in half a broomstick supported at the ends on tumblers of water without spilling the water or cracking or otherwise damaging the glass supports4 ,illustration3 ,fig4 #fa4 ,these and other feats are partly explained by reference to time3 the force is so quickly applied and expended on the centre of the stick that it is not communicated to the supports2 just as a bullet from a pistol may be sent through a pane of glass without shattering the whole square1 but making a clean hole through it1 or a candle may be sent through a plank1 or a cannon-ball pass through a half opened door without causing it to move on its hinges4 ,but the success of the several feats depends in a great measure on the attention that is paid to the delivery of the blows at the centre of percussion of the weapon2 this is a point in a moving body where the percussion is the greatest1 and about which the impetus or force of all parts is balanced on every side4 ,it may be better understood by reference to our drawing below4 ,applying this principle to a model sword made of wood1 cut in half in the centre of the blade1 and then united with an elbow-joint1 the handle being fixed to a board by a wire passed through it and the two upright pieces of wood1 the fact is at once apparent1 and is well shown in ,nos4 #a1 #b1 #c1 fig4 #fb4 ,page #df ,illustration3 ,fig4 #fb4 ,no4 #a1 is the wooden sword1 with an elbow-joint at ,c4 ,no4 #b4 ,sword attached to board at ,k1 and being allowed to fall from any angle shown by dotted-line1 it strikes the block1 ,w1 outside the centre of percussion1 ,p1 and as there is unequal motion in the parts of the sword it bends down 7or1 as it were1 breaks7 at the elbow-joint1 ,c4 ,no4 #c displays the same model2 but here the blow has fallen on the block1 ,w1 precisely at the centre of percussion of the sword1 ,p1 and the elbow-joint remains perfectly firm4 ,when a blow is not delivered with a stick or sword at the centre of percussion1 a peculiar jar1 or what is familiarly spoken of as a stinging sensation1 is apparent in the hand2 and the cause of this disagreeable result is further elucidated by fig4 #fc1 in which the post1 ,a1 corresponds with the handle of the sword4 ,page #dg ,illustration3 ,fig4 #fc4 ,a4 ,the post to which a rope is attached4 ,b and ,c are two horses running round in a circle1 and it is plain that ,b will not move so quick as ,c1 and that the latter will have the greatest moving force2 consequently1 if the rope was suddenly checked by striking against an object at the centre of gravity1 the horse ,c would proceed faster than ,b1 and would impart to ,b a backward motion1 and thus make a great strain on the rope at ,a4 ,but if the obstacle were placed so as to be struck at a certain point nearer ,c1 viz41 at or about the little star1 the tendency of each horse to move on would balance and neutralize the other1 so that there would be no strain at ,a4 ,the little star indicates the centre of percussion4 ,all military men1 and especially those young gentlemen who are intended for the army1 should bear in mind this important truth during their sword-practice2 and with one of ,mr4 ,wilkinson's swords1 made only of the very best steel1 they may conquer in a chance combat which might otherwise have proved fatal to them4 ,to ,mr4 ,wilkinson1 of ,pall ,mall1 the eminent sword-cutler1 is due the great merit of improving the quality of the steel employed in the manufacture of officers' swords2 and with one of his weapons1 the author has repeatedly thrust through an iron plate about one-eighth of an inch in thickness without injuring the point1 and has also bent one nearly double without fracturing it1 the perfect elasticity of the steel bringing the sword straight again4 ,these1 and other severe tests applied to ,wilkinson's swords1 show that there is no reason why an officer should not possess a weapon that will bear comparison with1 nay1 surpass1 the far-famed ,toledo weapon1 instead of submitting to mere army-tailor swords1 which are often little better than hoops of beer barrels2 and1 in dire combat with ,hindoo or ,mussulman fanatics' ,tulwah1 may show too late the folly of the owner4 ,illustration3 ,fig4 #fd4 ,page #dh ,,chapter ,v4 ,,specific ,,gravity4 ,it is recorded of the great ,dr4 ,wollaston1 that when ,sir ,humphry ,davy placed in his hand1 what was then considered to be the scientific wonder of the day--viz41 a small bit of the metal potassium1 he exclaimed at once1 ,how heavy it is1 and was greatly surprised1 when ,sir ,humphry threw the metal on water1 to see it not only take fire1 but actually float upon the surface2 here1 then1 was a philosopher possessing the deepest learning1 unable1 by the sense of touch and by ordinary handling1 to state correctly whether the new substance 7and that a metal71 was heavy or light2 hence it is apparent that the property of specific gravity is one of importance1 and being derived from the ,latin1 means species1 a particular sort or kind2 and gravis1 heavy or weight--i4e41 the particular weight of every substance compared with a fixed standard of water4 ,illustration3 ,fig4 #fe4 ,a4 ,a large cylindrical vessel containing water1 in which the egg sinks till it reaches the bottom of the glass4 ,b4 ,a similar glass vessel containing half brine and half water1 in which the egg floats in the centre--viz41 just at the point where the brine and water touch4 ,we are so constantly in the habit of referring to a standard of perfection in music and the arts of painting and sculpture1 that the youngest will comprehend the office of water when told that it is the philosopher's unit or starting-point for the estimation of the relative weights of solids and liquids4 ,a good idea of the scope and meaning of the term specific gravity1 is acquired by a few simple experiments1 thus3 if a cylindrical ,page #di glass1 say eighteen inches long1 and two and a half wide1 is filled with water1 and another of the same size is also filled1 one half with water and the other half with a saturated solution of common salt1 or what is commonly termed brine1 a most amusing comparison of the relative weights of equal bulks of water and brine1 can be made with the help of two eggs2 when one of the eggs is placed in the glass containing water1 it immediately sinks to the bottom1 showing that it has a greater specific gravity than water2 but when the other egg is placed in the second glass containing the brine1 it sinks through the water till it reaches the strong solution of salt1 where it is suspended1 and presents a most curious and pretty appearance2 seeming to float like a balloon in air1 and apparently suspended upon nothing1 it provokes the inquiry1 whether magnetism has anything to do with it8 ,the answer1 of course1 is in the negative1 it merely floats in the centre1 in obedience to the common principle1 that all bodies float in others which are heavier than themselves2 the brine has1 therefore1 a greater weight than an equal bulk of water1 and is also heavier than the egg4 ,a pleasing sequel to this experiment may be shown by demonstrating how the brine is placed in the vessel without mixing with the water above it2 this is done by using a glass tube and funnel1 and after pouring away half the water contained in the vessel 7,fig4 #fe471 the egg can be floated from the bottom to the centre of the glass1 by pouring the brine down the funnel and tube4 ,the saturated solution of salt remains in the lower part of the vessel and displaces the water1 which floats upon its surface like oil on water1 carrying the egg with it4 ,illustration3 ,fig4 #ff4 ,a vessel half full of water1 and as the brine is poured down the tube the egg gradually rises4 ,the water of the ,dead ,sea is said to contain about twenty-six per cent4 of saline matter1 which chiefly consists of common salt4 ,it is perfectly clear and bright1 and in consequence of the great density1 a person may easily float on its surface1 like the egg on the brine1 so that if a ship could be heavily laden whilst floating on the water of the ,dead ,sea1 it would most likely sink if transported to the ,thames4 ,this illustration of specific gravity is also shown by a model ship1 which being first floated on the brine1 will afterwards sink if conveyed to another vessel containing water4 ,one of the tin model ships sold as a magnetic ,page #ej toy answers nicely for this experiment1 but it must be weighted or adjusted so that it just floats in the brine1 ,a2 then it will sink1 when placed1 in another vessel containing only water4 ,illustration3 ,fig4 #fg4 ,a4 ,vessel containing brine1 upon which the little model floats4 ,b4 ,vessel containing water1 in which the ship sinks4 ,another amusing illustration of the same kind is displayed with goldfish1 which swim easily in water1 floating on brine1 but cannot dive to the bottom of the vessel1 owing to the density of the saturated solution of salt4 ,if the fish are taken out immediately after the experiment1 and placed in fresh water1 they will not be hurt by contact with the strong salt water4 ,these examples of the relative weights of equal bulks1 enable the youthful mind to grasp the more difficult problem of ascertaining the specific gravity of any solid or liquid substance2 and here the strict meaning of terms should not be passed by4 ,specific weight must not be confounded with ,absolute weight2 the latter means the entire amount of ponderable matter in any body3 thus1 twenty-four cubic feet of sand weigh about one ton1 whilst specific weight means the relation that subsists between the absolute weight and the volume or space which that weight occupies4 ,thus a cubic foot of water weighs sixty-two and a half pounds1 or #ajjj ounces avoirdupois1 but changed to gold1 the cubic foot weighs more than half a ton1 and would be equal to about #ai1cjj ounces--hence the relation between the cubic foot of water and that of ,page #ea gold is nearly as #a to #ai4c2 the latter is therefore called the specific gravity of gold4 ,such a mode of taking the specific gravity of different substances--viz41 by the weight of equal bulks1 whether cubic feet or inches1 could not be employed in consequence of the difficulty of procuring exact cubic inches or feet of the various substances which by their peculiar properties of brittleness or hardness would present insuperable obstacles to any attempt to fashion or shape them into exact volumes4 ,it is therefore necessary to adopt the method first devised by ,archimedes1 #fjj ,b4,c41 when he discovered the admixture of another metal with the gold of ,king ,hiero's crown4 ,this amusing story1 ending in the discovery of a philosophical truth1 may be thus described3--,king ,hiero gave out from the royal treasury a certain quantity of gold1 which he required to be fashioned into a crown2 when1 however1 the emblem of power was produced by the goldsmith1 it was not found deficient in weight1 but had that appearance which indicated to the monarch that a surreptitious addition of some other metal must have been made4 ,it may be assumed that ,king ,hiero consulted his friend and philosopher ,archimedes1 and he might have said1 ,tell me1 ,archimedes1 without pulling my crown to pieces1 if it has been adulterated with any other metal8 ,the philosopher asked for time to solve the problem1 and going to take his accustomed bath1 discovered then specially what he had never particularly remarked before--that1 as he entered the vessel of water1 the liquid rose on each side of him--that he1 in fact1 displaced a certain quantity of liquid4 ,thus1 supposing the bath to have been full of water1 directly ,archimedes stepped in1 it would overflow4 ,let it be assumed that the water displaced was collected1 and weighed #ij pounds1 whilst the philosopher had weighed1 say #bjj pounds4 ,now1 the train of reasoning in his mind might be of this kind3--,my body displaces #ij pounds of water2 if ,i had an exact cast of it in lead1 the same bulk and weight of liquid would overflow2 but the weight of my body was1 say #bjj pounds1 the cast in lead #ajjj pounds2 these two sums divided by #ij would give very different results1 and they would be the specific gravities1 because the rule is thus stated3--',divide the gross weight by the loss of weight in water1 the water displaced1 and the quotient gives the specific gravity4' ,the rule is soon tested with the help of an ordinary pair of scales1 and the experiment made more interesting by taking a model crown of some metal1 which may be nicely gilt and burnished by ,messrs4 ,elkington1 the celebrated electro-platers of ,birmingham4 ,for convenience1 the pan of one scale is suspended by shorter chains than the other1 and should have a hook inserted in the middle2 upon this is placed the crown1 supported by very thin copper wire4 ,for the sake of argument1 let it be supposed that the crown weighs #ag ounces avoirdupois1 which are duly placed in the other scale-pan1 and without touching these weights1 the crown is now placed in a vessel of water4 ,it might be supposed that directly the crown enters the water1 it would gain weight1 in consequence of being wetted1 ,page #eb but the contrary is the case1 and by thrusting the crown into the water1 it may be seen to rise with great buoyancy so long as the #ag ounces are retained in the other scale-pan2 and it will be found necessary to place at least two ounces in the scale-pan to which the crown is attached before the latter sinks in the water2 and thus it is distinctly shown that the crown weighs only about #ae ounces in the water1 and has therefore lost instead of gaining weight whilst immersed in the liquid4 ,the rule may now be worked out3 ,ounces4 ,weight of crown in air #ag ,ditto in water #ae --- ,less in water #b #ag _/ #b #h ,the quotient #h demonstrates that the crown is manufactured of copper1 because it would have been about #ai if made of pure gold4 ,illustration3 ,fig4 #fh4 ,a4 ,ordinary pair of scales4 ,b4 ,scale-pan1 containing #ag ounces1 being the weight of the crown in air4 ,c4 ,pan1 with hook and crown attached1 which is sunk in the water contained in the vessel ,d2 this pan contains the two ounces1 which must be placed there to make the crown sink and exactly balance ,b4 ,page #ec ,table of the ,specific ,gravities of the ,metals in common use4 ,platinum #bj4ih ,gold #ai4bf to #ai4c and #ai4fd ,mercury #ac4eg ,lead #aa4ce ,silver #aj4dg to #aj4e ,bismuth #i4hb ,copper #h4hi ,iron #g4gi ,tin #g4bi ,zinc #f4e to #g4d ,the simple rule already explained may be applied to all metals of any size or weight1 and when the mass is of an irregular shape1 having various cavities on the surface1 there may be some difficulty in taking the specific gravity1 in consequence of the adhesion of air-bubbles2 but this may be obviated either by brushing them away with a feather1 or1 what is frequently much better1 by dipping the metal or mineral first into alcohol1 and then into water1 before placing it in the vessel of water1 by which the actual specific gravity is to be taken4 ,the mode of taking the specific gravity of liquids is very simple1 and is usually performed in the laboratory by means of a thin globular bottle which holds exactly #ajjj grains of pure distilled water at #fj ,fahrenheit4 ,a little counterpoise of lead is made of the exact weight of the dry globular bottle1 and the liquid under examination is poured into the bottle and up to the graduated mark in the neck2 the bottle is then placed in one scale-pan1 the counterpoise and the #ajjj-;grain weight in the other2 if the liquid 7such as oil of vitriol7 is heavier than water1 then more weight will be required--viz41 #hde grains--and these figures added to the #ajjj would indicate at once that the specific gravity of oil of vitriol was #a4hde as compared with water1 which is #a4jjj4 ,when the liquid1 such as alcohol1 is lighter than water1 the #ajjj-;grain weight will be found too much1 and grain weights must be added to the same scale-pan in which the bottle is standing1 until the two are exactly balanced4 ,if ordinary alcohol is being examined1 it will be found necessary to place #ahj grains with the bottle1 and these figures deducted from the #ajjj grains in the other scale-pan1 leave #hbj1 which1 marked with a dot before the first figure 7sic 4#hbj71 indicates the specific gravity of alcohol to be less than that of water4 ,the difference in the gravities of various liquids is displayed in a very pleasing manner by an experiment devised by ,professor ,griffiths1 to whom chemical lecturers are especially indebted for some of the most ingenious and beautiful illustrations which have ever been devised4 ,the experiment consists in the arrangement of five distinct liquids of various densities and colours1 the one resting on the other1 and distinguished not only by the optical line of demarcation1 but by little balls of wax1 which are adjusted by leaden shot inside1 so as to sink through ,page #ed the upper strata of liquids1 and rest only upon the one that it is intended to indicate4 ,the manipulation for this experiment is somewhat troublesome1 and is commenced by procuring some pure bright quicksilver1 upon which an iron bullet 7black-leaded1 or painted of any colour7 is placed1 or one of those pretty glass balls which are sold in such quantities at the ,crystal ,palace4 ,secondly4 ,put as much white vitriol 7sulphate of zinc7 into a half pint of boiling water as it will dissolve1 and1 when cold1 pour off the clear liquid1 make up a ball of coloured wax 7say red71 and adjust it by placing little shot inside1 until it sinks in a solution of sulphate of copper and floats on that of the white vitriol4 ,thirdly4 ,make a solution of sulphate of copper in precisely the same manner1 and adjust another wax ball to sink in water1 and float on this solution4 ,fourthly4 ,some clear distilled water must be provided4 ,fifthly4 ,a little cochineal is to be dissolved in some common spirits of wine 7alcohol71 and a ball of cork painted white provided4 ,finally4 ,a long cylindrical glass1 at least eighteen inches high1 and two and a half or three inches diameter1 must be made to receive these five liquids1 which are arranged in their proper order of specific gravity by means of a long tube and funnel4 ,the four balls--viz41 the iron1 the two wax1 and the cork balls1 are allowed to slide down the long glass1 which is inclined at an angle2 and then1 by means of the tube and funnel1 pour in the tincture of cochineal1 and all the balls will remain at the bottom of the glass4 ,the water is poured down next1 and now the cork ball floats up on the water1 and marks the boundary line of the alcohol and water4 ,then the solution of blue vitriol1 when a wax ball floats upon it4 ,thirdly1 the solution of white vitriol1 upon which the second wax ball takes its place2 and lastly1 the quicksilver is poured down the tube1 and upon this heavy metallic fluid the iron or glass ball floats like a cork on water4 ,illustration3 ,fig4 #fi4 ,long cylindrical glass1 #ah #c inches1 containing the five liquids4 ,the tube may now be carefully removed1 pausing at each liquid1 so that no mixture take place between them2 and the result is the arrangement of five liquids1 giving the appearance of a cylindrical glass painted with ,page #ee bands of crimson1 blue1 and silver2 and the liquids will not mingle with each other for many days4 ,a more permanent arrangement can be devised by using liquids which have no affinity1 or will not mix with each other--such as mercury1 water1 and turpentine4 ,the specific weight or weights of an equal measure of air and other gases is determined on the same principle as liquids1 although a different apparatus is required4 ,a light capped glass globe1 with stop-cock1 from #ej to #ajj cubic inches capacity1 is weighed full of air1 then exhausted by an air-pump1 and weighed empty1 the loss being taken as the weight of its volume of air2 these figures are carefully noted1 because air instead of water is the standard of comparison for all gases4 ,when the specific gravity of any other gas is to be taken1 the glass globe is again exhausted1 and screwed on to a gas jar provided with a proper stop-cock1 in which the gas is contained2 and when perfect accuracy is required1 the gas must be dried by passing it over some asbestos moistened with oil of vitriol1 and contained in a glass tube1 and the gas jar should stand in a mercurial trough4 7,fig4 #gj47 ,the stop-cocks are gradually turned1 and the gas admitted to the exhausted globe from the gas jar2 when full1 the cocks are turned off1 the globe unscrewed1 and again weighed1 and by the common rule of proportion1 as the weight of the air first found is to the weight of the gas1 so is unity 7#a4jjj1 the density of air7 to a number which expresses the density of the gas required4 ,if oxygen had been the gas tried1 the number would be #a4aaa1 being the specific gravity of that gaseous element4 ,if chlorine1 #b4dgj4 ,carbonic acid1 #a4ejj4 ,hydrogen being much less than air1 the number would only be #fi1 or decimally #j4jfi4 ,illustration3 ,fig4 #gj4 ,a4 ,glass globe to contain the gas4 ,b4 ,gas jar standing in the mercurial trough1 ,d4 ,c4 ,tube containing asbestos moistened with oil of vitriol4 ,a very good approximation to the correct specific gravity 7particularly where a number of trials have to be made with the same gas1 such as ,page #ef ordinary coal gas7 is obtained by suspending a light paper box1 with holes at one end1 on one arm of a balance1 and a counterpoise on the other4 ,the box can be made carefully1 and should have a capacity equal to a half or quarter cubic foot2 it is suspended with the holes downward1 and is filled by blowing in the coal gas until it issues from the apertures1 and can be recognised by the smell4 ,the rule in this case would be equally simple3 as the known weight of the half or quarter cubic foot of common air is to the weight of the coal gas1 so is #a4jjj to the number required4 7,fig4 #ga47 ,illustration3 ,fig4 #ga4 ,a4 ,the balance4 ,b4 ,the paper box1 of a known capacity4 ,c4 ,gas-pipe blowing in coal-gas1 the arrows showing entrance of gas and exit of the air4 ,as an illustration of the different specific weights of the gases1 a small balloon1 containing a mixture of hydrogen and air1 may be so adjusted that it will just sink in a tall glass shade inverted and supported on a pad made of a piece of oilcloth shaped round and bound with list4 ,on passing in quickly a large quantity of carbonic acid1 the little balloon will float on its surface2 and if another balloon1 containing only hydrogen1 is held in the top part of the open shade1 and a sheet of glass carefully slid over the open end1 the density of the gases 7although they are perfectly invisible7 is perfectly indicated2 and1 as a climax to the experiment1 a third balloon can be filled with laughing gas1 and may be placed in the glass shade1 taking care that the one full of pure hydrogen does not escape2 the last balloon will sink to the bottom of the ,page #eg jar1 because laughing gas is almost as heavy as carbonic acid1 and the weight of the balloon will determine its descent4 7,fig4 #gb47 ,illustration3 ,fig4 #gb4 ,inverted large glass shade1 containing half carbonic acid and half common air4 ,illustration3 ,fig4 #gc4 ,a4 ,inverted glass shade1 containing the material1 ,b1 for generating carbonic acid gas4 ,c4 ,the soap-bubble4 ,d ,d4 ,the glass tube for blowing the bubbles4 ,e4 ,small lantern1 to throw a bright beam of light from the oxy-hydrogen jet upon the thin soap-bubble1 which then displays the most beautiful iridescent colours4 ,a soap-bubble will rest most perfectly on a surface of carbonic acid gas1 and the aerial and elastic cushion supports the bubble till it bursts4 ,the experiment is best performed by taking a glass shade twelve inches broad and deep in proportion1 and resting it on a pad2 half a pound of sesquicarbonate of soda is then placed in the vessel1 and upon this is poured a mixture of half a pint of oil of vitriol and half a pint of water1 the latter being previously mixed and allowed to cool before use4 ,an enormous quantity of carbonic acid gas is suddenly generated1 and rising to the edge1 overflows at the top of the glass shade4 ,a well-formed soap-bubble1 detached neatly from the end of a glass-tube1 oscillates gently on the surface of the heavy gas1 and presents a most curious and pleasing appearance4 ,the soapy water is prepared by cutting a few pieces of yellow soap1 and placing them in a two-ounce bottle containing distilled water4 7,fig4 #gc47 ,the specific gravity of the gases1 may therefore be either greater1 or less than atmospheric air1 ,page #eh which has been already mentioned as the standard of comparison1 and examined by this test the vapours of some of the compounds of carbon and hydrogen are found to possess a remarkably high gravity2 in proof of which1 the vapour of ether may be adduced as an example1 although it does not consist only of the two elements mentioned1 but contains a certain quantity of oxygen4 ,in a cylindrical tin vessel1 two feet high and one foot in diameter1 place an ordinary hot-water plate1 of course full of boiling water2 upon this warm surface pour about half an ounce of the best ether2 and1 after waiting a few minutes until the whole is converted into vapour1 take a syphon made of half-inch pewter tube1 and warm it by pouring through it a little hot water1 taking care to allow the water to drain away from it before use4 ,after placing the syphon in the tin vessel1 a light may be applied to the extremity of the long leg outside the tin vessel1 to show that no ether is passing over until the air is sucked out as with the water-syphon2 and after this has been done1 several warm glass vessels may be filled with this heavy vapour of ether1 which burns on the application of flame4 ,finally1 the remainder of the vapour may be burnt at the end of the syphon tube1 demonstrating in the most satisfactory manner that the vapour is flowing through the syphon just as spirit is removed by the distillers from the casks into cellars of the public-houses4 7,fig4 #gd47 ,illustration3 ,fig4 #gd4 ,a4 ,tin vessel containing the hot-water plate1 ,b1 upon which the ether is poured4 ,c4 ,the syphon4 ,d4 ,glass to receive the vapour4 ,e4 ,combustion of the ether vapour in another vessel4 ,page #ei ,before dismissing the important subject of specific gravity 7or1 as it is termed by the ,french savants1 density71 it may be as well to state that astronomers have been enabled1 by taking the density of the earth and by astronomical observations1 to calculate the gravity of the planets belonging to our solar system2 and it is interesting to observe that the density of the planet ,venus is the only one approaching the gravity of the earth3-- ,the ,earth #a4jjj ,the ,sun 4#bed ,the ,moon 4#gdb ,mercury #b4ehc ,venus #a4jcg ,mars 4#fej ,jupiter 4#beh ,saturn 4#ajd ,herschel 4#bbj ,,chapter ,,vi4 ,,attraction ,,of ,,cohesion4 ,in previous chapters one kind of attraction--viz41 that of gravitation1 has been discussed and illustrated in a popular manner1 and pursuing the examination of the invisible1 active1 and real forces of nature1 the attraction of cohesion will next engage our attention4 ,there is a peculiar satisfaction in pursuing such investigations1 because every step is attended by a reasonable proof2 there is no ghostly mystery in philosophic studies2 the mind is not suddenly startled at one moment with that which seems more than natural2 it is not carried away in an ecstasy of wonder and awe1 as in the so-called spirit-rapping experiments1 to be again rudely brought back to the material by the disclosure of trickeries of the most ludicrous kind1 such as those lately exposed by ,m4 ,jobert de ,lamballe1 at the ,academy of ,sciences at ,paris4 ,this gentleman has unmasked the effrontery of the spirit-rappers by merely stripping the stocking from the heel of a young girl of fourteen4 ,m4 ,velpeau declares that the rapping is produced by the muscles of the heel and knee acting in concert1 and quotes the case of a lady once celebrated as a medium1 who has the power of producing the most curious and interesting music with the tendons of the thigh4 ,this music is said to be loud enough to be heard from one end of a long room to the other1 and has often played a conspicuous part in the revelations made by the medium4 ,m4 ,jules ,clocquet also explained the method by which the famous girl pendulum had so long abused the credulity of the ,paris public4 ,this girl1 whose self-styled faculty is that of striking the hour at any time of the day or night1 was attended at the ,hospital ,st4 ,louis by ,m4 ,clocquet1 who states that the vibrations in ,page #fj this case were produced by a rotatory motion in the lumbar regions of the vertebral column4 ,the sound of these 7 la rattlesnake7 was so powerful1 that they might be distinctly heard at a distance of twenty-five feet4 ,in studying the powers of nature1 which the most sceptical mind allows must exist1 there is an abundant field for experiment without attempting the exploits of ,macbeth's witches1 or the fanciful powers of ,manfred2 and1 returning to the theme of our present chapter1 it may be asked1 how is cohesion defined8 and the answer may be given1 by directing attention to the three physical conditions of water1 which assumes the form of ice1 water1 or steam4 ,in the ,polar regions1 and also in the ,alpine and other mountains where glaciers exist1 there the traveller speaks of ice twenty1 thirty1 forty1 nay1 three hundred feet in thickness4 ,here the withdrawal of a certain quantity of heat from the water evidently allows a new force to come into full play4 ,we may call it what we like2 but cohesion1 from the ,latin cum1 together1 and hreo1 ,i stick or cleave1 appears to be the best and most rational term for this power which tends to make the atoms or particles of the same kind of matter move towards each other1 and to prevent them being separated or moved asunder4 ,that it is not merely hypothetical is shown by the following experiments4 ,if two pieces of lead are cast1 and the ends nicely scraped1 taking care not to touch the surfaces with the fingers1 they may by simple pressure be made to cohere1 and in that state of attraction may be lifted from the table by the ring which is usually inserted for convenience in the upper piece of lead2 they may be hung for some time from a proper support1 and the lower bit of lead will not break away from the upper one2 they may even be suspended1 as demonstrated by ,morveau1 in the vacuum of an air-pump1 to show that the cohesion is not mistaken for the pressure of the atmosphere1 and no separation occurs4 ,and when the union is broken by physical force1 it is surprising to notice the limited number of points1 like pin points1 where the cohesion has occurred2 whilst the weight of the lump of lead upheld against the force of gravitation reminds one forcibly of the attraction of a mass of soft iron by a powerful magnet1 and leads the philosophic inquirer to speculate on the principle of cohesion being only some masked form of magnetic or electrical attraction4 7,fig4 #ge47 ,illustration3 ,fig4 #ge4 ,a ,a4 ,two pieces of lead1 scraped clean at the surfaces ,b ,b4 ,c4 ,stand1 supporting the two pieces of lead attached to each other by cohesion4 ,page #fa ,a fine example of the same force is shown in the use of a pair of flat iron surfaces1 planed by the celebrated ,whitworth1 of ,manchester4 ,these surfaces are so true1 that when placed upon each other1 the upper one will freely rotate when pushed round1 in consequence of the thin film of air remaining between the surfaces1 which acts like a cushion1 and prevents the metallic cohesion4 ,when1 however1 the upper plate is slid over the lower one gradually1 so as to exclude the air1 then the two may be lifted together1 because cohesion has taken place4 7,fig4 #gf47 ,illustration3 ,fig4 #gf4 ,a4 ,whitworth's planes1 with film of air between them4 ,b4 ,film of air excluded when cohesion occurs4 ,a glass vessel is a good example of cohesion4 ,the materials of which it is composed have been soft and liquid when melted in the fire1 and on the removal of the excess of heat it has become hard and solid1 in consequence of the attractive force of cohesion binding the particles together2 in the absence of such a power1 of course1 the material would fall into the condition of dust1 and a mere shapeless heap of silicates of potash and lead would indicate the place where the moulded and coherent glass would otherwise stand4 ,a lump of lead1 six inches long by four broad1 and half an inch thick1 may be supported by dexterously taking off a thick shaving with a proper plane1 and after pressing an inch or more of the strip on the planed surface of the large lump of lead1 the cohesion is so powerful that the latter may be lifted from the table by the strip of metal4 ,the bullets projected from ,perkins' steam-gun1 at the rate of three hundred per minute1 are thrown with such violence1 that1 when received on a thick plate of lead backed up with sheet iron1 a cold welding takes place between the two surfaces of metal in the most perfect manner1 just as two soft pieces of the metal potassium may be squeezed and welded together4 ,the surfaces of an apple torn asunder will not readily cohere1 but if cut with a sharp knife1 cohesion easily occurs2 so with a wound produced by a jagged surface1 it is difficult to make the parts ,page #fb heal1 whereas some of the most desperate sabre-cuts have been healed1 the cohesion of the surfaces of cut flesh being very rapid2 hence1 if the top of a finger is cut off1 it may be replaced1 and will grow1 in consequence of the natural cohesion of the parts4 ,the art of plating copper with silver1 which is afterwards gilt1 and then drawn out into flattened wire for the manufacture of gold lace and epaulets1 usually termed bullion1 is another example of the wonderful cohesion of the particles of gold1 of which a single grain may be extended over the finest plate wire measuring #cde feet in length4 ,the process of making wax candles is a good illustration of the attraction of cohesion2 they are not generally cast in moulds1 as most persons suppose1 but are made by the successive applications of melted wax around the central plaited wick4 ,other examples of cohesion are shown by icicles1 and also stalagmites2 which latter are produced by the gradual dropping of water containing chalk 7carbonate of lime7 held in solution by the excess of carbonic acid gas2 the solvent gradually evaporates1 and leaves a series of calcareous films1 and these cohere in succession1 producing the most fantastic forms1 as shown in various remarkable caverns1 and especially in the cave of ,arta1 in the island of ,majorca4 ,in metallic substances the cohesion of the particles assumes an important bearing in the question of relative toughness and power of resisting a strain2 hence the term cohesion is modified into that of the property of tenacity4 ,the tenacity of the different metals is determined by ascertaining the weight required to break wires of the same length and gauge4 ,iron appears to possess the property of tenacity in the greatest1 and lead in the least degree4 7,fig4 #gg47 ,illustration3 ,fig4 #gg4 ,b4 ,pan supported by leaden wire broken by a weight which the iron wire at ,a easily supports4 ,page #fc ,the tenacity of iron is taken advantage of in the most scientific manner by the great engineers who have constructed the ,britannia ,tube1 and that eighth wonder of the world1 the ,leviathan1 or ,great ,eastern steam-ship4 ,in both of these sublime embodiments of the genius and industrial skill of ,great ,britain the advantage of the cellular principle is fully recognised4 ,the magnitude of this colossal ship is better realized when it is remembered that the ,great ,eastern is six times the size of the ,duke of ,wellington line-of-battle ship1 that her length is more than three times that of the height of the ,monument1 while in breadth it is equal to the width of ,pall ,mall1 and that a promenade round the deck will afford a walk of more than a quarter of a mile4 ,up to the water-mark the hull is constructed with an inner and outer shell1 two feet ten inches apart1 each of three-quarter-inch plate2 and between them1 at intervals of six feet1 run horizontal webs of iron plates1 which convert the whole into a series of continuous cells or iron boxes4 7,fig4 #gh47 ,illustration3 ,fig4 #gh4 ,transverse section of ,great ,eastern1 showing the cellular construction from keel to water-line1 ,a ,a4 ,this double ship is useful in various ways2 in the first place1 the danger arising from collision is diminished1 as it is supposed that the outer web only would be broken through or damaged2 so that the water would not then rush into the steam-ship1 but merely fill the space between the shells4 ,in the second place1 if there should be any difficulty in procuring ballast1 the space can be filled with #bejj tons of water1 or again pumped out1 according to the requirements of the vessel4 ,the strength of a continued cellular construction can be easily imagined1 and may be well illustrated by a thin sheet of common tin plate4 ,if the ends be rested on blocks of wood1 so as to lap over the wood about one inch1 they are easily displaced1 and the mimic bridge broken down from its ,page #fd supports by the addition to the centre of a few ounce weights2 whilst the same tin plate rolled up in the figure of a tube1 and again rested on the same blocks1 will now support many pounds weight without bending or breaking down4 7,fig4 #gi47 ,illustration3 ,fig4 #gi4 ,a4 ,flat tin plate1 breaking down with a few ounce weights4 ,b4 ,same tin plate rolled up supports a very heavy weight4 ,the deck of the ship is double or cellular1 after the plan of ,stephenson in the ,britannia ,tubular ,bridge1 and is #fib feet in length4 ,the tonnage register is #ah1bjj tons1 and #bb1ejj tons builder's measure2 the hull of the ,great ,eastern is considered to be of such enormous tenacity1 that1 if it were supported by massive blocks of stone six feet square1 placed at each end1 at stem and stern1 it would not deflect1 curve1 or bend down in the middle more than six inches even with all her machinery1 coals1 cargo1 and living freight4 ,in adducing remarkable instances of the adhesive power and tenacity of inorganic matter1 it may not be altogether out of place to allude to the strength and force of living matter1 or muscular power4 ,it is stated that ,dr4 ,george ,b4 ,winship1 of ,roxbury in ,america1 a young physician1 twenty-five years old1 and weighing #adc pounds1 is the strongest man alive2 in fact1 quite the ,samson of the nineteenth century4 ,he can raise a barrel of flour from the floor to his shoulders2 can raise himself with either little finger till his chin is half a foot above it2 can raise #bjj pounds with either little finger2 can put up a church bell of #ada pounds2 can lift with his hands #ibf pounds dead weight without the aid of straps or belts of any kind4 ,as compared with ,topham1 the ,cornish strong man1 who could raise #hjj pounds1 or the ,belgic one1 his power is greater2 and as the use of straps and belts increases the power of lifting by about four times1 it is stated that ,winship could lift at least #bejj pounds weight4 ,illustration3 ,fig4 #hj4 ,a4 ,ordinary glass water hammer4 ,b4 ,copper tube ditto1 showing exhausting syringe at ,d1 the height of the water at ,b1 and the end to be placed in the fire at ,c4 ,with these illustrations of cohesion we may return again to the abstract consideration of this power with reference to water1 in which we have noticed that the antagonist to this kind of attraction is the force or power termed caloric or heat4 ,the latter influence removes the frozen bands of winter and converts the ice to the next condition1 water4 ,in this state cohesion is almost concealed1 although there is just a slight ,page #fe excess to hold even the particles of water in a state of unity1 and this fact is beautifully illustrated by the formation of the brilliant diamond drops of dew on the surfaces of various leaves1 as also in the force and power exercised by great volumes of water1 which exert their mighty strength in the shape of breaker-waves1 dashing against rocks and lighthouses1 and making them tremble to their very base by the violence of the shock2 here there must be some unity of particles1 or the collective strength could not be exerted1 it would be like throwing a handful of sand against a window--a certain amount of noise is produced1 but the glass is not fractured2 whilst the same sand united by any glutinous material1 would break its way through1 and soon fracture the brittle glass4 ,it is so usual to see the particles of water easily separated1 that it becomes difficult to recognise the presence of cohesion2 but this bond of union is well illustrated in the experiment of the water hammer4 ,the little instrument is generally made of a glass tube with a bulb at one end2 in this bulb the water which it contains is boiled1 and as the steam issues from the other extremity1 drawn out to a capillary tube1 the opening is closed by fusion with the heat of a blowpipe flame4 ,as the water cools the steam condenses1 and a vacuum1 so far as air is concerned1 is produced2 if now the tube is suddenly inverted1 the whole of the water falls en masse1 collectively1 and striking against the bottom of the tube1 produces a metallic ring1 just as if a piece of wood or metal were contained within the tube4 ,if the end to which the water falls is not well cushioned by the palm of the hand1 the water hammers itself through and breaks away that part of the glass tube4 ,hence it is better to construct the water hammer of copper tube1 about three-quarters of an inch in diameter and three feet long2 at one end a female screw-piece is inserted1 into which a stop-cock is fitted2 when the tube is filled to the height of about six inches with water1 and shaken1 the air divides the descending volume of water1 and the ordinary splashing sound is heard2 there is no unity or cohesion of the parts2 if1 however1 the end of the copper tube is thrust into a fire and the water boiled so that steam issues from the cock1 which is then closed1 and the tube removed and cooled1 a smart blow is given1 and distinctly heard when the copper tube is rapidly inverted or shaken so as to cause the water to rise ,page #ff and fall4 ,the experiment may be rendered still more instructive by turning the cock and admitting the air1 which rushes in with a whizzing sound1 and on shaking the tube the metallic ring is no longer heard1 but it may be again restored by attaching a small air syringe or hand pump1 and removing the air by exhaustion4 7,fig4 #hj47 ,in the fluid condition water still possesses a surplus of cohesion over the antagonistic force of heat2 when1 however1 the latter is applied in excess1 then the quasi-struggle terminates2 the heat overpowers the cohesive attraction1 and converts the water into the most willing slave which has ever lent itself to the caprices of man--viz41 into steam--glorious1 useful steam3 and now the other end of the chain is reached1 where heat triumphs2 whilst in solids1 such as ice1 cohesion is the conqueror1 and the intermediate link is displayed in the fluid state of water4 ,if any fact could give an idea of the gigantic size of the ,great ,eastern1 it is the force of the steam which will be employed to move it at the rate of about eighteen miles per hour with a power estimated at the nominal rate of #bfjj horses1 but absolutely of at least #ab1jjj horses4 ,this steam power1 coupled with the fact that she has been enormously strengthened in her sharp1 powerful bows1 by laying down three complete iron decks forward1 extending from the bows backward for #abj feet1 will demonstrate that in case of war the ,great ,eastern may prove to be a powerful auxiliary to the ,government4 ,these decks will be occupied by the crew of #cjj or #djj men1 and with this large increase of strength forward1 the ,great ,eastern1 steaming full power1 could overtake and cut in two the largest wooden line-of-battle ship that ever floated4 ,should war unhappily spread to peaceful ,england1 and the enormous power of this vessel be realized1 her name would not inappropriately be changed from the ,great ,eastern to the ,great ,terror of the ocean4 ,the ,times very properly inquires1 ,what fleet could stand in the way of such a mass1 weighing some #cj1jjj tons1 and driven through the water by #ab1jjj horse-power1 at the rate of twenty-two or twenty-three miles per hour4 ,to produce the steam1 #bej tons of coal per diem will be required1 and great will be the honourable pride of the projectors when they see her fairly afloat1 and gliding through the ocean to the ,far ,west4 ,a good and striking experiment1 displaying the change from the liquid to the vapour state1 is shown by tying a piece of sheet caoutchouc over a tin vessel containing an ounce or two of water4 ,when this boils1 the india-rubber is distended1 and breaks with a loud noise2 or in another illustration1 by pouring some ether through a funnel carefully into a flask placed in a ring stand4 ,if flame is applied to the orifice1 no vapour issues that will ignite1 provided the neck of the flask has not been wetted with the ether4 ,when1 however1 the heat of a spirit-lamp is applied1 the ether soon boils1 and now on the application of a lighted taper1 a flame some feet in length is produced1 which is regulated by the spirit-lamp below1 and when this is removed1 the length of the flame diminishes immediately1 and is totally extinguished if the bottom of the flask is plunged into cold water2 the withdrawal of the heat restores the power of cohesion4 ,another illustration of the vast power of steam ,page #fg will be shortly displayed in the ,steam ,ram2 and1 ,supposing1 says the ,times1 the new steam ram to prove a successful design1 the finest specimens of modern men-of-war will be reduced by comparison to the helplessness of cock boats4 ,conceive a monstrous fabric floating in mid-channel1 fire proof and ball proof1 capable of hurling broadsides of #ajj shot to a distance of six miles2 or of clapping on steam at pleasure and running down everything on the surface of the sea with a momentum utterly irresistible4 ,this terrible engine of destruction is expected to be itself indestructible4 ,we are told that she may be riddled with shot 7supposing any shot could pierce her sides71 that she may have her stem and her stern cut to pieces1 and be reduced apparently to a shapeless wreck1 without losing her buoyancy or power4 ,supposing that she relies upon the shock of her impact instead of fighting her guns1 it is calculated that she would sink a line-of-battle ship in three minutes1 so that a squadron as large as our whole fleet now in commission would be destroyed in about one hour and a quarter4 ,,chapter ,,vii4 ,,adhesive ,,attraction4 ,the term cohesion must not be confounded with that of adhesion1 which refers to the clinging to or attraction of bodies of a dissimilar kind4 ,the late ,professor ,daniell defines cohesion to be an attraction of homogeneous 7,greek3 homos1 like1 and ,greek3 genos1 kind7 or similar particles2 adhesion to be an attraction subsisting between particles of a heterogeneous1 ,greek3 eteros1 different1 and ,greek3 genos1 kind4 ,there are numerous illustrations of adhesion1 such as mending china1 and the use of glue1 or paste1 in uniting different surfaces1 or mortar1 in building with bricks2 it is also well shown at the lecture table by means of a pair of scales1 one scale-pan of which being well cleaned with alkali at the bottom1 may then be rested on the surface of water contained in a plate2 the adhesion between the water and the metal is so perfect1 that many grain weights may be placed in the other pan before the adhesion is broken2 and after breakage1 if the pan be again placed on the water1 and a few grains removed from the other1 so as to adjust the two pans1 and make them nearly equal1 a drop of oil of turpentine being added1 instantly spreads itself over the water1 and breaking the adhesion between the latter and the metal1 the scale-pan is immediately and again broken away1 as the adhesion between the turpentine and the metal is not so great as that of water and metal4 ,the adhesion of air and water is well displayed in an apparatus recommended for ventilating mines1 in which a constant descending stream of water carries with it a quantity of air1 which being disengaged1 is then forced out of a proper orifice4 ,the same kind of adhesion between air and water is displayed in the ancient ,page #fh ,spanish ,catalan forge1 where the blast is supplied to the iron furnace on a similar principle1 only1 a natural cascade is taken advantage of instead of an artificial fall of water through a pipe4 ,the adhesion of air and water becomes of some value when a river flows through a large and crowded city1 because the water in its passage to and fro1 must necessarily drag with it1 a continuous column of air1 and assist in maintaining that constant agitation of the air which is desirable as a preventive to any accumulation of noxious air charged with foetid odours1 arising from mud banks or from other causes4 ,the fact of adhesion1 existing between water and air1 is readily shown1 by resting one end of a long glass tube1 of at least one inch diameter1 on a block of wood one foot high4 ,if water is allowed to flow down the tube1 so as to leave a sufficient space of air above it1 the adhesion between the two ancient elements becomes apparent1 directly a little smoke is produced1 near the top end of the glass tube resting on the block of wood4 ,the smoke1 which has a greater tendency to rise than to fall1 is dragged down the glass tube1 and accompanies the water as it flows from the higher to the lower level4 ,the same truth is also illustrated in horizontal troughs or tubes through which water is caused to flow4 ,the adhesion between air and glass is so great1 that it is absolutely necessary to boil the mercury in the tubes of the best barometers2 and if this is not carefully attended to1 the adhering air between the glass and mercury gradually ascends to1 and destroys1 the ,torricellian vacuum at the top of the barometer tube4 ,even after the mercury is boiled1 the air will creep up in course of years2 and in order to prevent its passage between the glass and quicksilver1 it has been recommended1 that a platinum ring should be welded on to the end of the glass tube1 because mercury has the power of wetting or enfilming the metal platinum1 and the two being in close contact1 would1 as it were1 shut the only door by which the air could enter the barometer tube4 ,illustration3 ,fig4 #ha4 ,model of the apparatus for drawing down air4 ,a1 cistern of water1 supplied by ball-cock1 and kept at one level1 so that the water just runs down the sides of the tube1 and draws down the air in the centre1 ,b ,c4 ,the vessel to which the air and water are conveyed by a gutta-percha tube1 ,t4 ,there is another ball-cock to permit the waste water to run away when it reaches a certain level2 the end of the pipe always dips some inches into this water1 whilst the air escapes from the jet1 ,d4 ,page #fi ,,chapter ,,viii4 ,,capillary ,,attraction4 ,this kind of attraction is termed capillary1 in consequence of tubes1 of a calibre1 or bore1 as fine as hair1 attracting and retaining fluids4 ,if water is poured into a glass1 the surface is not level1 but cupped at the edges1 where the solid glass exerts its adhesive attraction for the liquid1 and draws it from the level4 ,if the glass be reduced to a very narrow tube1 having a hair-like bore1 the attraction is so great that the water is retained in the tube1 contrary to the force of gravitation4 ,two pieces of flat glass placed close together1 and then opened like a book1 draw up water between them1 on the same principle4 ,a mass of salt put on a plate containing a little water coloured with indigo displays this kind of attraction most perfectly1 and the water is quickly drawn up1 as shown by the blue colour on the salt4 ,a little solution of the ammonio-sulphate of copper imparts a finer and more distinct blue colour to the salt4 ,a piece of dry ,honduras mahogany one inch square1 placed in a saucer containing a little turpentine1 is soon found to be wet with the oil at the top1 which may then be set on fire4 ,almost every kind of wood possesses capillary tubes1 and will float1 on account of these minute vessels being filled with air2 if1 however1 the air is withdrawn1 then the wood sinks1 and by boiling a ball made of beech wood in water1 and then placing it under the vacuum of an air pump in other cold water1 it becomes so saturated with water that it will no longer float4 ,a remarkable instance of the same kind is mentioned by ,scoresby1 in which a boat was pulled down by a whale to a great depth in the ocean1 and after coming to the surface it was found that the wood would neither swim nor burn1 the capillary pores being entirely filled with salt water4 ,a piece of ebony sinks in water on account of its density1 closeness1 and freedom from air4 ,a gauge made of a piece of oak1 with a hole bored in it of one inch diameter1 accurately receives a dry plug of willow wood which will not enter the orifice after it is wetted4 ,millstones are split by inserting wedges of dry hard wood1 which are afterwards wetted and swelled1 and burst the stone asunder4 ,one of the most curious instances of capillary attraction is shown in the currying of leather1 a process which is intended to impart a softness and suppleness to the skin1 in order that it may be rendered fit for the manufacture of boots1 harness1 machine bands1 c4 ,the object of the currier is to fill the pores of the leather with oil1 and as this cannot be done by merely smearing the surface1 he prepares the way for the oil by wetting the leather thoroughly with water1 and whilst the skin is damp1 oil is rubbed on1 and it is then exposed to the air2 the water evaporates at ordinary temperatures1 but oil does not2 the consequence is that the ,page #gj pores of the leather give up the water1 which disappears in evaporation1 and the oil by capillary attraction is then drawn into the body of the leather1 the oil in fact takes the place vacated by the water1 and renders the material very supple1 and to a considerable extent waterproof4 ,in paper making1 the pores of this material1 unless filled up or sized1 cause the ink to blot or spread by capillary attraction4 ,the porosity of soils is one of the great desideratums of the skilful agriculturist1 and drainage is intended to remove the excess of water which would fill the pores of the earth1 to the exclusion of the more valuable dews and rains conveying nutritious matter derived from manures and the atmosphere4 ,a cane is an assemblage of small tubes1 and if a piece of about six inches in length 7cut off1 of course1 from the joints7 be placed in a bottle of turpentine1 the oil is drawn up and may be burnt at the top2 it is on this principle that indestructible wicks of asbestos1 and wire gauze rolled round a centre core1 are used in spirit lamps4 ,oil1 wax1 and tallow1 all rise by capillary attraction in the wicks to the flame1 where they are boiled1 converted into gas1 and burnt4 ,illustration3 ,fig4 #hb4 ,geber's filter4 ,a4 ,the solution of acetate of lead4 ,b4 ,the dilute sulphuric acid4 ,c4 ,the clear liquid1 separated from the sulphate of lead in ,b4 ,illustration3 ,fig4 #hc4 ,prawn syphon4 ,the capillary attraction of skeins of cotton for water was known and appreciated by the old alchemists2 and ,geber1 one of the most ancient of these pioneers of science1 and who lived about the seventh century1 describes a filter by which the liquid is separated from the solid4 ,this experiment is well displayed by putting a solution of acetate of lead into a glass1 which is placed on the highest block of a series of three1 arranged as steps4 ,into this glass is placed the short end of a skein ,page #ga of lamp cotton1 previously wetted with distilled water2 the long end dips into another glass below1 containing dilute sulphuric acid1 and as the solution of lead passes into it1 a solid white precipitate of sulphate of lead is formed2 then another skein of wetted cotton is placed in this glass1 the long end of which passes into the last glass1 so that the clear liquid is separated and the solid left behind4 7,fig4 #hb47 ,in this filter the lamp cotton acts as a syphon through the capillary pores which it forms4 ,on the same principle1 a prawn may be washed in the most elegant manner 7as first shown by the late ,duke of ,sussex71 by placing the tail1 after pulling off the fan part1 in a tumbler of water1 and allowing the head to hang over1 when the water is drawn up by capillary attraction1 and continues to run through the head4 7,fig4 #hc47 ,the threads of which linen1 cotton1 and woollen cloths are made are small cords1 and the shrinkage of such textile fabrics1 is well known and usually inquired about1 when a purchase is made2 here again capillary attraction is exerted1 and the fabric contracts in the two directions of the warp and woof threads2 thus1 twenty-seven yards of common ,irish linen will permanently shrink to about twenty-six yards in cold water4 ,in these cases the water is attracted into the fibres of the textile material1 and causing them to swell1 must necessarily shorten their length1 just as a dry rope strained between two walls for the purpose of supporting clothes1 has been known to draw the hooks after being suddenly wetted and shortened by a shower of rain4 ,in order to tighten a bandage1 it is only necessary to wind the dry linen round the limbs as close as possible1 and then wet it with water1 when the necessary shrinkage takes place4 ,if a piece of dry cotton cloth is tied over one end of a lamp glass1 the other may be thrust into1 or removed from the basin of water very easily1 but when the cotton is wetted1 the fibres contract and prevent air from entering1 so that the glass retains water just as if it were an ordinary gas jar closed with a glass stopper4 ,illustration3 ,fig4 #hd4 ,a4 ,basin of water4 ,b4 ,cylinder of wire gauze closed at both ends with gauze4 ,when full of water it may be lifted from the basin by the handle1 ,c4 ,a ,spanish proverb1 expressing contempt1 says1 go to the well with a sieve1 but even this seeming impossibility is surmounted by using a cylinder of wire gauze1 which may be filled with water1 and by means of the capillary attraction between the meshes of the copper-wire gauze and the water1 the whole is retained1 and may be carefully lifted from a basin of water2 the experiment only succeeds when the air is completely driven out of the interstices of the gauze1 and the little cylinder completely filled with water2 this may be done ,page #gb by repeatedly sinking and drawing out the cylinder1 or still more effectually1 by first wetting it with alcohol and then dipping the cylinder in water4 ,a balloon1 made of cotton cloth1 cannot be inflated by means of a pair of bellows1 but if the balloon is wetted with water1 then it may be swelled out with air just as if it had been made of some air-tight material2 hence the principle of varnishing silk or filling the pores with boiled oil1 when it is required in the manufacture of balloons4 ,biscuit ware1 porous tubes for voltaic batteries1 alcarrazas1 or water coolers1 are all examples of the same principle4 ,whilst speaking most favourably of the benevolent labours of many gentlemen 7beginning with ,mr4 ,gurney7 who have erected ,drinking ,fountains in ,london's dusty atmosphere and crowded streets1 it must not be forgotten that pious ,mohammedans have1 in bygone times1 already set us the example in this respect2 and in the palmy days of many of the ,moorish cities1 the thirsty citizen could always be refreshed by a draught of cool water from the porous bottles provided and endowed by charitable ,mussulmans1 and placed in the public streets4 ,illustration3 ,fig4 #he4 ,moorish niche and porous earthenware bottle1 containing water4 ,page #gc ,,chapter ,,ix4 ,,crystallization4 ,illustration3 ,fig4 #hf4 ,crystals of snow4 ,it has been already stated that the force of cohesion binds the similar particles of substances together1 whether they be amorphous or shapeless1 crystalline or of a regular symmetrical and mathematical figure4 ,the term crystal was originally applied by the ancients to silica in the form of what is usually termed rock crystal1 or ,brazilian pebble2 and they supposed it to be water which had been solidified by a remarkable intensity of cold1 and could not be thawed by any ordinary or summer heat4 ,indeed1 this idea of the ancients has been embodied 7to a certain extent7 in the shape of artificial ice made by crystallizing large quantities of sulphate of soda1 which was made as flat as possible1 and upon ,page #gd which skaters were invited to describe the figure of eight1 at the usual admittance fee1 representing twelve pence4 ,a crystal is now defined to be an inorganic body1 which1 by the operation of affinity1 has assumed the form of a regular solid terminated by a certain number of planes or smooth surfaces4 ,thousands of minerals are discovered in the crystallized state--such as cubes of iron pyrites 7sulphuret of iron7 and of fluor spar 7fluoride of calcium71 whilst numerous saline bodies called salts are sold only in the form of crystals4 ,of these salts we have excellent examples in ,epsom salts 7sulphate of magnesia71 nitre 7nitrate of potash71 alum 7sulphate of alumina71 and potash2 the term salt being applied specially to all substances composed of an acid and a base1 as also to other combinations of elements which may or may not take a crystalline form4 ,thus1 nitre is composed of nitric acid and potash2 the first1 even when much diluted1 rapidly changes paper1 dipped in tincture of litmus and stained blue1 to a red colour1 whilst potash shows its alkaline nature1 by changing paper1 stained yellow with tincture of turmeric1 to a reddish-brown4 ,the latter paper is restored to its original yellow by dipping it into the dilute nitric acid1 whilst the litmus paper regains its delicate blue colour by being passed into the alkaline solution4 ,an acid and an alkali combine and form a neutral salt1 such as nitre1 which has no action whatever on litmus or turmeric2 whilst the element iodine1 which is not an acid1 unites with the metallic element potassium1 and therefore not an alkali1 and forms a salt that crystallizes in cubes called iodide of potassium4 ,again1 cane sugar1 which is composed of charcoal1 oxygen1 and hydrogen1 crystallizes in hard transparent four-sided and irregular six-sided prisms1 but is not called a salt4 ,silica or sand is found crystallized most perfectly in nature in six-sided pyramids1 but is not a salt2 it is an acid termed silicic-acid4 ,sand has no acid taste1 because it is insoluble in water1 but when melted in a crucible with an alkali1 such as potash1 it forms a salt called silicate of potash4 ,magnesia1 from being insoluble1 or nearly so1 in water1 is all but tasteless1 and has barely any alkaline reaction1 yet it is a very strong alkaline base2 #bj4g parts of it neutralize as much sulphuric acid as #dg of potash4 ,a salt is not always a crystallizable substance1 and vice vers4 ,the progress of our chemical knowledge has therefore demanded a wider extension and application of the term salt1 and it is not now confined merely to a combination of an acid and an alkali1 but is conferred even on compounds consisting only of sulphur and a metal1 which are termed sulphur salts4 ,so also in combinations of chlorine1 iodine1 bromine1 and fluorine1 with metallic bodies1 neither of which are acid or alkaline1 the term haloid salts has been applied by ,berzelius1 from the ,greek 7,greek3 als1 sea salt1 and ,greek3 eidos form71 because they are analogous in constitution to sea salt2 and the mention of sea salt again reminds us of the wide signification of the term salt1 originally confined to this substance1 but now extended into four great orders1 as defined by ,turner3-- ,,order ,i4 ,the oxy-salts4--,this order includes no salt the acid or base of which is not an oxidised body 7ex41 nitrate of potash74 ,page #ge ,,order ,,ii4 ,the hydro-salts4--,this order includes no salt the acid or base of which does not contain hydrogen 7ex41 chloride of ammonium74 ,,order ,,iii4 ,the sulphur salts4--,this order includes no salt the electro-positive or negative ingredient of which is not a sulphuret 7ex41 hydrosulphuret of potassium74 ,,order ,,iv4 ,the haloid salts4--,this order includes no salt the electro-positive or negative ingredient of which is not haloidal4 7,exs41 iodide of potassium and sea salt74 ,to fix the idea of salt still better in the youthful mind1 it should be remembered that alabaster1 of which works of art are constructed1 or marble1 or lime-stone1 or chalk1 are all salts1 because they consist of an acid and a base4 ,in order to cause a substance to crystallize it is first necessary to endow the particles with freedom of motion4 ,there are many methods of doing this chemically or by the application of heat1 but we cannot by any mechanical process of concentration1 compression1 or division1 persuade a substance to crystallize1 unless perhaps we except that remarkable change in wrought or fibrous iron into crystalline or brittle iron1 by constant vibration1 as in the axles of a carriage1 or by attaching a piece of fibrous iron to a tilt hammer4 ,if we powder some alum crystals they will not again assume their crystalline form2 if brought in contact there is no freedom of motion4 ,it is like placing some globules of mercury on a plate4 ,they have no power to create motion2 their inertia keeps them separated by certain distances1 and they do not coalesce2 but incline the plate1 give them motion1 and bring them in contact1 they soon unite and form one globule4 ,the particles of alum are not in close contact1 and they have no freedom of motion unless they are dissolved in water1 when they become invisible2 the water by its chemical power destroys the mechanical aggregation of the solid alum far beyond any operation of levigation4 ,the solid alum has become liquid1 like water2 the particles are now free to move without let or hindrance from friction4 ,a solution1 7from the ,latin solvo1 to loosen7 is obtained4 ,the alum must indeed be reduced to minute particles1 as they are alike invisible to the eye whether assisted by the microscope or not4 ,no repose will cause the alum to separate2 the solvent power of the water opposes gravitation2 every part of the solution is equally impregnated with alum1 and the particles are diffused at equal distances through the water2 the heavy alum is actually drawn up against gravity by the water4 ,how1 then1 is the alum to be brought back again to the solid state8 ,the answer is simple enough4 ,by evaporating away the excess of water1 either by the application of heat or by long exposure to the atmosphere in a very shallow vessel1 the minute atoms of the alum are brought closer together1 and crystallization takes place4 ,the assumption of the solid state is indicated by the formation of a thin film 7called a pellicle7 of crystals1 and is further and still more satisfactorily proved by taking out a drop of the solution and placing it on a bit of glass1 which rapidly becomes filled with crystals if the evaporation has been carried sufficiently far 7,fig4 #hg74 ,page #gf ,after evaporating away sufficient water1 the dish is placed on one side and allowed to cool1 when crystals of the utmost regularity of form are produced1 and1 denoted by a geometrical term1 are called octohedral or eight-sided crystals1 when in the utmost state of perfection 7,fig4 #hh74 ,illustration3 ,fig4 #hg4 ,r ,r4 ,ring-stand4 ,s ,s4 ,spirit-lamps4 ,a4 ,flask containing boiling solution of alum4--,solution4 ,b4 ,funnel1 with a bit of lamp-cotton stuffed in the bottom4--,filtration4 ,c4 ,evaporating dish4--,evaporation4 ,d4 ,drop on glass4--,crystallization4 ,illustration3 ,fig4 #hh4 ,the science of crystallography is too elaborate to be discussed at length in a work of this kind2 the various terms connected with crystals will therefore only be explained1 and experiments given in illustration of the formation of various crystals4 ,when the apices--i4e41 the tips or points of crystals--are cut off1 they are said to be truncated2 and the same change occurs on the edges of numerous crystals4 ,if some of the salt called chloride of calcium in the dry and amorphous state is exposed to the air1 it soon absorbs water1 or what is termed deliquesces3 the same thing occurs with the crystals of carbonate of potash1 and if four ounces are weighed out in an evaporating dish1 and then exposed for about half an hour to the air1 a very perceptible increase in weight is observed by the assistance of the scales and grain weights4 ,deliquescence is a term from the ,latin deliqueo1 to melt1 and is in fact a gradual melting1 caused by the absorption of water from the atmosphere4 ,the reverse of this is illustrated with various crystals1 such as ,glauber's salt 7sulphate of soda71 or common washing soda 7carbonate of soda72 if a fine clear crystal is taken out of the solution1 called the mother liquor1 in which it has been crystallized1 wiped dry1 and placed under a glass shade1 this salt may remain for a long period ,page #gg without change1 but if it receive one scratch from a pin1 the door is opened apparently for the escape of the water which it contains1 chemically united with the salt1 and called water of crystallization2 the white crystal gradually swells out1 the little quasi sore from the pin-scratch spreads over the whole1 which becomes opaque1 and crumbling down falls into a shapeless mass of white dust2 this change is called efflorescence1 from effloresco1 to blow as a flower--caused by the abstraction from them of chemically-combined water by the atmosphere4 ,with reference to the preservation of crystals1 ,professor ,griffiths recommends them to be oiled and wiped1 and placed under a glass shade1 if of a deliquescent nature2 or if efflorescent1 they are perfectly preserved by placing them under a glass shade with a little water in a cup to keep the air charged with moisture and prevent any drying up of the crystal4 ,deliquescent crystals may be preserved by placing them1 when dry1 in naphtha1 or any liquor in which they are perfectly insoluble4 ,some salts1 like ,glauber's salts1 contain so much water of crystallization that when subjected to heat they melt and dissolve in it1 and this liquefaction of the solid crystal is called watery fusion4 ,other salts1 such as bay salt1 chlorate of potash1 c41 when heated1 fly to pieces1 with a sharp crackling noise1 which is due sometimes1 to the unequal expansion of the crystalline surface1 or the sudden conversion of the water 7retained in the crystal by capillary attraction7 into steam2 thus nitre behaves in this manner1 and frequently retains water in capillary fissures1 although it is an anhydrous salt1 or salt perfectly free from combined water4 ,the crackling sound is called decrepitation1 and is well illustrated by throwing a handful of bay salt on a clear fire2 but this property is destroyed by powdering the crystals4 ,many substances when melted and slowly cooled concrete into the most perfect crystals2 in these cases heat alone1 the antagonist to cohesion1 is the solvent power4 ,thus1 if bismuth be melted in a crucible1 and when cooling1 and just as the pellicle 7from pellis1 a skin or crust7 is forming on the surface1 if two small holes are instantly made by a rod of iron and the liquid metal poured out from the inside 7one of the holes being the entrance for the air1 the other the exit for the metal72 on carefully breaking the crucible1 the bismuth is found to be crystallized in the most lovely cubes4 ,sulphur1 again1 may be crystallized in prismatic crystals by pursuing a similar plan2 and the great blocks of spermaceti exhibited by wax chandlers in their windows1 are crystallized in the interior and prepared on the same principle4 ,there are other modes of conferring the crystalline state upon substances--viz41 by elevating them into a state of vapour by the process called sublimation 7from sublimis1 high or exalted71 the lifting up and condensation of the vapour in the upper part of a vessel2 a process perfectly distinct from that of distillation1 which means to separate drop by drop4 ,both of these processes are very ancient1 and were invented by the ,arabian alchemists long antecedent to the seventh century4 ,examples of sublimation are shown by heating iodine1 and especially ,page #gh benzoic acid2 with the latter1 a very elegant imitation of snow is produced1 by receiving the vapour1 on some sprigs of holly or other evergreen1 or imitation paper snowdrops and crocuses1 placed in a tasteful manner under a glass vessel4 ,the benzoic acid should first be sublimed over the sprigs or artificial flowers in a gas jar1 which may be removed when the whole is cold1 and a clear glass shade substituted for it4 7,fig4 #hi47 ,all electro deposits on metals are more or less crystalline2 and copper or silver may be deposited in a crystalline form by placing a scraped stick of phosphorus in a solution of sulphate of copper or of nitrate of silver4 ,the phosphorus takes away the oxygen from the metal1 or deoxidizes the solution1 and the copper or silver reappears in the metallic form4 ,the surface of the phosphorus must not be scraped in the air1 but under water1 when the operation is perfectly safe4 ,a singular and almost instantaneous crystallization can be produced by saturating boiling water with ,glauber's salt1 of which one ounce and a half of water will usually dissolve about two ounces2 having done this1 pour the solution1 whilst boiling hot1 into clean oil flasks1 or vials of any kind1 previously warmed in the oven1 and immediately cork them1 or tie strips of wetted bladder1 over the orifices of the flasks or vials1 or pour into the neck a small quantity of olive oil1 or close the neck with a cork through which a thermometer tube has been passed4 ,when cold1 no crystallization occurs until atmospheric air is admitted2 and it was formerly believed that the pressure of the air effected this object1 until some one thought of the oil1 and now the theory is modified1 and crystallization is supposed to occur in consequence of the water dissolving some air which causes the deposit of a minute crystal1 and this being the turning point1 the whole becomes solid4 ,however the fact may be explained1 it is certain that when the liquid refuses to crystallize on the admission of air1 the solidification occurs directly a minute crystal of sulphate of soda1 or ,glauber's salt1 is dropped into the vessel4 ,when the crystallization is accomplished1 the whole mass is usually so completely solidified1 that on inverting the vessel1 not a drop of liquid falls out4 ,illustration3 ,fig4 #hi4 ,a4 ,gas-jar1 with stopper open at first1 to be shut when the lamp is withdrawn4 ,b4 ,wooden stand1 with hole to carry the cup ,c1 containing the benzoic acid1 heated below by the spirit-lamp1 ,s4 ,f4 ,flowers or sprigs arranged on pieces of rock or mineral4 ,page #gi ,it may be observed that the same mass of salt will answer any number of times the same purpose4 ,all that is necessary to be done1 is to place the vial or flask1 in a saucepan of warm water1 and gradually raise it to the boiling point till the salt is completely liquefied1 when the vessel must be corked and secured from the air as before4 ,when the solidification is produced much heat is generated1 which is rendered apparent by means of a thermometer1 or by the insertion of a copper wire into the pasty mass of crystal in the flask1 and then touching an extremely thin shaving or cutting of phosphorus1 dried and placed on cotton wool4 ,solidification in all cases produces heat4 ,liquefaction produces cold4 ,in ,masters's freezing apparatus certain measured quantities of crystallized sal-ammoniac1 nitre1 and nitrate of ammonia1 are placed in a metallic cylinder1 surrounded with a small quantity of spring water contained in an outer vessel4 ,directly the crystals are liquefied by the addition of water1 intense cold is produced1 which freezes the water and forms an exact cast of the inner cylinder in ice1 and this may afterwards be removed1 by pouring away the liquefied salts1 and filling the inner cylinder1 with water of the same temperature as the air1 which rapidly thaws the surrounding ice1 and allows it to slip off into any convenient vessel ready to receive it4 7,fig4 #ij47 ,illustration3 ,fig4 #ij4 ,a4 ,the inner cylinder which contains the freezing mixture4 ,b ,b4 ,the outer one containing spring water4 ,c ,c4 ,the ice slipping away from the inner cylinder4 ,for an ingenious method of obtaining large and perfect crystals of almost any size1 experimentalists are indebted to ,le ,blanc4 ,his method consists in first procuring small and perfect crystals--say1 octohedra of alum--and then placing them in a broad flat-bottomed pan1 he pours over the crystals a quantity of saturated solution of alum1 obtained by evaporating a solution of alum until a drop taken out crystallizes on cooling4 ,the positions of the crystals are altered at least once a day with a glass rod1 so that all the faces may be alternately exposed to the action of the solution1 for the side on which the crystal rests1 or is in contact with the vessel1 never receives any increment4 ,the crystals will thus gradually grow or increase in size1 and when they have done so for some time1 the best and most symmetrical1 may be removed and placed separately1 in vessels containing some of the same saturated ,page #hj solution of alum1 and being constantly turned they may be obtained of almost any size desired4 ,unless the crystals are removed to fresh solutions1 a reaction takes place1 in consequence of the exhaustion of the alum from the water1 and the crystal is attacked and dissolved4 ,this action is first perceptible on the edges and angles of the crystal2 they become blunted and gradually lose their shape altogether4 ,by this method crystals may be made to grow in length or breadth--the former when they are placed upon their sides1 the latter if they be made to stand upon their bases4 ,on ,le ,blanc's principle1 beautiful crystal baskets are made with alum1 sulphate of copper1 and bichromate of potash4 ,the baskets are usually made of covered copper wire1 and when the salts crystallize on them as a nucleus or centre1 they are constantly removed to fresh solutions1 so that the whole is completely covered1 and red1 white1 and blue sparkling crystal baskets formed4 ,they will retain their brilliancy for any time1 by placing them under a glass shade1 with a cup containing a little water4 ,the sketch below affords an excellent illustration of some of ,nature's remarkable concretions in the peculiar columnar structure of basalt4 ,illustration3 ,fig4 #ia4 ,the ,giant's ,causeway4 ,page #ha ,,chapter ,x4 ,,chemistry4 ,illustration3 ,fig4 #ib4 ,alchemists at work4 ,there is hardly any kind of knowledge which has been so slowly acquired as that of chemistry1 and perhaps no other science has offered such fascinating rewards to the labour of its votaries as the philosopher's stone1 which was to produce an unfailing supply of gold2 or the elixir of life1 that was to give the discoverer of the gold-making art the time1 the prolonged life1 in which he might spend and enjoy it4 ,hundreds of years ago ,egypt was the great depository of all learning1 art1 and science1 and it was to this ancient country that the most celebrated sages of antiquity travelled4 ,hermes1 or ,mercurius ,trismegistus1 the favourite minister of the ,egyptian king ,osiris1 has been celebrated as the inventor of the art of alchemy1 and the first treatise upon it has been attributed to ,zosymus1 of ,chemnis or ,panopolis4 ,the ,moors who conquered ,spain were remarkable ,page #hb for their learning1 and the taste and elegance with which they designed and carried out a new style of architecture1 with its lovely ,arabesque ornamentation4 ,they were likewise great followers of the art of alchemy1 when they ceased to be conquerors1 and became more reconciled to the arts of peace4 ,strange that such a people1 thirsting as they did in after years for all kinds of knowledge1 should have destroyed1 in the persons of their ancestors1 the most numerous collection of books that the world had ever seen3 the magnificent library of ,alexandria1 collected by the ,ptolemies with great diligence and at an enormous expense1 was burned by the orders of ,caliph ,omar2 whilst it is stated that the alchemical works had been previously destroyed by ,diocletian in the fourth century1 lest the ,egyptians should acquire by such means sufficient wealth to withstand the ,roman power1 for gold was then1 as it is now1 the sinews of war4 ,eastern historians relate the trouble and expense incurred by the succeeding ,caliphs1 who1 resigning the ,saracenic barbarism of their ancestors1 were glad to collect from all parts the books which were to furnish forth a princely library at ,bagdad4 ,how the learned scholar sighs when he reads of seven hundred thousand books being consigned to the ignominious office of heating forty thousand baths in the capital of ,egypt1 and of the magnificent ,alexandrian ,library1 a mental fuel for the lamp of learning in all ages1 consumed in bath furnaces1 and affording six months' fuel for that purpose4 ,the ,arabians1 however1 made amends for these barbarous deeds in succeeding centuries1 and when all ,europe was laid waste under the iron rule of the ,goths1 they became the protectors of philosophy and the promoters of its pursuits2 and thus we come to the seventh century1 in which ,geber1 an ,arabian prince lived1 and is stated to be the earliest of the true alchemists whose name has reached posterity4 ,without attempting to fill up the alchemical history of the intervening centuries1 we leap forward six hundred years1 and now find ourselves in imagination in ,england1 with the learned friar1 ,roger ,bacon1 a native of ,somersetshire1 who lived about the middle of the thirteenth century2 and although the continual study of alchemy had not yet produced the stone1 it bore fruit in other discoveries1 and ,roger ,bacon is said1 with great appearance of truth1 to have discovered gunpowder1 for he says in one of his works3--,from saltpetre and other ingredients we are able to form a fire which will burn to any distance2 and again alluding to its effects1 a small portion of matter1 about the size of the thumb1 properly disposed1 will make a tremendous sound and coruscation1 by which cities and armies might be destroyed4 ,the exaggerated style seems to have been a favourite one with all philosophers1 from the time of ,roger ,bacon to that of ,muschenbroek of the ,university of ,leyden1 who accidentally discovered the ,leyden jar in the year #agdf1 and receiving the first shock1 from a vial containing a little water1 into which a cork and nail had been fitted1 states that he felt himself struck in his arms1 shoulders1 and breast1 so that he lost his breath1 and was two days before he recovered from the effects of the blow and the terror2 ,page #hc adding1 that he would not take a second shock for the kingdom of ,france4 ,disregarding the numerous alchemical events occurring from the time of ,roger ,bacon1 we again advance four hundred years--viz41 to the year #affb1 when1 on the #aeth of ,july1 ,king ,charles ,,ii4 granted a royal charter to the ,philosophical ,society of ,oxford1 who had removed to ,london1 under the name of the ,royal ,society of ,london for ,promoting ,natural ,knowledge1 and in the year #affe was published the first number of the ,philosophical ,transactions2 this work contains the successive discoveries of ,mayow1 ,hales1 ,black1 ,leslie1 ,cavendish1 ,lavoisier1 ,priestley1 ,davy1 ,faraday2 and since the year #agfb has been regularly published at the rate of one volume per annum4 ,with this preface proceed we now to discuss some of the varied phenomena of chemical attraction1 or what is more correctly termed ,,chemical ,,affinity4 ,the above title refers to an endless series of changes brought about by chemical combinations1 all of which can be reduced to certain fixed laws1 and admit of a simple classification and arrangement4 ,a mechanical aggregation1 however well arranged1 can be always distinguished from a chemical one4 ,thus1 a grain of gunpowder consists of nitre1 which can be washed away with boiling water1 of sulphur1 which can be sublimed and made to pass away as vapour1 of charcoal1 which remains behind after the previous processes are complete2 this mixture has been perfected by a careful proportion of the respective ingredients1 it has been wetted1 and ground1 and pressed1 granulated1 and finally dried2 all these mechanical processes have been so well carried out that each grain1 if analysed1 would be similar to the other2 and yet it is1 after all1 only a mechanical aggregation1 because the sulphur1 the charcoal1 and the nitre are unchanged4 ,a grain of gunpowder moistened1 crushed1 and examined by a high microscopic power1 would indicate the yellow particles of sulphur1 the black parts of charcoal1 whilst the water filtered from the grain of powder and dried1 would show the nitre by the form of the crystal4 ,on the other hand1 if some nitre is fused at a dull red heat in a little crucible1 and two or three grains of sulphur are added1 they are rapidly oxidized1 and combine with the potash1 forming sulphate of potash2 and after this change a few grains of charcoal may be added in a similar manner1 when they burn brightly1 and are oxidized and converted into carbonic acid1 which also unites in like manner with the potash1 forming carbonate of potash2 so that when the fused nitre is cooled and a few particles examined by the microscope1 the charcoal and sulphur are no longer distinguishable1 they have undergone a chemical combination with portions of the nitre1 and have produced two new salts1 perfectly different in taste1 gravity1 and appearance from the original substances employed to produce them4 ,hence chemical combination is defined to be that property which is possessed by one or more substances1 of uniting together and producing a third or other body perfectly different ,page #hd in its nature from either of the two or more generating the new compound4 ,to return to our first experiment with the gunpowder3 take sulphur1 place some in an iron ladle1 heat it over a gas flame till it catches fire1 then ascend a ladder1 and pour it gently1 from the greatest height you can reach1 into a pail of warm water3 if this experiment is performed in a darkened room a magnificent and continuous stream of fire is obtained1 of a blue colour1 without a single break in its whole length1 provided the ladle is gradually inclined and emptied4 ,the substance that drops into the warm water is no longer yellow and hard1 but is red1 soft1 and plastic2 it is still sulphur1 though it has taken a new form1 because that element is dimorphous 7,greek3 dis twice1 and ,greek3 morph a form71 and1 ,proteus-like1 can assume two forms4 ,take another ladle1 and melt some nitre in it at a dull red heat1 then add a small quantity of sulphur1 which will burn as before2 and now1 after waiting a few minutes1 repeat the same experiment by pouring the liquid from the steps through the air into water2 observe it no longer flames1 and the substance received into the water is not red and soft and plastic1 but is white1 or nearly so1 and rapidly dissolves away in the water4 ,the sulphur has united with the oxygen of the nitre and formed sulphuric acid1 which combines with the potash and forms sulphate of potash2 here1 then1 oxygen1 sulphur1 and potassium1 have united and formed a salt in which the separate properties of the three bodies have completely disappeared2 to prove this1 it is only necessary to dissolve the sulphate of potash in water1 and after filtering the solution1 or allowing it to settle1 till it becomes quite clear and bright1 some solution of baryta may now be added1 when a white precipitate is thrown down1 consisting of sulphate of baryta1 which is insoluble in nitric or other strong acids4 ,the behaviour of a solution of sulphate of potash with a nitrate of baryta may now be contrasted with that of the elements it contains2 on the addition of sulphur to a solution of nitrate of baryta no change whatever takes place1 because the sulphur is perfectly insoluble4 ,if a stream of oxygen gas is passed from a bladder and jet through the same test1 no effect is produced2 the nitrate of baryta has already acquired its full proportion of oxygen1 and no further addition has any power to change its nature2 finally1 if a bit of the metal potassium is placed in the solution of nitrate of baryta it does not sink1 being lighter than water1 and it takes fire2 but this is not in any way connected with the presence of the test1 as the same thing will happen if another bit of the metal is placed in water--it is the oxygen of the latter which unites rapidly with the potassium1 and causes it to become so hot that the hydrogen1 escaping around the little red-hot globules1 takes fire2 moreover1 the fact of the combustion of the potassium under such circumstances is another striking proof of the opposite qualities of the three elements--sulphur1 oxygen1 and potassium--as compared with the three chemically combined and forming sulphate of potash4 ,the same kind of experiment may be repeated with charcoal2 if some powdered charcoal is made red-hot1 and then puffed into the air with a blowing machine1 numbers of sparks are produced1 and the ,page #he charcoal burns away and forms carbonic acid gas1 a little ash being left behind2 but if some more nitre be heated in a ladle1 and charcoal added1 a brilliant deflagration 7deflagro1 to burn7 occurs1 and the charcoal1 instead of passing away in the air as carbonic acid1 is now retained in the same shape1 but firmly and chemically united with the potash of the nitre1 forming carbonate of potash1 or pearl-ash1 which is not black and insoluble in water and acids like charcoal1 but is white1 and not only soluble in water1 but is most rapidly attacked by acids with effervescence1 and the carbon escapes in the form of carbonic acid gas4 ,thus we have traced out the distinction between mechanical aggregation and chemical affinity1 taking for an example the difference between gunpowder as a whole 7in which the ingredients are so nicely balanced that it is almost a chemical combination71 and its constituents1 sulphur1 charcoal1 and nitre1 when they are chemically combined2 or1 in briefer language1 we have noticed the difference between the mechanical mixture1 and some of the chemical combinations1 of three important elements4 ,our very slight and partial examination of three simple bodies does not1 however1 afford us any deep insight into the principles of chemistry2 we have1 as it were1 only mastered the signification of a few words in a language2 we might know that chien was the ,french for dog1 or cheval horse1 or homme man2 but that knowledge would not be the acquisition of the ,french language1 because we must first know the alphabet1 and then the combination of these letters into words2 we must also acquire a knowledge of the proper arrangement of these words into sentences1 or grammar1 both syntax and prosody1 before we can claim to be a ,french scholar3 so it is with chemistry--any number of isolated experiments with various chemical substances would be comparatively useless1 and therefore the alphabet of chemistry1 or table of simple elements1 must first be acquired4 ,these bodies are understood to be solids1 fluids1 and gases1 which have hitherto defied the most elaborate means employed to reduce them into more than one kind of matter4 ,even pure light is separable into seven parts--viz41 red1 orange1 yellow1 green1 blue1 indigo1 and violet2 but the elements we shall now enumerate are not of a compound1 but1 so far as we know1 of an absolutely simple or single nature2 they represent the boundaries1 not the finality1 of the knowledge that may be acquired respecting them4 ,the elements are sixty-four in number1 of which about forty are tolerably plentiful1 and therefore common2 whilst the remainder1 twenty-four1 are rare1 and for that reason of a lesser utility3 whenever ,nature employs an element on a grand scale it may certainly be called common1 but it generally works for the common good of all1 and fulfils the most important offices4 ,page #hf ,,classification ,,of ,,the ,,alphabet ,,of ,,chemistry4 #ac ,non-,metallic ,bodies4 ,name4 ,symbol4 ,combining proportion or atomic weight4 #a4 ,oxygen ,o #h #b4 ,hydrogen ,h #a #c4 ,nitrogen ,n #ad #d4 ,chlorine ,cl #ce4e #e4 ,iodine ,i #abg4a #f4 ,bromine ,br #hj4 #g4 ,fluorine ,f #ah4i #h4 ,carbon ,c #f #i4 ,boron ,b #aj4i #aj4 ,sulphur ,s #af #aa4 ,phosphorus ,p #cb #ab4 ,silicon ,si #ba4c #ac4 ,selenium ,se #ci4e #ea ,metals4 #a4 ,aluminum ,al #ac4g #b4 ,antimony ,sb #abi #c4 ,arsenic ,as #ge #d4 ,barium ,ba #fh4e #e4 ,bismuth ,bi #bac #f4 ,cadmium ,cd #ef #g4 ,calcium ,ca #bj #h4 ,cerium ,ce #dg #i4 ,chromium ,cr #bf4g #aj4 ,cobalt ,co #bi4e #aa4 ,copper ,cu #ca4g #ab4 ,donarium #ac4 ,didymium ,d #ad4 ,erbium ,e #ae4 ,gold ,au #aig #af4 ,glucinum ,gl #ag4 ,iron ,fe #bh #ah4 ,ilmenium ,il #ai4 ,iridium ,ir #ii #bj4 ,lead ,pb #ajc4g #ba4 ,lanthanium ,la #bb4 ,lithium ,li #f4e #bc4 ,magnesium ,mg #ab4b #bd4 ,manganese ,mn #bg4f #be4 ,mercury ,hg #ajj #bf4 ,molybdenum ,mo #df #bg4 ,nickel ,ni #bi4f #bh4 ,norium #bi4 ,niobium ,nb #cj4 ,osmium ,os #ii4f #ca4 ,platinum ,pt #ih4g #cb4 ,potassium ,k #ci4b #cc4 ,palladium ,pd #ec4c #cd4 ,pelopium ,pe #ce4 ,rhodium ,r #eb4b #cf4 ,rhuthenium ,ru #eb4b #cg4 ,silver ,ag #ajh4a #ch4 ,sodium ,na #bc #ci4 ,strontium ,sr #dc4h #dj4 ,tin ,sn #ei #da4 ,tantalum ,ta #ahd #db4 ,tellurium ,te #fd4b #dc4 ,terbium ,tb #dd4 ,thorium ,th #ei4f #de4 ,titanium ,ti #be #df4 ,tungsten ,w,a #ie #dg4 ,uranium ,u #fj #dh4 ,vanadium ,v #fh4f #di4 ,yttrium ,y #ej4 ,zinc ,zn #cb4f #ea4 ,zirconium ,zr #bb4d 7,n4,b4 ,the elements printed in italics are at present unimportant47 ,footnote ,a3 ,from the mineral ,wolfram1 and now exceedingly valuable1 as when alloyed with iron it is harder than1 and will bore through steel4 ,a few words will suffice to explain the meaning of the terms which head the names1 letters1 and numbers of the ,table of ,elements4 ,page #hg ,the names of the elements have very interesting derivations1 which it is not the object of this work to go into2 the symbols are abbreviations1 ciphers of the simplest kind1 to save time and trouble in the frequent repetition of long words1 just as the signs plus1 and - minus1 are used in algebraic formul4 ,for instance--the constant recurrence of water in chemical combinations must be named1 and would involve the most tedious repetition2 water consists of oxygen and hydrogen1 and by taking the first letter of each word we have an instructive symbol1 which not only gives us an abbreviated term for water1 but also imparts at once a knowledge of its composition by the use of the letters1 ,,ho4 ,again1 to take a more complex example1 such as would occur in the study of organic chemistry--a sentence such as the hydrated oxide of acetule1 is written at once by ,c#d;,h#d,o#b1 the figures referring to the number of equivalents of each element--viz41 #d equivalents of ,c1 the symbol for carbon1 #d of ,h 7hydrogen71 and #b of ,o 7oxygen74 ,the long word paranaphthaline1 a substance contained in coal tar1 is disposed of at once with the symbols and figures ,c#cj;,h#ab4 ,the figures in the third column are1 however1 the most interesting to the precise and mathematically exact chemist4 ,they represent the united labours of the most painstaking and learned chemists1 and are the exact quantities in which the various elements unite4 ,to quote one example3 if #h parts by weight of oxygen--viz41 the combining proportions of that element--are united with #a part by weight of hydrogen1 also its combining number1 the result will be #i parts by weight of water2 but if #h parts of oxygen and #b parts of hydrogen were used1 one only of the latter could unite with the former1 and the result would be the formation again of #i parts of water1 with an overplus of #a equivalent of hydrogen4 ,it is useless to multiply examples1 and it is sufficient to know that with this table of numbers the figures of analysis are obtained4 ,supposing a substance contained #bg parts of water1 and the oxygen in this had to be determined1 the rule of proportion would give it at once1 #i3 #bg33 #h3 #bd4 #i parts of water are to #bg parts as #h of oxygen 7the quantity contained in #i parts of water7 are to the answer required--viz41 #bd of oxygen4 ,the names1 symbols1 and combining proportions being understood1 we may now proceed with the performance of many interesting ,,chemical ,,experiments4 ,as the permanent gases head the list1 they will first engage our attention1 beginning with the element oxygen--,symbol ,o1 combining proportion #h4 ,there is nothing can give a better idea of the enormous quantity of oxygen present in the animal1 vegetable1 and mineral kingdoms1 than the statement that it represents one-third of the weight of the whole crust of the globe4 ,silica1 or flint1 contains about half its weight of oxygen2 lime contains forty per cent42 alumina about thirty-three per cent4 ,in these substances the element oxygen remains inactive and powerless1 chained by the strong fetters of chemical affinity to ,page #hh the silicium of the flint1 the calcium of the lime1 and the aluminum of the alumina4 ,if these substances are heated by themselves they will not yield up the large quantity of oxygen they contain4 ,nature1 however1 is prodigal in her creation1 and hence we have but to pursue our search diligently to find a substance or mineral containing an abundance of oxygen1 and part of which it will relinquish by what used to be called by the old alchemists the torture of heat4 ,such a mineral is the black oxide of manganese1 or more correctly the binoxide of manganese1 which consists of one combining proportion of the metal manganese--viz41 #bg4f1 and two of oxygen--viz41 #h #b #af4 ,if three proportions of the binoxide of manganese are heated to redness in an iron retort1 they yield one proportion 7equal to #h7 of oxygen1 and all that has just been explained by so many words is comprehended in the symbols and figures below3-- #c ,mn,o#b ,mn#c,o#d ,o4 ,thus the #c ,mn,o#b represent the three proportions of the binoxide of manganese before heat is applied1 whilst the sign 1 the sign of equation 7equal to71 is intended to show that the elements or compounds placed before it produce those which follow it2 hence the sequel ,mn#c,o#d ,o shows that another compound of the metal and oxygen is produced1 whilst the ,o indicates the liberated oxygen gas4 ,the iron retort employed to hold the mineral should be made of cast iron in preference to wrought iron1 as the latter is very soon worn out by contact with oxygen at a red heat4 ,a gun-barrel will answer the purpose for an experiment on the small scale1 to which must be adapted a cock and piece of pewter tubing4 ,such a make-shift arrangement may do very well when nothing better offers2 but as a question of expense1 it is probably cheaper in the end to order of ,messrs4 ,simpson and ,maule1 or of ,messrs4 ,griffin1 or of ,messrs4 ,bolton1 a cast-iron bottle1 or cast-iron retort1 as it is termed1 of a size sufficient to prepare two gallons of oxygen from the binoxide of manganese1 which1 with four feet of iron conducting-pipe1 and connected to the bottle with a screw1 does not ,page #hi cost more than six shillings--an enormous dip1 perhaps1 in the juvenile pocket1 and therefore we shall indicate presently a still cheaper apparatus for the same purpose4 7,fig4 #ic47 ,illustration3 ,fig4 #ic4 ,a4 ,the iron bottle1 containing the black oxide of manganese1 with pipe passing to the pneumatic trough1 ,b ,b1 in which is fixed a shelf1 ,c1 perforated with a hole1 under which the end of the pipe is adjusted1 and the gas passes into the gas-jar1 ,d4 ,illustration3 ,fig4 #id4 ,a ,a4 ,pneumatic trough1 with gas jar raised to shelf2 bubbles of air are rushing in at ,b1 as the level of the water is below the shelf--viz41 at ,c ,c4 ,d ,d4 ,same trough and gas jar with water kept over the shelf by the introduction of the stone pitcher ,e1 full of water4 ,the oxygen is conveyed to a square tin box provided with a shelf at one end1 perforated with several holes at least one inch in diameter1 called the pneumatic trough2 any wooden trough1 butter or wash-tub1 foot-pan or bath1 provided with a shelf1 may be raised by the same title to the dignity of a piece of chemical apparatus4 ,the gas jar must be filled with water by withdrawing the stopper and pressing it down into the trough1 and when the neck is below the level of the water1 the stopper is again inserted1 and the jar with the water therein contained lifted steadily on to the shelf1 the entry of atmospheric air being prevented by keeping the lower part of the gas jar1 called the welt1 under the water4 ,sometimes the pneumatic trough contains so small a quantity of water that on raising the gas jar to the shelf the liquid does not cover the bottom1 and the air rushes up in large bubbles4 ,under these circumstances it is better to provide a gallon stone jug full of water1 so that when the jar is being raised to the shelf it may be thrust into the trough 7on the same principle as the crow and the pitcher in the fable71 and thus by its bulk 7as the stones in the pitcher7 raise the water to the proper level4 ,when the gas jar is about half filled with gas the jug may be withdrawn4 ,this arrangement saves the trouble of constantly adding and baling out water from the pneumatic trough4 7,fig4 #id47 ,there are other solid oxygenized bodies in which the affinities are less powerful1 and hence a lower degree of heat suffices to liberate the oxygen gas1 and one of the most useful in this respect is the salt termed chlorate of potash4 ,if the substance is heated by itself1 the temperature required to expel the oxygen is almost as high as that demanded for the black oxide of manganese2 but1 strange to say1 if the two substances are reduced to powder1 and mixed in equal quantities by weight1 then a very moderate increase of heat is sufficient to cause the chlorate of ,page #ij potash to give up its oxygen1 whilst the oxide of manganese undergoes no change whatever4 ,it seems to fulfil only a mechanical office--possibly that of separating each particle of chlorate of potash from the other1 so that the heat attacks the substance in detail1 just as a solid square of infantry might repel almost any attack1 whilst the same body dispersed over a large space might be of little use2 so with the chlorate of potash1 which undergoes rapid decomposition when mixed with and divided amongst the particles of the oxide of manganese2 less so with the red oxide of iron1 and still less with sand or brick-dust4 7,fig4 #ie47 ,illustration3 ,fig4 #ie4 ,preparation of oxygen from chlorate of potash and oxide of manganese4 ,,ko4,cl,o#e ,o#f ,k,cl4 ,this curious fact is explained usually by reference to what is called catalytic action1 or decomposition by contact 7,greek3 kata1 downwards1 and ,greek3 lu1 ,i unloosen71 being a power possessed by a body of resolving another into a new compound without undergoing any change itself4 ,to make this term still clearer1 we may notice another example in linen rags1 which may be exposed for any length of time to the action of water without fear of conversion into sugar2 if1 however1 oil of vitriol is first added to the linen rags1 and they are subsequently digested at a proper temperature with water1 then the rags are converted into sugar 7the author has seen a specimen made of an old shirt72 but1 curious to relate1 the oil of vitriol is unchanged in the process1 and if the process be commenced with a pound of acid1 the same quantity is discoverable at the end of the chemical decomposition of the linen rags1 and their conversion into sugar4 ,if a mixture of equal parts of oxide of manganese and chlorate of potash is placed in a clean ,florence flask1 with a cork1 and pewter1 or glass tube attached1 great quantities of oxygen are quickly liberated1 on the application of the heat of a spirit lamp4 ,such a retort would cost about fourpence1 and if the flask is broken in the operation it can be easily replaced by another1 value one penny1 as the same cork and tube will generally suit a number of these cheap glass vessels4 ,corks may always ,page #ia be softened by using either a proper cork squeezer1 or by placing them under a piece of board or a flat surface1 and rolling and pressing the cork till quite elastic4 ,whilst fitting the latter into the neck of a flask1 it is perhaps safer to hold the thin and fragile vessel in a cloth1 so that if the flask breaks the chemical experiment may not be arrested for many days by the severe cutting and wounding of the fingers4 ,after the cork is fitted1 it is to be removed from the flask and bored with a cork borer4 ,this useful tool is sold in complete sets to suit all sizes of glass tubes1 and the pewter or glass being inserted1 the flask and tube will be ready for use1 provided the tube is bent to the proper curve4 ,this is easy enough to perform with the pewter1 but not quite so easy with the glass tube1 which must be held over the flame of a spirit lamp till soft1 and then bent very gradually to the proper curve4 ,if a short length of the glass tube is heated1 it bends too sharply1 and the convexity of the glass is flattened1 whilst the internal diameter of the tube is lessened1 so that at least three inches in length should be warmed1 and the heat must not be continued in one place only1 but should be maintained in the direction of the bend1 the whole manipulation being conducted without any hurry4 7,fig4 #if47 ,illustration3 ,fig4 #if4 ,a4 ,the cork squeezer4 ,b4 ,the cork borers4 ,c4 ,the operation of bending the glass tube over the flame of the spirit-lamp4 ,d4 ,the neck of the flask1 with cork and tube bent and fitted complete for use4 ,having filled a gas jar with oxygen1 it may be removed from the pneumatic trough by sliding it into a plate under the surface of the water1 and to prevent the stopper being thrust out accidentally from the jar by the upward pressure of the gas1 whilst a little compressed1 during the act of passing it into the plate1 it is advisable to hold the stopper of the jar firmly but gently1 so that it cannot slip out of its place4 ,a number of jars of oxygen may be prepared and arranged in plates1 all of which of course must contain a little water1 and enough to cover the welt of the jar4 ,page #ib ,,experiments ,,with ,,oxygen ,,gas4 ,this gas was originally discovered by ,priestley1 in ,august1 #aggd1 and was first obtained by heating red precipitate--i4e41 the red oxide of mercury4 ,hg,o ,hg ,o4 ,we leave these symbols and figures to be deciphered by the youthful philosopher with the aid of the table of elements1 c41 and return to the experiments4 ,there are certain thin wax tapers like waxed cord1 called bougies1 which can be bent to any shape1 and are very convenient for experiments with the gases4 ,if one of these tapers is bent as in ,fig4 #ig1 then lighted and allowed to burn for some minutes1 a long snuff is gradually formed1 which remains in a state of ignition when the flame of the taper is blown out4 ,on plunging this into a jar of oxygen1 it instantly re-lights with a sort of report1 and burns with greatly-increased brilliancy1 as described by ,dr4 ,priestley in his first experiment with this gas1 and so elegantly repeated by ,professor ,brande in his refined dissertation on the progress of chemical science4 ,illustration3 ,fig4 #ig4 ,the #ast of ,august1 #aggd1 is a red-letter day in the annals of chemical philosophy1 for it was then that ,dr4 ,priestley discovered dephlogisticated air4 ,some1 sporting in the sunshine of rhetoric1 have called this the birthday of pneumatic chemistry2 but it was even a more marked and memorable period2 it was then 7to pursue the metaphor7 that this branch of science1 having eked out a sickly and infirm infancy in the ill-managed nursery of the early chemists1 began to display symptoms of an improving constitution1 and to exhibit the most hopeful and unexpected marks of future importance4 ,the first experiment1 which led to a very satisfactory result1 was concluded as follows3--,a glass jar was filled with quicksilver1 and inserted in a basin of the same2 some red precipitate of quicksilver was then introduced1 and floated upon the quicksilver in the jar2 heat was applied to it in this situation with a burning-lens1 and to use ,priestley's own words1 ,i presently found that air was expelled from it very readily4 ,having got about three or four times as much as the bulk of my materials1 ,i admitted water into it1 and found that it was not imbibed by it4 ,but what surprised me more than ,i can well express was1 that a candle burned in this air with a remarkably vigorous flame1 very much like that enlarged flame with which a candle burns in nitrous air exposed to iron or lime of sulphur 7i4e41 laughing gas72 but as ,i had got nothing like this remarkable appearance from any kind of air besides this peculiar ,page #ic modification of nitrous air1 and ,i knew no nitrous acid was used in the preparation of mercurius calcinatus1 ,i was utterly at a loss how to account for it4 7,fig4 #ih47 ,illustration3 ,fig4 #ih4 ,a4 ,glass vessel full of mercury1 containing the red precipitate at the top1 and standing in the dish ,b1 also containing mercury4 ,c4 ,the burning-glass concentrating the sun's rays on the red precipitate1 being ,priestley's original experiment4 ,second ,experiment4 ,the term oxygen is derived from the ,greek 7,greek3 ozus1 acid1 and ,greek3 genna1 ,i give rise to71 and was originally given to this element by ,lavoisier1 who also claimed its discovery2 and if this honour is denied him1 surely he has deserved equal scientific glory in his masterly experiments1 through which he discovered that the mixture of forty-two parts by measure of azote1 with eight parts by measure of oxygen1 produced a compound precisely resembling our atmosphere4 ,the name given to oxygen was founded on a series of experiments1 one of which will now be mentioned4 ,illustration3 ,fig4 #ii4 ,a4 ,the deflagrating spoon1 ,b4 ,the cork4 ,c4 ,the zinc1 or brass1 or tin plate4 ,d ,d4 ,the gas jar4 ,place some sulphur in a little copper ladle attached to a wire1 and called a deflagrating spoon1 passed through a round piece of zinc or brass plate and cork1 so that the latter acts as an adjusting arrangement to fix the wire at any point required4 ,the combustion of the sulphur1 previously feeble1 now assumes a remarkable intensity1 and a peculiar coloured light is generated1 whilst the sulphur unites with the oxygen1 and forms sulphurous acid gas4 ,it produces1 in fact1 the same gas which is formed by burning an ordinary sulphur match4 ,this compound is valuable as a disinfectant1 and is a very important bleaching agent1 being most extensively employed in the whitening of straw employed in the manufacture of straw bonnets4 ,it is an acid gas1 as ,lavoisier found1 and this property may be detected by pouring a little tincture of litmus into the bottom of the plate in which the gas jar stands4 ,the blue colour of the litmus is rapidly changed to red1 and it might be thought that no further argument could possibly be required to prove that oxygen was the acidifying agent1 the more particularly as the result is the same in the next illustration4 ,page #id ,third ,experiment4 ,cut a small piece from an ordinary stick of phosphorus under water1 take care to dry it properly with a cloth1 and after placing it in a deflagrating spoon1 remove the stopper from the gas-jar1 as there is no fear of the oxygen rushing away1 because it is somewhat heavier than atmospheric air2 and then1 after placing the spoon with the phosphorus in the neck of the jar1 apply a heated wire and pass the spoon at once into the middle of the oxygen2 in a few seconds a most brilliant light is obtained1 and the jar is filled with a white smoke2 as this subsides1 being phosphoric acid1 and perfectly soluble in water1 the same litmus test may be applied1 when it is in like manner changed to red4 ,the acid obtained is one of the most important constituents of bone4 ,fourth ,experiment4 ,a bit of bark-charcoal bound round with wire is set on fire either by holding it in the flame of a spirit-lamp1 or by attaching a small piece of waxed cotton to the lower part1 and igniting this2 the charcoal may then be inserted into a bottle of oxygen1 when the most brilliant scintillations occur4 ,after the combustion has ceased and the whole is cool1 a little tincture of litmus may also be poured in and shaken about1 when it likewise turns red1 proving for the third time the generation of an acid body1 called carbonic acid--an acid1 like the others already mentioned1 of great value1 and one which ,nature employs on a stupendous scale as a means of providing plants1 c41 with solid charcoal4 ,carbonic acid1 a virulent poison to animal life1 is1 when properly diluted1 and as contained in atmospheric air1 one of the chief alimentary bodies required by growing and healthy plants4 ,in three experiments acid bodies have been obtained2 can we speculate on the result of the next8 ,fifth ,experiment4 ,into a deflagrating spoon place a bit of potassium1 set this on fire by holding it in the spoon in the flame of a spirit-lamp1 and then rapidly plunge the burning metal into a bottle of oxygen4 ,a brilliant ignition occurs in the deflagrating spoon for a few seconds1 and there is little or no smoke in the jar4 ,the product this time is a solid1 called potash1 and if this be dissolved in water and filtered1 it is found to be clear and bright1 and now on the addition of a little tincture of litmus to one half of the solution1 it is wholly unaffected1 and remains blue2 but if with the other half a small quantity of tincture of turmeric is mixed1 it immediately changes from a bright yellow solution to a reddish-brown1 because turmeric is one of the tests for an alkali2 and thus is ascertained by the help of this and other tests that the result of the combustion is not an acid1 but an alkali4 ,the experiment is made still more satisfactory by burning another bit of potassium in oxygen and dissolving the product in water1 and if any portion of ,page #ie the reddened liquid derived from the sulphurous1 phosphoric1 and carbonic acids taken from the previous experiments1 be added to separate portions of the alkaline solution1 they are all restored to their original blue colour1 because an acid is neutralized by an alkali2 and the experiment is made quite conclusive by the restoration of the reddened turmeric to a bright yellow on the addition of a solution of either of the three acids already named4 ,moreover1 an acid need not contain a fraction of oxygen1 as there is a numerous class of hydracids1 in which the acidifying principle is hydrogen instead of oxygen1 such as the hydrochloric1 hydriodic1 hydro-bromic1 and hydrofluoric acids4 ,sixth ,experiment4 ,a piece of watch-spring is softened at one end1 by holding it in the flame of a spirit-lamp1 and allowing it to cool4 ,a bit of waxed cotton is then bound round the softened end1 and after being set on fire1 is plunged into a gas jar containing oxygen2 the cotton first burns away1 and then the heat communicates to the steel1 which gradually takes fire1 and being once well ignited1 continues to burn with amazing rapidity1 forming drops of liquid dross1 which fall to the bottom of the plate--and also a reddish smoke1 which condenses on the sides of the jar2 neither the dross which has dropped into the plate1 nor the reddish matter condensed on the jar1 will affect either tincture of litmus or turmeric2 they are neither acid nor alkaline1 but neutral compounds of iron1 called the sesquioxide of iron 7,fe#b,o#c71 and the magnetic oxide 7,fe#c,o#d;,fe,o4,fe#b,o#c74 ,seventh ,experiment4 ,illustration3 ,fig4 #ajj4 ,a4 ,bladder containing oxygen1 provided with a stop-cock and jet leading to1 ,b1 ,b4 ,finger glass containing boiling water4 ,c4 ,the cup of melted phosphorus under the water4 ,the gas escapes from the bladder when pressed4 ,some oxygen gas contained in a bladder provided with a proper jet may be squeezed out1 and upon1 some liquid phosphorus contained in a cup at the bottom of a finger glass full of boiling water1 when a most brilliant combustion occurs1 proving that so long as the principle is complied with--viz41 that of furnishing oxygen to a combustible substance--it will burn under water1 provided it is insoluble1 and possesses the remarkable affinity for oxygen which belongs to phosphorus4 ,the experiment should be performed with boiling water1 to keep the phosphorus in the liquid state2 and it is quite as well to hold a ,page #if square foot of wire gauze over the finger glass whilst the experiment is being performed4 7,fig4 #ajj47 ,eighth ,experiment4 ,oxygen is available from many substances when they are mixed with combustible substances1 and hence the brilliant effects produced by burning a mixture of nitre1 meal powder1 sulphur1 and iron or steel filings2 the metal burns with great brilliancy1 and is projected from the case in most beautiful sparks1 which are long and needle-shaped with steel1 and in the form of miniature rosettes with iron filings2 it is the oxygen from the nitre that causes the combustion of the metal1 the other ingredients only accelerate the heat and rate of ignition of the brilliant iron1 which is usually termed a gerb4 ,ninth ,experiment4 ,a mixture of nitrate of potash1 powdered charcoal1 sulphur1 and nitrate of strontium1 driven into a strong paper case about two inches long1 and well closed at the end with varnish1 being quite waterproof1 may be set on fire1 and will continue to burn under water until the whole is consumed2 the only precaution necessary being to burn the composition from the case with the mouth downward1 and if the experiment is tried in a deep glass jar it has a very pleasing effect4 7,fig4 #aja47 ,illustration3 ,fig4 #aja4 ,a4 ,case of red fire burning downwards1 and attached by a copper wire to a bit of leaden pipe ,b1 to sink it4 ,c ,c4 ,jar containing water4 ,the red-fire composition is made by mixing nitrate of strontia #dj parts by weight1 flowers of sulphur #ac parts1 chlorate of potash #e parts1 sulphuret of antimony #d parts4 ,these ingredients must first be well powdered separately1 and then mixed carefully on a sheet of paper with a paper-knife4 ,they are liable to explode if rubbed together in a mortar1 on account of the presence of sulphur and chlorate of potash1 and the composition1 if kept for any time1 is liable to take fire spontaneously4 ,tenth ,experiment4 ,some zinc is melted in an iron ladle1 and made quite red hot2 if a little dry nitre is thrown upon the surface1 and gently stirred into the metal1 it takes fire with the production of an intense white light1 whilst large quantities of white flakes ascend1 and again descend when cold1 being the oxide of zinc1 and called by the alchemists the ,philosopher's ,wool 7,zn,o74 ,in this experiment the oxygen from the nitre effects the oxidation of the metal zinc4 ,page #ig ,eleventh ,experiment4 ,a mixture of four pounds of nitre with two of sulphur and one and a half of lamp black produces a most beautiful and curious fire1 continually projected into the air as sparks having the shape of the rowel of a spur1 and one that may be burnt with perfect safety in a room1 as the sparks consume away so rapidly1 in consequence of the finely divided condition of the charcoal1 that they may be received on a handkerchief or the hand without burning them4 ,the difficulty consists in effecting the complete mixture of the charcoal4 ,the other two ingredients must first be thoroughly powdered separately1 and again triturated when mixed1 and finally the charcoal must be rubbed in carefully1 till the whole is of a uniform tint of grey and very nearly black1 and as the mixture proceeds portions must be rammed into a paper case1 and set on fire2 if the stars or pinks come out in clusters1 and spread well without other and duller sparks1 it is a sign that the whole is well mixed2 but if the sparks are accompanied with dross1 and are projected out sluggishly1 and take some time to burn1 the mixture and rubbing in the mortar must be continued2 and even that must not be carried too far1 or the sparks will be too small4 ,n4,b4--,if the lamp-black was heated red hot in a close vessel1 it would probably answer better when cold and powdered4 ,twelfth ,experiment4 ,into a tall gas jar with a wide neck project some red-hot lamp-black through a tin funnel1 when a most brilliant flame-like fire is obtained1 showing that finely divided charcoal with pure oxygen would be sufficient to afford light2 but as the atmosphere consists of oxygen diluted with nitrogen1 compounds of charcoal with hydrogen1 are the proper bodies to burn1 to produce artificial light4 ,thirteenth ,experiment4 ,the ,bude ,light4 ,this pretty light is obtained by passing a steady current of oxygen gas 7escaping at a very low pressure7 through and up the centre pipe of an argand oil lamp1 which must be supplied with a highly carbonized oil and a very thick wick1 as the oxygen has a tendency to burn away the cotton unless the oil is well supplied1 and allowed to overflow the wick1 as it does in the lamps of the lighthouses4 ,the best whale oil is usually employed1 though it would be worth while to test the value of ,price's ,belmontine ,oil for the same purpose4 7,fig4 #ajb47 ,illustration3 ,fig4 #ajb4 ,a4 ,reservoir of oil4 ,b4 ,the flexible pipe conveying oxygen to centre of the argand lamp4 ,page #ih ,fourteenth ,experiment4 ,a ,red ,light4 ,clear out the oil thoroughly from the ,bude light apparatus2 or1 what is better1 have two lamps1 one for oil1 and the other for spirit2 fill the apparatus with a solution of nitrate of strontia and chloride of calcium in spirits of wine1 and let it burn from the cotton in the same way as the oil1 and supply it with oxygen gas4 ,fifteenth ,experiment4 ,a ,green ,light4 ,dissolve boracic acid and nitrate of baryta in spirits of wine1 and supply the ,bude lamp with this solution4 ,sixteenth ,experiment4 ,a ,yellow ,light4 ,dissolve common salt in spirits of wine1 and burn it as already described in the ,bude light apparatus4 ,seventeenth ,experiment4 ,the ,oxy-calcium ,light4 ,illustration3 ,fig4 #ajc4--,no4 #a4 ,a4 ,oxygen jet4 ,b4 ,the ball of lime1 suspended by a wire4 ,c4 ,spirit lamp4 ,no4 #b4 ,d4 ,oxygen jet4 ,e4 ,gas 7jet connected with the gas-pipe in the rear by flexible pipe7 projected on to ball of lime1 ,f4 ,this very convenient light is obtained in a simple manner1 either by using a jet of oxygen as a blowpipe to project the flame of a spirit lamp on to a ball of lime2 or common coal-gas is employed instead of the spirit lamp1 being likewise urged against a ball of lime4 ,by this plan one bag containing oxygen suffices for the production of a brilliant light1 not equal1 however1 to the oxy-hydrogen light1 which will be explained in the article on hydrogen4 7,fig4 #ajc47 ,eighteenth ,experiment4 ,to show the weight of oxygen gas1 and that it is heavier than air1 the stoppers from two bottles containing it may be removed1 one bottle may be left open for some time and then tested by a lighted taper1 when it ,page #ii will still indicate the presence of the gas1 whilst the other may be suddenly inverted over a little cup in which some ether1 mixed with a few drops of turpentine1 may be burning--the flame burns with much greater brilliancy at the moment when the oxygen comes in contact with it4 ,nineteenth ,experiment4 ,the theory of the effect of oxygen upon the system when inhaled would be an increase in the work of the respiratory organs2 and it is stated that after inhaling a gallon or so of this gas1 the pulse is raised forty or fifty beats per minute3 the gas is easily inhaled from a large india-rubber bag through an amber mouthpiece2 it must of course be quite pure1 and if made from the mixture of chlorate of potash and oxide of manganese1 should be purified by being passed through lime and water1 or cream of lime4 ,twentieth ,experiment4 ,there are certain colouring matters that are weakened or destroyed by the action of light and other causes1 which deprive them of oxygen gas or deoxidize them4 ,a weak tincture of litmus1 if long kept1 often becomes colourless1 but if this colourless fluid is shaken in a bottle with oxygen gas it is gradually restored2 and if either litmus1 turmeric1 indigo1 orchil1 or madder1 paper1 or certain ribbons dyed with the same colouring matters1 have become faded1 they may be partially restored by damping and placing them in a bottle of oxygen gas4 ,the effect of the oxygen is to reverse the deoxidizing process1 and to impart oxygen to the colouring matters4 ,by a peculiar process indigo may be obtained quite white1 and again restored to its usual blue colour1 either by exposure to the air or by passing a stream of oxygen through it4 ,twenty-first ,experiment4 ,messrs4 ,matheson1 of ,torrington-street1 ,russell-square1 prepare in the form of wire some of the rarest metals1 such as magnesium1 lithium1 c4 ,a wire of the metal magnesium burns magnificently in oxygen gas1 and forms the alkaline earth magnesia4 ,the metal lithium1 to which such a very low combining proportion belongs--viz41 #f4e1 can also be procured in the state of wire1 and burns in oxygen gas with an intense white light into the alkaline lithia1 which dissolved in alcohol with a little acetic acid1 and burnt1 affords a red flame1 making a curious contrast between the effects of colour produced by the metallic and oxidized state of lithium4 ,,the ,,allotropic ,,condition ,,of ,,oxygen ,,gas4 ,the term allotropy 7from ,greek3 allotropos1 of a different nature7 was first used by the renowned chemist ,berzelius4 ,dimorphism1 or diversity in crystalline form1 is therefore a special case of allotropy1 and is most amusingly illustrated with the iodide of mercury 7,hg,i71 which is made either by rubbing together equal combining proportions ,page #ajjof mercury and iodine 7both of which are to be found in the ,table of ,elements1 page #hf71 or by carefully precipitating a solution of corrosive sublimate 7chloride of mercury 7,hg,cl77 with one of iodide of potassium1 just enough and no more of the latter being added to precipitate the metal1 or else the iodide of mercury is redissolved by the excess of the precipitant4 ,it is first of a dirty yellow1 and then gradually changes when stirred to a scarlet2 if this be collected on a filter1 and washed and drained1 it is a beautiful scarlet1 and when some of this substance is rubbed across a sheet of paper1 a bright scarlet is apparent1 which may be rapidly changed to a lemon-yellow by heating the paper over the flame of a spirit lamp2 and the iodide of mercury is again brought back to a scarlet colour by rubbing down the yellow crystals with the fingers4 ,this experiment may be repeated over and over again with the like results4 ,if some of the scarlet iodide of mercury is sublimed from one bit of glass to another1 it forms crystals1 derived from the right rhombic prism2 when these are scratched with a pin they change again to the scarlet state1 the latter when crystallized being in the form of the square-based octohedron4 ,other cases of dimorphism may be mentioned--viz41 with sulphur1 carbonate of lime1 and lead1 and many others1 whilst allotropy is curiously illustrated in the various conditions of charcoal1 which1 in the more numerous examples1 is black and opaque1 and in another instance transparent like water4 ,lamp-black is soft1 but the diamond is the hardest natural substance4 ,the allotropic state of sulphur has been already alluded to2 phosphorus1 again1 exists in three modifications3 #ast1 ,common phosphorus1 which shines in the dark and emits a white smoke4 #bnd1 ,white phosphorus4 #crd1 ,red or amorphous phosphorus1 which does not shine or emit white smoke when exposed to the air1 and is so altered in its properties that it may be safely carried in the pocket4 ,enough evidence has therefore been offered to show that the allotropic property is not confined to one element or compound1 but is discoverable in many bodies1 and in no one more so than in the allotropic state of the element oxygen called ,,ozone4 ,the ,greek language has again been selected by the discoverer1 ,schnbein1 of ,basle1 for the title or name of this curious modification of oxygen1 and it is so termed from ,greek3 oxein1 to smell4 ,the name at once suggests a marked difference between ozone and oxygen1 because the latter is perfectly free from odour1 whilst the former has that peculiar smell which is called electric1 and is distinguishable whenever an electrical machine is at work1 or if a ,leyden jar is charged by the powerful ,rhumkoff1 or ,hearder coil2 it is also apparent when water is decomposed by a current of electricity and resolved into its elements1 oxygen and hydrogen4 ,when highly concentrated it smells like chlorine2 and the author recollects seeing the first experiments by ,schnbein1 in ,england1 at ,mr4 ,cooper's laboratory in the ,blackfriars-road4 ,ozone is prepared by taking a clean empty bottle1 and pouring therein a very ,page #aja little distilled water1 into which a piece of clean scraped phosphorus is introduced1 so as to expose about one-half of its diameter to the air in the bottle1 whilst the other is in contact with the water4 7,fig4 #ajd47 ,for the sake of precaution1 the bottle may stand in a basin or soup plate1 so that if the phosphorus should take fire1 it may be instantly extinguished by pouring cold water into the bottle1 and should this crack and break1 the phosphorus is received into the plate4 ,illustration3 ,fig4 #ajd4 ,a4 ,a quart bottle1 with the stopper loosely placed therein4 ,b4 ,the stick of clean phosphorus4 ,c4 ,the water level just to half the thickness of the phosphorus4 ,d ,d4 ,a soup-plate4 ,when the ozone is formed the phosphorus can be withdrawn1 and the phosphorous-acid smoke washed out by shaking the bottle2 it is distinguishable by its smell1 and also by its action on test paper1 prepared by painting with starch containing iodide of potassium on some ,bath post paper2 when this is placed in the bottle containing ozone1 it changes the test blue1 or rather a purplish blue4 ,illustration3 ,fig4 #aje4 ,v4 ,a small voltaic battery standing on the stool with glass legs1 ,s ,s1 and capable of heating a thin length of platinum wire about two inches long1 and bent to form a point between the conducting wires1 ,w ,w4--,n4,b4 ,the voltaic current can be cut off at pleasure1 so as to cool the wire when necessary4 ,a is the prime conductor of an ordinary cylinder electrical machine4 ,b is the wire conveying the frictional electricity to the conducting wires of the voltaic battery1 where the point ,p being the sharpest point in the arrangement1 delivers the electrified and ozonized air4 ,ozone is a most energetic body1 and a powerful bleaching agent2 if a point is attached to the prime conductor of an electrical machine1 and the electrified air is received into a bottle1 it will be found to smell1 and has the power of bleaching a very dilute solution of indigo4 ,ozone ,page #ajb is not a mere creation of fancy1 as it can not only be produced by certain methods1 but may be destroyed by a red heat4 ,if a point is prepared with a loop of platinum wire1 and this latter1 after being connected with a voltaic battery1 made red hot1 and the whole placed on an insulating stool1 and connected with the prime conductor of an electrical machine1 it is found that the electrified air no longer smells1 the ozone is destroyed2 on the other hand1 if the voltaic battery is disconnected1 and the electrified air again allowed to pass from the cold platinum wire1 the smell is again apparent1 the air will bleach1 and if caused to impinge at once upon the iodide of starch test1 changes it in the manner already described4 7,fig4 #aje47 ,ozone is insoluble in water1 and oxidizes silver and lead leaf1 finely powdered arsenic and antimony2 it is a poison when inhaled in a concentrated state1 whilst diluted1 and generated by natural processes1 it is a beneficent and beautiful provision against those numerous smells originating from the decay of animal and vegetable matter1 which might produce disease or death3 ozone is therefore a powerful disinfectant4 ,the test for ozone is made by boiling together ten parts by weight of starch1 one of iodide of potassium1 and two hundred of water2 it may either be painted on ,bath post paper1 and used at once1 or blotting paper may be saturated with the test and dried1 and when required for use it must be damped1 either before or after testing for ozone1 as it remains colourless when dry1 but becomes blue after being moistened with water4 ,paper prepared with sulphate of manganese is an excellent test for ozone1 and changes brown rapidly by the oxidation of the proto-salt of manganese1 and its conversion into the binoxide of the metal4 ,ozone is also prepared by pouring a little sulphuric ether into a quart bottle1 and then1 after heating a glass rod in the flame of the spirit lamp1 it may be plunged into the bottle1 and after remaining there a few minutes ozone may be detected by the ordinary tests4 ,,nitrogen1 ,,or ,,azote4 ,greek3 ,nitron1 nitre2 ,greek3 genna1 ,i form2 ,greek3 a1 privative2 ,greek3 z1 life4 ,symbol1 ,n2 combining proportion1 #ad4 ,also termed by ,priestley1 phlogisticated air4 ,in the year #aggb1 ,dr4 ,rutherford1 ,professor of ,botany in the ,university of ,edinburgh1 published a thesis in ,latin on fixed air1 in which he says3--,by the respiration of animals healthy air is not merely rendered mephitic 7i4e41 charged with carbonic acid gas71 but also suffers another change4 ,for after the mephitic portion is absorbed by a caustic alkaline lixivium1 the remaining portion is not rendered salubrious2 and although it occasions no precipitate in lime-water1 it nevertheless extinguishes flame and destroys life4 ,such is the doctor's account of the discovery of nitrogen1 which may be separated from the oxygen in the air in a very simple manner4 ,the atmosphere is the great storehouse of nitrogen1 and four-fifths of its prodigious volume consist of this element4 ,page #ajc ,composition of ,atmospheric ,air4 ,bulk4 ,weight4 ,oxygen #bj #bb4c ,nitrogen #hj #gg4g --- ---- #ajj #ajj4 ,the usual mode of procuring nitrogen gas is to abstract or remove the oxygen from a given portion of atmospheric air1 and the only point to be attended to1 is to select some substance which will continue to burn as long as there is any oxygen left4 ,thus1 if a lighted taper is placed in a bottle of air1 it will only burn for a certain period1 and is gradually and at last extinguished2 not that the whole of the oxygen is removed or changed1 because after the taper has gone out1 some burning sulphur may be placed in the vessel1 and will continue to burn for a limited period2 and even after these two combustibles have1 as it were1 taken their fill of the oxygen1 there is yet a little left1 which is snapped up by burning phosphorus1 whose voracious appetite for oxygen is only appeased by taking the whole4 ,it is for this reason that phosphorus is employed for the purpose of removing the oxygen1 and also because the product 7phosphoric acid7 is perfectly soluble in water1 and thus the oxygen is first combined1 and then washed out of a given volume of air1 leaving the nitrogen behind4 ,first ,experiment4 ,to prepare nitrogen gas1 it is only necessary to place a little dry phosphorus in a ,berlin porcelain cup on a wine glass1 and to stand them in a soup plate containing water4 ,the phosphorus is set on fire with a hot wire1 and a gas jar or cylindrical jar is then carefully placed over it1 so that the welt of the jar stands in the water in the soup plate4 ,at first1 expansion takes place in consequence of the heat1 but this effect is soon reversed1 as the oxygen is converted into a solid by union with the phosphorus1 forming a white smoke1 which gradually disappears4 7,fig4 #ajf47 ,illustration3 ,fig4 #ajf4 ,a4 ,cylindrical glass vessel1 open at one end1 and inverted over ,b1 the wine-glass1 supporting ,c1 the cup containing the burning phosphorus1 and the whole standing in a soup-plate1 ,d ,d1 containing water4 ,supposing two grains of phosphorus had been placed in a platinum tube1 and just enough atmospheric air passed over it to convert the whole into phosphoric acid1 the weight of the phosphorus would be increased to #d grains by the addition of #b grains of oxygen2 ,page #ajd now one cubic inch of oxygen weighs #j4cdai1 or about #a_/crd of a grain1 hence #g4c cubic inches of oxygen disappear1 which weigh as nearly as possible #b grains1 so that as #cf4e cubic inches of air contain #g4c cubic inches of oxygen1 that quantity of air must have passed over the #b grains of phosphorus to convert it into #d grains of phosphoric acid4 ,for very delicate purposes1 nitrogen is best prepared by passing air over finely-divided metallic copper heated to redness2 this metal absorbs the whole of the oxygen and leaves the nitrogen4 ,the finely-divided copper is procured by passing hydrogen gas over pure black oxide of copper4 ,second ,experiment4 ,illustration3 ,fig4 #ajg4 ,a4 ,glass jar1 with collar of leather1 through which the stamper1 ,c1 works4 ,b ,b4 ,the tube containing the finely-divided lead1 part of which falls out1 and is ignited1 and retained by the little tray just below1 being part of the iron stand1 ,d ,d1 with crutches supporting the ends of the glass tube1 and the whole stands in the dish of water1 ,e ,e4 ,a very instructive experiment is performed by heating a good mass of tartrate of lead in a glass tube which is hermetically sealed1 and being placed on an iron support1 is then covered by a capped air jar with a sliding rod and stamper1 the whole being arranged in a plate containing water4 ,when the stamper is pushed down upon the glass the latter is broken 7,fig4 #ajg71 and the air gradually penetrates to the finely divided lead1 when ignition occurs1 and the oxygen is absorbed1 as demonstrated by the rise of the water in the jar4 ,on the same principle1 if a bottle is filled about one-third full with a liquid amalgam of lead and mercury1 and then stopped and shaken for two hours or more1 the finely divided lead absorbs the oxygen and leaves pure nitrogen4 ,or if a mixture of equal weights of sulphur and iron filings1 is made into a paste with water in a thin iron cup1 and then warmed and placed under a gas jar full of air standing on the ,page #aje shelf of the pneumatic trough1 or in a dish full of water1 the water gradually rises in the jar in about forty-eight hours1 in consequence of the absorption of the oxygen gas4 ,third ,experiment4 ,nitrogen is devoid of colour1 taste1 smell1 of alkaline or acid qualities2 and1 as we shall have occasion to notice presently1 it forms an acid when chemically united with oxygen1 and an alkali in union with hydrogen4 ,a lighted taper plunged into this gas is immediately extinguished1 while its specific gravity1 which is lighter than that of oxygen or air1 is demonstrated by the rule of proportion4 ,weight of #ajj cubic ,weight of #ajj cubic ,specific inches of air at #fj ,unity4 inches of nitrogen at gravity of ,fahr41 bar4 #bi4ib in4 #fj ,fahr41 bar4 #bi4ib in4 nitrogen4 #cj4hbi 3 #a 33 #bi4ieb 3 #iga ,and its levity may be shown very prettily by a simple experiment4 ,select two gas jars of the same size1 and after filling one with oxygen gas and the other with nitrogen gas1 slide glass plates over the bottoms of the jars1 and proceed to invert the one containing oxygen1 placing the neck in a stand formed of a box open at the top2 then place the jar containing nitrogen over the mouth of the first1 withdrawing the glass plates carefully2 and if the table is steady the top gas jar will stand nicely on the lower one4 ,then 7having previously lighted a taper so as to have a long snuff7 remove the stopper from the nitrogen jar and insert the lighted taper1 which is immediately extinguished1 and as quickly relighted by pushing it down to the lower jar containing the oxygen4 ,this experiment may be repeated several times1 and is a good illustration of the relative specific gravities of the two gases1 and of the importance of the law of universal diffusion already explained at p4 #f1 by which these gases mix1 not combine together1 and the atmosphere remains in one uniform state of composition in spite of the changes going on at the surface of the earth4 ,omitting the aqueous vapour1 or steam1 ever present in variable quantities in the atmosphere1 ten thousand volumes of dry air contain1 according to ,graham3-- ,i,ilustration3 ,fig4 #ajh4 ,a4 ,gas jar containing nitrogen1 ,n1 standing on ,b1 another jar full of oxygen1 ,o4 ,the taper1 ,c1 is extinguished at ,n1 and relighted at ,o4 ,d ,d4 ,stand supporting the jars4 ,page #ajf ,nitrogen #giab ,oxygen #bjhj ,carbonic acid #d ,carburetted hydrogen 7,,ch#b7 #d ,ammonia a trace ------- #aj1jjj ,fourth ,experiment4 ,it was the elegant1 the accomplished1 but ill-fated ,lavoisier who discovered1 by experimenting with quicksilver and air1 the compound nature of the atmosphere2 and it was the same chemist who gave the name of azote to nitrogen2 it should1 however1 be borne in mind that it does not necessarily follow because a gas extinguishes flame that it is a poison4 ,nitrogen extinguishes flame1 but we inhale enormous quantities of air without any ill effects from the nitrogen or azote that it contains2 on the other hand1 many gases that extinguish flame are specific poisons1 such as carbonic acid1 carbonic oxide1 cyanogen1 c4 ,lavoisier's experiment may be repeated by passing into a measured jar1 graduated into five equal volumes1 four measures of nitrogen and one measure of oxygen2 a glass plate should then be slid over the mouth of the vessel1 and it may be turned up and down gently for some little time to mix the two gases1 and when the mixture is tested with a lighted taper1 it is found neither to increase nor diminish the illuminating power and the taper burns as it would do in atmospheric air4 7,fig4 #aji47 ,illustration3 ,fig4 #aji4 ,a4 ,gas jar divided into five equal parts4 ,b ,b4 ,section of pneumatic trough1 to show the decantation of gas from one vessel to another4 ,the gas is being passed from ,c to ,a1 through the water4 ,page #ajg ,,hydrogen4 ,hydrogen 7,greek3 udr1 water2 ,greek3 genna1 ,i give rise to71 so termed by ,lavoisier--called by other chemists inflammable air1 and phlogiston4 ,symbol1 ,h2 combining properties1 #a4 ,the lightest known form of matter4 ,every #ajj parts by weight of water contain #aa parts of hydrogen gas2 and as the quantity of water on the surface of the earth represents at least two-thirds of the whole area1 the source of this gas1 like that of oxygen or nitrogen1 is inexhaustible4 ,van ,helmont1 ,mayow1 and ,hales had shown that certain inflammable and peculiar gases could be obtained1 but it was reserved for the rigidly philosophic mind of ,cavendish to determine the nature of the elements contained in1 and giving a speciality to1 the inflammable gases of the older chemists4 ,by acting with dilute acids upon iron1 zinc1 and tin1 ,cavendish liberated an inflammable elastic gas2 and he discovered nearly all the properties we shall notice in the succeeding experiments1 and especially demonstrated the composition of water in his paper read before the ,royal ,society in the year #aghd4 ,first ,experiment4 ,hydrogen is prepared in a very simple manner1 by placing some zinc cuttings in a bottle1 to which is attached a cork and pewter or bent glass tube1 and pouring upon the metal some dilute sulphuric or hydrochloric acid4 ,effervescence and ebullition take place1 and the gas escapes in large quantities1 water being decomposed2 the oxygen passes to the zinc1 and forms oxide of zinc1 and this uniting with the sulphuric acid forms sulphate of zinc1 which may be obtained after the escape of the hydrogen by evaporation and crystallization4 7,fig4 #aaj47 ,zn ,,ho4,,so#c ,zn,o4,,so#c ,h2 or1 ,zn ,h,cl ,zn,cl ,h4 ,in nearly all the processes employed for the generation of hydrogen gas1 a metal is usually employed1 and this fact has suggested the notion that hydrogen may possibly be a metal1 although it is the lightest known form of matter2 and it will be observed in all the succeeding experiments that a metallic substance will be employed to take away the oxygen and displace the hydrogen4 ,illustration3 ,fig4 #aaj4 ,a4 ,bottle containing zinc cuttings and water and fitted with a cap and two tubes1 the one marked ,b1 containing a funnel1 conveys the sulphuric acid to the zinc and water1 whilst the gas escapes through the pipe ,c4 ,page #ajh ,whenever hydrogen is prepared it should be allowed to escape from the generating vessel for a few minutes before any flame is applied1 in order that the atmospheric air may be expelled4 ,the most serious accidents have occurred from carelessness in this respect1 as a mixture of hydrogen and air is explosive1 and the more dangerous when it takes fire in any closed glass bottle4 ,second ,experiment4 ,if a piece of potassium is confined in a little coarse wire gauze cage1 attached to a rod1 and thrust under a small jar full of water1 placed on the shelf of the pneumatic trough1 hydrogen gas is produced with great rapidity1 and is received into the gas jar4 ,the bit of potassium being surrounded with water1 is kept cool1 whilst the hydrogen escaping under the water is not of course burnt away1 as it is whenever the metal is thrown on the surface of water4 ,third ,experiment4 ,illustration3 ,fig4 #aaa4 ,a4 ,flask containing water1 and producing steam1 which passes to the iron tube1 ,b ,b1 containing the iron borings heated red hot in the charcoal stove ,c4 ,the hydrogen passes to the jar ,d1 standing on the shelf of the pneumatic trough4 ,across a small iron table-furnace is placed about eighteen inches of #a-;inch gas-pipe containing iron borings1 the whole being red-hot2 and attached to one end is a pipe conveying steam from a boiler1 or flask1 or retort1 whilst another pipe is fitted to the opposite end1 and passes to the pneumatic trough4 ,directly the steam passes over the red hot iron borings it is deprived of oxygen1 which remains with the iron1 forming the rust or oxide of iron1 whilst the hydrogen1 called in this case water gas1 escapes with great rapidity4 ,when steam is passed over red-hot charcoal1 hydrogen is also produced with carbonic oxide gas1 and this in fact is the ordinary process of making water gas1 which being purified is afterwards saturated with some volatile hydrocarbon and burnt4 ,at first sight1 such a mode of making gas would be thought extremely profitable1 and in spite of the numerous failures the discovery 7so called7 of water gas is reproduced as a sort of chronic wonder2 but experience and practice have clearly demonstrated that water gas is a fallacy1 and as long as we can get coal it is not worth while going through the round-about processes of first burning coal to produce steam2 secondly1 ,page #aji of burning coal to heat charcoal1 over which the steam is passed to be converted into gas1 which has then to be purified and saturated with a cheap hydrocarbon obtained from coal or mineral naphtha2 whilst ordinary coal gas is obtained at once by heating coal in iron retorts4 7,fig4 #aaa47 ,thus1 by the metals zinc1 tin1 potassium1 red-hot iron 7and we might add several others71 the oxygen of water is removed and hydrogen gas liberated4 ,fourth ,experiment4 ,if bottles of hydrogen gas are prepared by all the processes described1 they will present the same properties when tested under similar circumstances4 ,a lighted taper applied to the mouths of the bottles of hydrogen1 which should be inverted1 causes the gas to take fire with a slight noise1 in consequence of the mixture of air and hydrogen that invariably takes place when the stopper is removed2 on thrusting the lighted taper into the bulk of the gas it is extinguished1 showing that hydrogen possesses the opposite quality to oxygen--viz41 that it takes fire1 but does not support combustion4 ,by keeping the bottles containing the hydrogen upright1 when the stopper is removed the gas escapes with great rapidity1 and atmospheric air takes its place1 so much so that by the time a lighted taper is applied1 instead of the gas burning quietly1 it frequently astonishes the operator with a loud pop4 ,this sudden attack on the nerves may be prevented by always experimenting with inverted bottles4 7,fig4 #aab47 ,illustration3 ,fig4 #aab4 ,a4 ,bottle opened upright1 and hydrogen exploding4 ,b4 ,bottle opened inverted1 and hydrogen burning quietly at the mouth4 ,fifth ,experiment4 ,hydrogen is #ad4d lighter than air1 and for that reason may be passed into bottles and jars without the assistance of the pneumatic trough4 ,one of the most amusing proofs of its levity is that of filling paper bags or balloons with this gas2 and we read1 in the accounts of the ftes at ,page #aaj ,paris1 of the use of balloons ingeniously constructed to represent animals1 so that a regular aerial hunt was exhibited1 with this drawback only1 that nearly all the animals preferred ascending with their legs upwards1 a circumstance which provoked intense mirth amongst the volatile ,frenchmen4 ,the lightness of hydrogen may be shown in two ways--first1 by filling a little gold-beater's skin balloon with pure hydrogen 7prepared by passing the gas made from zinc and dilute pure sulphuric acid through a strong solution of potash1 and afterwards through one of nitrate of silver71 and allowing the balloon to ascend2 and then afterwards1 having of course secured the balloon by a thin twine or strong thread1 it may be pulled down and the gas inhaled1 when a most curious effect is produced on the voice1 which is suddenly changed from a manly bass to a ludicrous nasal squeaking sound4 ,the only precautions necessary are to make the gas quite pure1 and to avoid flame whilst inhaling the gas4 ,it is related by ,chaptal that the intrepid 7qure1 foolish7 but unfortunate aeronaut1 ,mons4 ,pilate de ,rosio1 having on one occasion inhaled hydrogen gas1 was rash enough to approach a lighted candle1 when an explosion took place in his mouth1 which he says was so violent that he fancied all his teeth were driven out4 ,of course1 if it were possible to change by some extraordinary power the condition of the atmosphere in a concert-room or theatre1 all the bass voices would become extremely nasal and highly comic1 whilst the sopranos would emulate railway whistles and screech fearfully2 and supposing the specific gravity of the air was continually and materially changing1 our voices would never be the same1 but alter day by day1 according to the state of the air1 so that the familiar voice would be an impossibility4 ,a bell rung in a gas jar containing air emits a very different sound from that which is produced in one full of hydrogen--a simple experiment is easily performed by passing a jar containing hydrogen over a self-acting bell1 such as is used for telegraphic purposes4 7,fig4 #aac47 ,illustration3 ,fig4 #aac4 ,a4 ,stand and bell4 ,b ,b4 ,tin cylinder full of hydrogen1 which may be raised or depressed at pleasure1 by lifting it with the knob at the top1 when the curious changes in the sound of the bell are audible4 ,sixth ,experiment4 ,some of the small pipes from an organ may be made to emit the most curious sounds by passing heavy and light gases through them2 in these experiments bags containing the gases should be employed1 which may drive air1 oxygen1 carbonic acid1 or hydrogen1 through the organ pipes at precisely the same pressure4 ,page #aaa ,seventh ,experiment4 ,one of those toys called ,the ,squeaking ,toy affords another and ridiculous example of the effect of hydrogen on sound1 when it is used in a jar containing this gas4 7,fig4 #aad47 ,illustration3 ,fig4 #aad4 ,the squeaking toy1 used in a jar of hydrogen4 ,eighth ,experiment4 ,an accordion played in a large receptacle containing hydrogen gas demonstrates still more clearly what would be the effect of an orchestra shut up in a room containing a mixture of a considerable portion of hydrogen with air1 as the former1 like nitrogen1 is not a poison1 and only kills in the absence of oxygen gas4 ,ninth ,experiment4 ,some very amusing experiments with balloons have been devised by ,mr4 ,darby1 the eminent firework manufacturer1 by which they are made to carry signals of three kinds1 and thus the motive or ascending power may be utilized to a certain extent4 ,mr4 ,darby's attention was first directed to the manufacture of a good1 serviceable1 and cheap balloon1 which he made of paper1 cut with mathematical precision2 the gores or divisions being made equal1 and when pasted together1 strengthened by the insertion of a string at the juncture2 so that the skeleton of the balloon was made of string1 the whole terminating in the neck1 which was further stiffened with calico1 and completed when required by a good coating of boiled oil4 ,these balloons are about nine feet high and five feet in diameter in the widest part1 exactly like a pear1 and tapering to the neck in the most graceful and elegant manner4 ,they retain the hydrogen gas remarkably well for many hours1 and do not leak1 in consequence of the paper of which they are made being well selected and all holes stopped1 and also from the circumstance of the pressure being so well distributed over the interior by the almost mathematical precision with which they are cut1 and the careful preparation of the paper with proper varnish4 ,one of their greatest recommendations is cheapness2 for whilst a gold-beater's skin balloon of the same size would cost about #el41 these can be furnished at #es4 each in large quantities4 ,a balloon required to carry one or more persons must be constructed of the best materials1 and cannot be too carefully made2 it is therefore a somewhat costly affair1 and as much as #bjjl41 #ejjl41 and even #ajjjl4 have been expended in the construction of these aerial chariots4 ,the chief points requiring attention are3--first1 the quality of the silk2 secondly1 the precision and scrupulous nicety required in cutting ,page #aab out and joining the gores2 thirdly1 the application of a good varnish to fill up the pores of the silk1 which must be insoluble in water1 and sufficiently elastic not to crack4 ,the usual material is ,indian silk 7termed ,corah silk71 at from #bs4 to #bs4 #f;d4 per yard4 ,the gores or parts with which the balloon is constructed require1 as before stated1 great attention2 it being a common saying amongst aeronauts1 that a cobweb will hold the gas if properly shaped the object being to diffuse the pressure equally over the whole bag or balloon4 ,the varnish with which the silk is rendered air-tight can be made according to the private recipe of ,mr4 ,graham1 an aeronaut1 who states that he uses for this purpose two gallons of linseed oil 7boiled71 two ditto 7raw71 and four ounces of beeswax2 the whole being simmered together for one hour1 answers remarkably well1 and the varnish is tough and not liable to crack4 ,for repairing holes in a balloon1 ,mr4 ,graham recommends a cement composed of two pounds of black resin and one pound of tallow1 melted together1 and applied on pieces of varnished silk to the apertures4 ,the actual cost of a balloon will be understood from information also derived from ,mr4 ,graham4 ,his celebrated ,victoria ,balloon1 which has passed through so many hairbreadth escapes1 was sixty-five feet high1 and thirty-eight feet in diameter in the broadest part2 and the following articles were used in its construction3-- s4 d4 #adjj yards of ,corah silk1 at #bs4 #f;d4 per yard #age #j #j ,the netting weighed #gj lbs4 #bj #j #j ,extra ropes weighed #bj lbs4 at #bs4 per lb4 #b #j #j ,the car weighed #be lbs4 #g #j #j ,varnish1 wages1 c4 #af #j #j ------------- #bbj #j #j ,thirty-eight thousand cubic feet of coal gas were required to fill this balloon1 charged by one company #bjl41 by others from #il4 to #ajl42 and eight men were required to hold the inflated baggy monster4 ,such a balloon as described above is a mere soap bubble when compared with the ,new ,aerial ,ship now building in the vicinity of ,new ,york2 the details are so practical and interesting1 that we quote nearly the whole account of this mammoth or ,great ,eastern amongst balloons1 as given in the ,new ,york ,times4 ,an experiment in scientific ballooning1 greater than has yet been undertaken1 is about to be tried in this city4 ,the project of crossing the ,atlantic ,ocean with an air-ship1 long talked of1 but never accomplished1 has taken a shape so definite that the apparatus is already prepared and the aeronaut ready to undertake his task4 ,the work has been conducted quietly1 in the immediate vicinity of ,new ,york1 since the opening of spring4 ,the new air-ship1 which has ,page #aac been christened the ,city of ,new ,york1 is so nearly completed1 that but few essentials of detail are wanting to enable the projectors to bring it visibly before the public4 ,the aeronaut in charge is ,mr4 ,t4 ,s4 ,c4 ,lowe1 a ,new ,hampshire man1 who has made thirty-six balloon ascensions4 ,the dimensions of the ,city of ,new ,york so far exceed those of any balloon previously constructed1 that the bare fact of its existence is notable4 ,briefly1 for so large a subject1 the following are the dimensions3--,greatest diameter1 #acj feet2 transverse diameter1 #ajd feet2 height1 from valve to boat1 #cej feet2 weight1 with outfit1 #c tons2 lifting power 7aggregate71 #bb tons2 capacity of gas envelope1 #gbe1jjj cubic feet4 ,the ,city of ,new ,york1 therefore1 is nearly five times larger than the largest balloon ever before built4 ,its form is that of the usual perpendicular gas-receiver1 with basket and lifeboat attached4 ,six thousand yards of twilled cloth have been used in the construction of the envelope4 ,reduced to feet1 the actual measurement of this material is #ed1jjj feet--or nearly #aa miles4 ,seventeen of ,wheeler and ,wilson's sewing machines have been employed to connect the pieces1 and the upper extremity of the envelope1 intended to receive the gas-valve1 is of triple thickness1 strengthened with heavy brown linen1 and sewed in triple seams4 ,the pressure being greatest at this point1 extraordinary power of resistance is requisite4 ,it is asserted that #ajj women1 sewing constantly for two years1 could not have accomplished this work1 which measures by miles4 ,the material is stout and the stitching stouter4 ,the varnish applied to this envelope is a composition the secret of which rests with ,mr4 ,lowe4 ,three or four coatings are applied1 in order to prevent leakage of the gas4 ,the netting which surrounds the envelope is a stout cord1 manufactured from flax expressly for the purpose4 ,its aggregate strength is equal to a resistance of #afj tons1 each cord being capable of sustaining a weight of #djj lbs4 or #ejj lbs4 ,the basket which is to be suspended immediately below the balloon is made of rattan1 is #bj feet in circumference and #d feet deep4 ,its form is circular1 and it is surrounded by canvas4 ,this car will carry the aeronauts4 ,it is warmed by a lime-stove1 an invention of ,mr4 ,o4 ,a4 ,gager1 by whom it was presented to ,mr4 ,lowe4 ,a lime-stove is a new feature in air voyages4 ,it is claimed that it will furnish heat without fire1 and is intended for a warming apparatus only4 ,the stove is #a feet high1 and #b feet square4 ,mr4 ,lowe states that he is so well convinced of the utility of this contrivance1 that he conceives it to be possible to ascend to a region where water will freeze1 and yet keep himself from freezing4 ,this is to be tested4 ,dropping below the basket is a metallic lifeboat1 in which is placed an ,ericsson engine4 ,captain ,ericsson's invention is therefore to be tried in mid-air4 ,its particular purpose is the control of a propeller1 rigged upon the principle of the screw1 by which it is proposed to obtain ,page#aad a regulating power4 ,the application of the mechanical power is ingeniously devised4 ,the propeller is fixed in the bow of the lifeboat1 projecting at an angle of about forty-five degrees4 ,from a wheel at the extremity twenty fans radiate4 ,each of these fans is #e feet in length1 widening gradually from the point of contact with the screw to the extremity1 where the width of each is #a feet4 ,mr4 ,lowe claims that by the application of these mechanical contrivances his air-ship can be readily raised or lowered1 to seek different currents of air2 that they will give him ample steerage way1 and that they will prevent the rotatory motion of the machine4 ,in applying the principle of the fan1 he does not claim any new discovery1 but simply a practical development of the theory advanced by other aeronauts1 and partially reduced to practice by ,charles ,green1 the celebrated ,english aeronaut4 ,mr4 ,lowe contends that the application of machinery to aerial navigation has been long enough a mere theory4 ,he proposes to reduce the theory to practice1 and see what will come of it4 ,it is estimated that the raising and lowering power of the machinery will be equal to a weight of #cjj lbs41 the fans being so adjusted as to admit of very rapid motion upward or downward4 ,as the loss of three or four pounds only is sufficient to enable a balloon to rise rapidly1 and as the escape of a very small portion of the gas suffices to reduce its altitude1 ,mr4 ,lowe regards this systematic regulator as quite sufficient to enable him to control his movements and to keep at any altitude he desires4 ,it is his intention to ascend to a height of three or four miles at the start1 but this altitude will not be permanently sustained4 ,he prefers1 he says1 to keep within a respectable distance of mundane things1 where 'he can see folks4' ,it is to be hoped his machinery will perform all that he anticipates from it4 ,it is a novel affair throughout1 and a variety of new applications remain to be tested4 ,mr4 ,lowe1 expressing the utmost confidence in all the appointments of his apparatus1 assured us that he would certainly go1 and1 as certainly1 would go into the ocean1 or deliver a copy of ,monday's ,times in ,london on the following ,wednesday4 ,he proposes to effect a landing in ,england or ,france1 and will take a course north of east4 ,a due easterly course would land him in ,spain1 but to that course he objects4 ,he hopes to make the trip from this city to ,london in forty-eight hours1 certainly in sixty-four hours4 ,he scouts the idea of danger1 goes about his preparations deliberately1 and promises himself a good time4 ,as the upper currents1 setting due east1 will not permit his return by the same route1 he proposes to pack up the ,city of ,new ,york1 and take the first steamer for home4 ,the air-ship will carry weight4 ,its cubical contents of #gbe1jjj feet of gas suffice to lift a weight of #bb tons4 ,with outfit complete its own weight will be #c tons4 ,with this weight #ai tons of lifting power remain1 and there is accordingly room for as many passengers as will care to take the venture4 ,we understand1 however1 that the company is limited to eight or ten4 ,mr4 ,lowe provides sand for ballast1 regards his chances of salvation as exceedingly favourable1 ,page #aae places implicit faith in the strength of his netting1 the power of his machinery1 and the buoyancy of his lifeboat1 and altogether considers himself secure from the hazard of disaster4 ,if he accomplish his voyage in safety1 he will have done more than any air navigator has yet ventured to undertake4 ,if he fail1 the enterprise sinks the snug sum of #bj1jjj dollars4 ,wealthy men who are his backers1 sharing his own enthusiasm1 declare failure impossible1 and invite a patient public to wait and see4 ,a night ascent witnessed at any of the public gardens is certainly a stirring scene1 particularly if the wind is rather high4 ,on approaching the balloon1 swayed to and fro by the breeze1 it seems almost capable of crushing the bold individual who would venture beneath it2 seen as a large dark mass in the yet dimly-lighted square1 it appears to be incapable of control2 when the inflation is completed1 the aeronaut1 all importance1 seats himself in the car1 and blue lights1 with other fireworks1 display the victim who is to make a last ascent1 or perhaps descent4 ,finally the word is given1 the ropes are cast off1 and the bulky chariot rises majestically to the sound of the ,national ,anthem4 ,the crowd see no more1 but the next day's ,times reports the end of the aerial journey4 ,balloons can never be of any permanent value as means of locomotion until they can be steered2 and this is a problem1 the solution of which is something like perpetual motion4 ,in the first place1 a balloon of any size exposes an enormous surface to the pressure and force of the winds2 and when we consider that they move at the rate of from three to eighty miles per hour1 it will be understood that the fabric of the balloon itself must give way in any attempt to tear1 work1 or pull it against such a force4 ,secondly and lastly1 the power has not yet been created which will do all this without the inconvenience of being so heavy that the steering engine fixes the balloon steadily to the earth by its obstinate gravity4 ,when engines of power are constructed without the aeronaut's obstacle of weight--when balloons are made of thin copper or sheet-iron1 then we may possibly hear of the voyage of the good ship ,aerial1 bound for any place1 and quite independent of dock1 port1 and the host of dues 7quere71 which the sea-going ships have to disburse4 ,it is1 however1 gratifying to the zeal and perseverance of those who dream of aerial navigation1 to know that a balloon is not quite useless2 and here we may return to the consideration of ,mr4 ,darby's signals1 which are of various kinds1 and intended to appeal to the senses by night as well as by day2 and first1 by audible sounds4 ,such means have long been recognised1 from the ancient float and bell of the ,inchcape ,rock1 to the painful minute-gun at sea1 or the shrill railway whistle and detonating signals employed to prevent the horrors of a collision between two trains4 ,the signal sounds are produced by the explosion of shells capable of yielding a report equal to that of a six-pounder cannon1 and they are constructed in a very simple manner4 ,a ball1 composed of wood or copper1 and made up by screwing together the two hemispheres1 is attached to a shaft or tail of cane or lance-wood1 properly feathered like an arrow2 at the side opposite to that of the arrow--viz41 at its antipodes1 is placed a slight protuberance ,page #aaf;containing a minute bulb of glass filled with oil of vitriol1 and surrounded with a mixture of chlorate of potash and sugar1 the whole being protected with gutta-percha1 and communicating by a touch-hole with the interior1 which is of course filled with gunpowder4 ,these shells are attached to a circular framework by a strong whipcord1 which passes to a central fuse1 and are detached one after the other as the slow fuse 7made hollow on the principle of the argand lamp7 burns steadily away4 ,directly a shell falls to the ground1 the little bulb containing the oil of vitriol breaks1 and the acid coming in contact with the chlorate of potash and sugar1 causes the mixture to take fire1 when the gunpowder explodes4 ,during the siege of ,sebastopol many similar mines were prepared by the ,russians in the earth1 so that when an unfortunate soldier trod upon the spot1 the concealed mine blew up and seriously injured him2 such petty warfare is as bad as shooting sentries1 and a cruel application of science1 that unnecessarily increases the miseries of war without producing those grand results for which the truly great captains1 ,wellington and ,napoleon1 only warred4 7,fig4 #aae47 ,illustration3 ,fig4 #aae4 ,a4 ,ring attached to balloon1 carrying an hexagonal framework with six shells4 ,b4 ,hollow fuse1 which burns slowly up to the strings1 and detaches each shell in succession4 ,c4 ,section of shell4 ,the shaded portion represents the gunpowder4 ,illustration3 ,fig4 #aaf4 ,the bill distributor1 consisting of three hollow fuses1 with bills attached in packets4 ,the bill distributor consists of a long piece of wood1 to which are ,page #aag attached a number of hollow fuses1 with packets of bills1 protected from being burned or singed by a thin tin plate2 #aj1jjj or #bj1jjj bills can thus be delivered1 and the wind assists in scattering them1 whilst the balloon travels over a distance of many miles4 ,it must be recollected that in each case the shells and the bills are detached by the string burning away as the fire creeps up from the fuse4 7,fig4 #aaf47 ,another most ingenious arrangement1 also prepared by ,mr4 ,darby1 is termed by the inventor1 the ,land and ,water ,signal1 and may be thus described3--,a short hollow ball of gutta-percha1 or other convenient material1 five or six inches in diameter1 and filled with printed bills1 or the information1 whatever it may be1 that is required to be sent1 is attached to a cap to which a red flag1 having the words ,open the shell and four cross sticks1 canes1 or whalebones with bits of cork at equal distances1 are fitted4 ,the whole is connected by a string to the fuse as before described4 ,these signals are adapted for land and water3 in either case they fall upright1 and in consequence of the sticks projecting out they float well in the water1 and can be seen by a telescope at a distance of three miles4 7,fig4 #aag47 ,many of these signals were sent away by ,mr4 ,darby from ,vauxhall2 one was picked up at ,harwich1 another at ,brighton1 a third at ,croydon2 in the latter case it was found by a cottager1 who1 fearing gunpowder and combustibles1 did not examine the shell1 but having mentioned the circumstance to a gentleman living near him1 they agreed to cut it open2 and intelligence of their arrival1 in this and the other cases1 was politely forwarded to ,mr4 ,darby at ,vauxhall ,gardens4 ,illustration3 ,fig4 #aag4 ,the land and water signal1 which remains upright on land1 or floats on the surface of water4 ,a4 ,the water-tight gutta-percha shell1 containing the message or information4 ,b ,b ,b4 ,sticks of cane to keep the flag in an upright position2 at the ends are attached cork bungs4 ,balloons1 like a great many other clever inventions1 have been despised by military men as new-fangled expedients1 toys1 which may do very well to please the gaping public1 but are and must be useless in the field4 ,over and over again it has been suggested that a balloon corps for observation should be attached to the ,british army1 but the scheme has ,page #aah been rejected1 although the expense of a few yards of silk and the generation of hydrogen gas would be a mere bagatelle as compared with the transport and use of a single #cb-pounder cannon4 ,the antiquated notions of octogenarian generals have1 however1 received a great shock in the fact that the ,emperor ,napoleon ,,iii4 was enabled1 by the assistance of a captive balloon1 to watch the movements and dispositions of the ,austrian troops2 and with the aid of the information so obtained1 he made his preparations1 and was rewarded by the victory of ,solferino2 and as soon as the battle was over ,napoleon ,,iii4 occupied at ,cavriana the very room and ate the dinner prepared for his adversary1 the ,emperor ,francis ,joseph4 ,over and over again the most excellent histories have been written of aerostation1 but they all tend to one truth1 and that is1 the great danger and risk of such excursions2 and to enable our readers to form their own judgment1 a chronological list of some of the most celebrated aeronauts1 c41 is appended4 #afge4 ,bernair attempted to fly--killed4 #afgh4 ,besnier attempted to fly4 #aggb4 ,l',abb ,desforges announced an aerial chariot4 #aghc4 ,montgolfier constructed the first air balloon4 ,roberts frres1 first gas balloon1 destroyed by the peasantry of ,geneva1 who imagined it to be an evil spirit or the moon4 #aghd4 ,madame ,thibl1 the first lady who was ever up in the clouds2 she ascended #ac1ejj feet4 ,duke de ,chartres1 afterwards ,egalit ,orleans1 travelled #ace miles in five hours in a balloon4 ,testu de ,brissy1 equestrian ascent4 ,d',achille1 ,desgranges1 and ,chalfour--,montgolfier balloon4 ,bacqueville attempted a flight with wings4 ,lunardi--gas balloon4 ,rambaud--,montgolfier balloon1 which was burnt4 ,andreani--,montgolfier balloon4 #aghe4 ,general ,money--gas balloon1 fell into the water1 and not rescued for six hours4 ,thompson1 in crossing the ,irish ,channel1 was run into with the bowsprit of a ship whilst going at the rate of twenty miles per hour4 ,brioschi--gas balloon ascended too high and burst the balloon2 the hurt he received ultimately caused his death4 ,a ,venetian nobleman and his wife--gas balloon--killed4 ,pilatre de ,rozier and ,m4 ,romain--gas balloon took fire--both killed4 #ahjf4 ,mosment--gas balloon--killed4 ,olivari--,montgolfier balloon--killed4 #ahjh4 ,degher attempted a flight with wings4 #ahab4 ,bittorf--,montgolfier balloon--killed4 #ahai4 ,blanchard1 ,madame--gas balloon--killed4 ,page #aai #ahai4 ,gay ,lussac--gas balloon1 ascended #bc1jdj feet above the level of the sea4 ,barometer #ab4ie inches2 thermometer #ad4i ,fah4 ,gay ,lussac and ,biot--gas balloon for the benefit of science4 ,both philosophers returned safely to the earth4 #ahbd4 ,sadler--gas balloon--killed4 ,sheldon--gas balloon4 ,harris--gas balloon--killed4 #ahcf4 ,cocking--parachute from gas balloon--killed4 #ahdg4 ,godard--,montgolfier balloon fell into and extricated from the ,seine4 #ahej4 ,poitevin1 a successful ,french aeronaut4 ,gale1 ,lieut4--gas balloon--killed4 ,bixio and ,barral--gas balloon4 ,graham1 ,mr4 and ,mrs4--gas balloon4--,serious accident ascending near the ,great ,exhibition in ,hyde ,park4 ,green1 the most successful living aeronaut of the present time4 ,of the #da persons enumerated1 #ad were killed1 and nearly all the aeronauts met with accidents which might have proved fatal4 ,illustration3 ,fig4 #aah4 ,flying machine 7theoretical74 ,page #abj ,tenth ,experiment4 ,soap bubbles blown with hydrogen gas ascend with great rapidity1 and break against the ceiling2 if interrupted in their course with a lighted taper they burn with a slight yellow colour and dull report4 ,eleventh ,experiment4 ,by constructing a pewter mould in two halves1 of the shape of a tolerably large flask1 a balloon of collodion may be made by pouring the collodion inside the pewter vessel1 and taking care that every part is properly covered2 the pewter mould may be warmed by the external application of hot water1 so as to drive off the ether of the collodion1 and when quite dry the mould is opened and the balloon taken out4 ,such balloons may be made and inflated with hydrogen by attaching to them a strip of paper1 dipped in a solution of wax and phosphorus1 and sulphuret of carbon2 as the latter evaporates1 the phosphorus takes fire and spreads to the balloon2 which burns with a slight report4 ,the pewter mould must be very perfectly made1 and should be bright inside2 and if the balloons are filled with oxygen and hydrogen1 allowing a sufficient excess of the latter to give an ascending power1 they explode with a loud noise directly the fire reaches the mixed gases4 ,twelfth ,experiment4 ,in a soup-plate place some strong soap and water2 then blow out a number of bubbles with a mixture of oxygen and hydrogen2 a loud report occurs on the application of flame1 and if the room is small the window should be placed open1 as the concussion of the air is likely to break the glass4 ,thirteenth ,experiment4 ,any noise repeated at least thirty-two times in a second produces a musical sound1 and by producing a number of small explosions of hydrogen gas inside glass tubes of various sizes1 the most peculiar sounds are obtained4 ,the hydrogen flame should be extremely small1 and the glass tubes held over it may be of all lengths and diameters2 a trial only will determine whether they are fit for the purpose or not4 ,fourteenth ,experiment4 ,flowers1 figures1 or other designs1 may be drawn upon silk with a solution of nitrate of silver1 and the whole being moistened with water1 is exposed to the action of hydrogen gas1 which removes the oxygen from the silver1 and reduces it to the metallic state4 ,in like manner designs drawn with a solution of chloride of gold are produced in the metallic state by exposure to the action of hydrogen gas4 ,chloride of tin1 usually termed muriate of tin1 may also be reduced in a similar manner1 care being taken in these experiments that ,page #aba the fabric upon which the letters1 figures1 or designs are painted with the metallic solution be kept quite damp whilst exposed to the hydrogen gas4 ,fifteenth ,experiment4 ,a mixture of two volumes of hydrogen with one volume of oxygen explodes with great violence1 and produces two volumes of steam1 which condense against the sides of the strong glass vessel1 in which the experiment may be made1 in the form of water4 ,as the apparatus called the ,cavendish bottle1 by which this experiment only may be safely performed1 is somewhat expensive1 and requires the use of an air-pump1 gas jars with stop-cocks1 and an electrical machine and ,leyden jar1 other and more simple means may be adopted to show the combination of oxygen and hydrogen1 and formation of water4 ,if a little alcohol is placed in a cup and set on fire1 whilst an empty cold gas jar is held over the flame1 an abundant deposition of moisture takes place from the combustion of the hydrogen of the spirits of wine4 ,alcohol contains six combining properties of hydrogen1 with four of charcoal and two of oxygen4 ,if a lighted candle1 or an oil1 camphine1 ,belmontine1 or gas flame1 is placed under a proper condenser1 large quantities of water are obtained by the combustion of these substances4 7,fig4 #aai47 ,illustration3 ,fig4 #aai4 ,a4 ,a burning candle1 or oil or gas lamp4 ,copper head and long pipe fitting into ,b ,c1 the receiver from which the condensed water drops into ,d4 ,e ,e4 ,two corks fitted1 between which is folded some wet rag4 ,page #abb ,sixteenth ,experiment4 ,during the combustion of a mixture of two volumes of hydrogen with one of oxygen1 an enormous amount of heat is produced1 which is usefully applied in the arrangement of the oxy-hydrogen blowpipe4 ,the flame of the mixed gases produces little or no light1 but when directed on various metals contained in a small hole made in a fire brick1 a most intense light is obtained from the combustion of the metals1 which is variously coloured1 according to the nature of the substances employed4 ,with cast-iron the most vivid scintillations are obtained1 particularly if after having fused and boiled the cast-iron with the jet of the two gases1 one of them1 viz41 the hydrogen1 is turned off1 and the oxygen only directed upon the fused ball of iron1 then the carbon of the iron burns with great rapidity1 the little globule is enveloped in a shower of sparks1 and the whole affords an excellent notion of the principle of ,bessemer's patent method of converting cast-iron at once into pure malleable iron1 or by stopping short of the full combustion of carbon1 into cast-steel4 ,the apparatus for conducting these experiments is of various kinds1 and different jets have been from time to time recommended on account of their alleged safety4 ,it may be asserted that all arrangements proposed for burning any quantity of the mixed gases are extremely dangerous3 if an explosion takes place it is almost as destructive as gunpowder1 and should no particular damage be done to the room1 there is still the risk of the sudden vibration of the air producing permanent deafness4 ,if it is desired to burn the mixed gases1 perhaps the safest apparatus is that of ,gurney2 in this arrangement the mixed gases bubble up through a little reservoir of water1 and thus the gas-holder--viz41 a bladder1 is cut off from the jet when the combustion takes place4 7,fig4 #abj47 ,this jet is much recommended by ,mr4 ,woodward1 the highly respected ,president of the ,islington ,literary and ,scientific ,institution1 and may be fitted up to show the phenomena of polarized light1 the microscope1 and other interesting optical phenomena4 ,illustration3 ,fig4 #abj4 ,gurney's jet4 ,a4 ,pipe with stop-cock leading from the gas-holder4 ,b4 ,the little reservoir of water through which the mixed gases bubble4 ,c4 ,the jet where the gases burn4 ,d4 ,cork1 which is blown out if the flame recedes in the pipe1 ,c4 ,mr4 ,woodward states1 that a series of experiments1 continued during many years1 has proved1 that while the bladder containing the mixed gases is under pressure1 the flame cannot be made to pass the safety chambers1 and consequently an explosion is impossible2 and even if through extreme carelessness or design1 as by the removal of pressure or the contact of a spark with the bladder1 an explosion occurs1 it can produce no other than the momentary effect of the alarm occasioned by the report2 ,page #abc whereas1 when the gases are used in separate bags under a pressure of two or three half hundredweights1 if the pressure on one of the bags be accidentally removed or suspended1 the gas from the other will be forced into it1 and if not discovered in time1 will occasion an explosion of a very dangerous character2 or if through carelessness one of the partially emptied bags should be filled up with the wrong gas1 effects of an equally perilous nature would ensue4 ,illustration3 ,fig4 #aba4 ,a4 ,the bladder of mixed gases1 pressed by the board1 ,b ,b1 attached by wire supports to another board1 ,c ,c1 which carries the weights1 ,d ,d4 ,e ,e4 ,pipe to which the bladder1 ,a1 is screwed1 and when ,a is emptied1 it is re-filled from the other bladder1 ,r4 ,f ,f ,f4 ,pipe conveying mixed gases to the lantern1 ,g ,g1 where they are burnt from a ,gurney's jet1 ,h4 ,in the oxy-hydrogen blowpipe usually employed1 the gases are kept quite separate1 either in gasometers or gas bags1 and are conveyed by distinct pipes to a jet of very simple construction1 devised by the late ,professor ,daniell1 where they mix in very small volumes1 and are burnt at once at the mouth of the jet4 7,fig4 #abb47 ,illustration3 ,fig4 #abb4 ,daniell's jet4 ,o ,o4 ,the stop-cock and pipe conveying oxygen1 and fitting inside the larger tube ,h ,h1 to which is attached a stop-cock1 ,h1 connected with the hydrogen receiver4 ,a4 ,the orifice near which the gases mix1 and where they are burnt4 ,the gases are stored either in copper gasometers or in air-tight bags of ,macintosh cloth1 capable of containing from four to six cubic feet of gas1 and provided with pressure boards4 ,the boards are loaded with two or three fifty-six pound weights to force out the gas with sufficient ,page #d pressure1 and of course must be equally weighted2 if any change of weight is made1 the stop-cocks should be turned off and the light put out1 as the most disastrous results have occurred from carelessness in this respect4 7,fig4 #abc47 ,illustration3 ,fig4 #abc4 ,gas bag and pressure boards4 ,the oxy-hydrogen jet is further varied in construction by receiving the gases from separate reservoirs1 and allowing them to mix in the upper part of the jet1 which is provided with a safety tube filled with circular pieces of wire gauze4 7,fig4 #abd47 ,with this arrangement a most intense light is produced1 called the ,drummond or lime light1 and coal gas is now usually substituted for hydrogen4 ,illustration3 ,fig4 #abd4 ,a ,a4 ,board to which ,b ,b is fixed4 ,o4 ,oxygen pipe4 ,h4 ,hydrogen pipe4 ,c ,c4 ,space filled with wire gauze4 ,d4 ,lime cylinder4 ,page #abe ,seventeenth ,experiment4 ,there are many circumstances that will cause the union of oxygen and hydrogen1 which1 if confined by themselves in a glass vessel1 may be preserved for any length of time without change2 but if some powdered glass1 or any other finely-divided substance with sharp points1 is introduced into the mixed gases at a temperature not exceeding #ffj ,fahrenheit1 then the gases silently unite and form water4 ,this curious mode of effecting their combination is shown in a still more interesting manner by perfectly clear platinum foil1 which if introduced into the mixed gases gradually begins to glow1 and becoming red-hot causes the gases to explode4 ,or still better1 by the method first devised by ,dobereiner1 in #ahbd1 by which finely prepared spongy platinum--i4e41 platinum in a porous state1 and exposing a large metallic surface--is almost instantaneously heated red-hot by contact with the mixed gases4 ,when this fact became known1 it was further applied to the construction of an instantaneous light1 in which hydrogen was made to play upon a little ball of spongy platinum1 and immediately kindled4 ,these ,dobereiner lamps were possessed by a few of the curious1 and would no doubt be extensively used if the discovery of phosphorus had not supplied a cheaper and more convenient fire-giving agent4 ,when the spongy platinum is mixed with some fine pipeclay1 and made into little pills1 they may 7after being slightly warmed7 be introduced into a mixture of the two gases1 and will silently effect their union4 ,the theory of the combination is somewhat obscure1 and perhaps the simplest one is that which supposes the platinum sponge to act as a conductor of electric influences between the two sets of gaseous particles2 although1 again1 it is difficult to reconcile this theory with the fact that powdered glass at #ffj1 a bad conductor of electricity1 should effect the same object4 ,the result appears to be due to some effects of surface by which the gases seem to be condensed and brought into a condition that enables them to abandon their gaseous state and assume that of water4 ,when ,sir ,h4 ,davy invented the safety-lamp1 he was aware that1 in certain explosive conditions of the air in coal mines1 the flame of the lamp was extinguished1 and in order that the miner should not be left in the dreary darkness and intricacies of the galleries without some means of seeing the way out1 he devised an ingenious arrangement with thin platinum wire1 which was coiled round the flame of the lamp1 and fixed properly1 so that it could not be moved from its proper place by any accidental shaking4 ,when the flame of the safety-lamp1 having the platinum wire attached1 was accidentally extinguished by the explosive atmosphere in which it was burning1 the platinum commenced glowing with an intense heat1 and continued to emit light as long as it remained in the dangerous part of the mine4 ,sir ,h4 ,davy warned those who might use the platinum to take care that no portion of the thin wire passed outside the wire gauze1 for the obvious reason that1 if ignited outside the wire gauze protector1 it would inflame the fire-damp4 ,illustration3 ,fig4 #abe4 ,p ,p4 ,two platinum plates connected with wires to the cups4 ,the wires are passed through holes in the finger-glass1 ,b ,b1 and are fixed perfectly steady by pouring in cement composed of resin and tallow to the line ,l ,l4 ,two glass tubes filled with water acidulated with sulphuric acid1 and placed over the platinum plates in finger-glass1 which also contains dilute sulphuric acid to improve the conducting power of the water4 ,the wires of the battery are placed in the cups1 and the arrows show the direction of the current of electricity4 ,page #abf ,eighteenth ,experiment4 ,water is decomposed by passing a current of voltaic electricity through it by means of two platinum plates1 which may be connected with a ten-cell ,grove's battery4 ,the gases are collected in separate tubes1 and the experiment offers one of the most instructive illustrations of the composition of water4 7,fig4 #abe47 ,there is a current of electricity passing from and between two platinum plates decomposing water1 offering the converse of the ,dobereiner experiment1 and highly suggestive of the probability of the theory already advanced in explanation of the singular combination of oxygen and hydrogen in the presence of clean platinum foil1 and more especially when we consider the operation of ,grove's gas battery1 in which a current of electricity is produced by pieces of platinum foil covered with finely-divided platinum1 called platinum black2 each piece is contained in a separate glass tube filled alternately with oxygen and hydrogen1 and by connecting a great number of these tubes a current of electricity is obtained1 whilst the oxygen and hydrogen are slowly absorbed and disappear1 having combined and formed water1 although placed in separate glass tubes4 7,fig4 #abf47 ,the analysis of water is shown very perfectly on the screen by fitting up some very small tubes and platinum wires in the same manner as shown in fig4 #abe4 ,the vessel in which the tubes and wires are contained with the dilute sulphuric acid must be small1 and arranged so as to pass nicely into the space usually filled by the picture in an ordinary magic lantern1 or1 still better1 in one lighted by the oxy-hydrogen or lime light4 ,if the dilute acid is coloured with a little solution of indigo1 the gradual displacement of the fluid by the production of the two gases is very perfectly developed on the screen when the small voltaic battery is attached to the apparatus2 and of course a large number of persons may watch the experiment at the same time4 ,with respect to the application of the light produced from a jet of the ,page #abg mixed gases thrown upon a ball of lime1 it may be stated that for many years the dissolving view lanterns and other optical effects have been produced with the assistance of this light2 and more lately ,major ,fitzmaurice has condensed the mixed gases in the old-fashioned oil gas receivers1 and projected them on a ball of lime2 and it was this light thrown from many similar arrangements that illuminated the ,british men-of-war when ,napoleon ,,iii4 left her ,majesty's yacht at night in the docks at ,cherbourg4 ,illustration3 ,fig4 #abf4 ,grove's gas battery consists of tubes containing oxygen and hydrogen alternately1 and having a thin piece of platinum foil1 ,p1 inserted by the blowpipe in each glass tube4 ,the foil hangs down the full length of the interior of the glass4 ,each pair of tubes is contained in a little glass tumbler containing some dilute sulphuric acid1 and the hydrogen tube1 ,h1 of one pair1 is connected with the oxygen tube1 ,o1 of the next4 ,w ,w4 ,the terminal wires of the series4 ,mr4 ,sykes ,ward1 of ,leeds1 has also proposed a most simple and excellent application of the oxy-hydrogen light for illumination under the ,page #abh surface of water1 and for the convenience of divers1 who are frequently obliged to cease their operations in consequence of the want of light4 ,mr4 ,ward's submarine lamp consists of a series of very strong copper tubes1 which are filled with the mixed gases by means of a force-pump2 and in order to prevent the lamp being extinguished1 it burns under double glass shades1 which are desirable in order to prevent the glass immediately next to the light cracking by contact with the cold water4 ,illustration3 ,fig4 #abg4 ,cherbourg4 ,the author tried this lamp at ,ryde1 and although the coast-guards objected to the production of a brilliant light at night1 which they stated might be mistaken for a signal and would cause some confusion amongst the war vessels in the immediate neighbourhood1 enough experiments were made1 to show that the ,ward lamp would burn for a considerable time under water1 and could be kept charged with the gas by means of a process that was easily workable in the boat4 ,the gases were taken out mixed in gas bags1 and pumped into the reservoir when required4 ,with a much larger reservoir greater results could be obtained2 and if nautilus diving bells are to be used in modern warfare1 they will require a powerful light to show them their prey1 so that they may attach the explosives which are to blow great holes in the men-of-war4 ,illustration3 ,fig4 #abh4 ,a ,a4 ,tube reservoir to hold the mixed gases4 ,b4 ,the jet and lime ball4 ,d4 ,the first glass shade1 held down by a cap and screw4 ,c4 ,the second glass shade4 ,e ,e4 ,the handle by which it is lowered into the water4 ,illustration3 ,fig4 #abi4 ,submarine lamp4 ,page #abi ,,chapter ,,xi4 ,,chlorine1 ,,iodine1 ,,bromine1 ,,fluorine4 ,the four ,halogens1 or ,producers of ,substances like ,sea ,salt4 ,chlorine 7,greek3 chlros1 green74 ,symbol1 ,cl4 ,combining proportion1 #ce4e4 ,specific gravity1 #b4dd4 ,scheele termed it dephlogisticated muriatic acid2 ,lavoisier1 oxymuriatic acid2 ,davy1 chlorine4 ,the consideration of the nature of this important element introduces to our notice one of the most original chemists of the eighteenth century--viz41 the illustrious ,scheele1 who was born at ,stralsund1 in #agdb1 and in spite of every obstacle1 fighting his battle of life with sickness and sorrow1 he succeeded in making some of the most valuable discoveries in science1 and amongst them that of chlorine gas4 ,it was in the examination of a mineral solid--viz41 of manganese--that ,scheele made the acquaintance of a new gaseous element2 and in a highly original dissertation on manganese1 in #aggd1 he describes the mode of procuring what he termed dephlogisticated muriatic acid--a name which is certainly to be regretted1 from its absurd length1 but a title which was strictly in accordance with the then established theory of phlogiston2 and if the latter is considered synonymous with hydrogen1 quite in accordance with our present views of the nature of this element4 ,scheele discovered the leading characteristics of chlorine1 and especially its power of bleaching1 which is alone sufficient to place this gas in a high commercial position1 when it is considered that all our linen used formerly to be sent to ,holland1 where they had acquired great dexterity in the ancient mode of bleaching--viz41 by exposure of the fabric to atmospheric air or the action of the damps or dews1 assisted greatly by the agency of light4 ,some idea may be formed of the present value of chlorine1 when it is stated that the linen goods were retained by the ,dutch bleachers for nine months2 and if the spring and summer happened to be favourable1 the operation was well conducted2 on the other hand1 if cold and wet1 the goods might be more or less injured by continual exposure to unfavourable atmospheric changes4 ,at the present time1 as much bleaching can be done in nine weeks as might formerly have been conducted in the same number of months2 and the whole of the process of chlorine bleaching is carried on independent of external atmospheric caprices1 whilst the money paid for the process no longer passes to ,holland1 but remains in the hands of our own diligent bleachers and manufacturers4 ,first ,experiment4 ,illustration3 ,fig4 #acj4 ,a4 ,flask containing the fuming hydrochloric acid1 which is gently boiled by the heat of the spirit lamp4 ,b4 ,tube passing to the ,wolfe's bottle1 containing pumice-stone or asbestos moistened with sulphuric acid4 ,c4 ,second tube passing into a dry empty bottle1 which receives the hydrochloric acid gas4 ,as ,scheele first indicated1 chlorine is obtained by the action of the black oxide of manganese1 on the ,spirit of ,salt1 or hydrochloric acid2 and the most elementary and instructive experiment showing its preparation can be made in the following manner3-- ,page #acj ,place in a clear ,florence oil-flask1 to which a cork and bent tube have been first fitted1 some strong fuming hydrochloric acid4 ,arrange the flask on a ring-stand1 and then pass the bent tube either to a ,wolfe's bottle containing some pumice-stone moistened with oil of vitriol1 or to a glass tube containing either pumice or asbestos wetted with the same acid4 ,another glass tube1 bent at right angles1 passes away from the ,wolfe's bottle into a receiving bottle4 7,fig4 #acj74 ,on the application of heat1 the hydrochloric gas is driven off from its solution in water1 and any aqueous vapour carried up is retained by the asbestos or pumice stone wetted with oil of vitriol2 the application of the latter is called drying the gas--i4e41 depriving it of all moisture2 sometimes the salt called chloride of calcium is used for the same purpose1 and it must be understood by the juvenile chemist that gases are not dried like towels1 by exposure to heat1 or by putting them in bladders before the fire1 as we once heard was actually recommended1 but by causing the gas charged with invisible steam to pass over some substance having a great affinity for water4 ,the dry hydrochloric gas falls into the bottle1 and displaces the air1 being about one-fourth heavier than the latter1 and gradually overflowing from the mouth of the vessel1 produces a white smoke1 which is found to be acid by litmus paper1 but has no power to bleach1 and is not green2 it is1 in fact1 a combination of one combining proportion of chlorine with one of hydrogen1 and to detach the latter1 and set the chlorine free1 it is necessary to convey the hydrochloric gas to some body which has an affinity for hydrogen4 ,such a substance is provided in the use of the black oxide of manganese1 which is placed either in a small flask or in a tube provided with two bulbs1 and when heated with the lamp it separates the hydrogen from the hydrochloric gas1 and forms water1 which partly condenses in the second bulb4 ,and now the gas that escapes is no longer acid and fuming with a white smoke on contact with the air2 but is green1 has a strong odour1 bleaches1 and is so powerful in its action on all living tissues1 that it must be carefully avoided and not inhaled2 if a small quantity is accidentally inhaled1 it produces a violent fit of coughing1 which lasts a ,page #aca considerable time1 and is only abated by inhaling the diluted vapour of ammonia1 or ether1 or alcohol1 and swallowing milk and other softening drinks4 7,fig4 #aca47 ,illustration3 ,fig4 #aca4 ,a4 ,the flask containing the fuming hydrochloric acid1 heated by spirit lamp4 ,b4 ,tube passing to ,wolfe's bottle1 containing the pumice-stone or asbestos wetted with oil of vitriol4 ,c4 ,second tube1 which passes into a wide-mouthed small flask containing black oxide of manganese1 partly in powder and partly in lump2 and the third tube conveys the chlorine to any convenient vessel4 ,the double bulb tube1 ,e ,e1 may be substituted for the flask1 the oxide of manganese being contained in the bulb ,m4--,n4,b4 ,any tube may be joined on to another by a bit of india-rubber tubing1 which is tied by string4 ,illustration3 ,tube ,a is joined to tube ,b by the caoutchouc pipe ,c1 tied with packthread4 ,second ,experiment4 ,the mode of preparing chlorine1 as already given1 though very instructive1 is troublesome to perform2 a more simple process may therefore be described3-- ,pour some strong hydrochloric acid upon powdered black oxide of manganese contained in a ,florence oil-flask1 taking care that the whole of the black powder is wetted with the acid so that none of it clings to the bottom of the flask in the dry state to cause the glass to crack on the application of heat4 ,a cork and bent glass tube is now attached1 and conveyed to the pneumatic trough2 on the application of heat to the mixture in the flask the chlorine is evolved1 and may be collected in stoppered bottles1 the first portion that escapes1 although it contains atmospheric air1 should be carefully collected in order to prevent any ,page #acb accident from inhaling the gas1 and it will do very well to illustrate the bleaching power of the gas1 and therefore need not be wasted4 ,the above process may be described in symbols1 all of which are easily deciphered by reference to the table of elements1 page #hf4 ,mn,o#b #b ,h,cl ,mn,cl #b;,,ho ,cl4 ,third ,experiment4 ,another and still more expeditious mode of preparing a little chlorine1 is by placing a small beaker glass1 containing half an ounce of chlorinated lime1 usually termed chloride of lime or bleaching powder1 carefully at the bottom of a deep and large beaker glass1 and then1 by means of a tube and funnel1 conveying to the chloride of lime some dilute oil of vitriol1 composed of half acid and half water2 effervescence immediately occurs from the escape of chlorine gas1 and as it is produced it falls over the sides of the small beaker glass into the large one1 when it may be distinguished by its green colour4 ,if a little gas be dipped out with a very small beaker glass arranged as a bucket1 and poured into a cylindrical glass containing some dilute solution of indigo1 and shaken therewith1 the colour disappears almost instantaneously2 and if a piece of ,dutch metal is thrown into the beaker glass it will take fire if enough chlorine has been generated1 or some very finely-powdered antimony will demonstrate the same result4 ,thus1 with a few beaker glasses1 some chloride of lime1 sulphuric acid1 a solution of indigo1 and a little ,dutch metal1 the chief properties of chlorine may be displayed4 7,fig4 #acb47 ,illustration3 ,fig4 #acb4 ,a ,a4 ,the large beaker glass4 ,b4 ,the small one1 containing the chloride of lime4 ,c4 ,the tube and funnel down which the dilute sulphuric acid is poured4 ,d ,d4 ,sheet of paper over top of large glass1 with hole in centre to admit the tube4 ,e4 ,the little beaker used as a bucket4 ,fourth ,experiment4 ,into a little platinum spoon place a small pellet of the metal sodium1 and after heating it in the flame of a spirit lamp1 introduce the metal ,page #acc into a bottle of chlorine1 when a most intense and brilliant combustion occurs1 throwing out a vivid yellow light1 and the heat is frequently so great that the bottle is cracked4 ,after the combustion1 and when the bottle is cool1 it is usually lined with a white powder1 which will be found to taste exactly the same as salt1 and1 in fact1 is that substance1 produced by the combination of chlorine1 a virulent poison1 with the metal sodium1 which takes fire on contact with a small quantity of water2 and hence the use of salt for the preparation of chlorine gas when it is required on the large scale4 ,parts4 ,common salt #d ,black oxide of manganese #a ,sulphuric acid #b ,water #b ,fifth ,experiment4 ,some ,dutch metal1 or powdered antimony1 or a bit of phosphorus1 immediately takes fire when introduced into a bottle containing chlorine gas1 forming a series of compounds termed chlorides1 and demonstrating by the evolution of heat and light1 the energetic character of chlorine1 and that oxygen is not the only supporter of combustion2 chlorine gas has even1 in some cases1 greater chemical power1 because some time elapses before phosphorus will ignite in oxygen gas1 whilst it takes fire directly when placed in a bottle of chlorine4 ,sixth ,experiment4 ,the weight and bleaching power of chlorine are well shown by placing a solution of indigo in a tall cylindrical glass1 leaving a space at the top of about five inches in depth4 ,by inverting a bottle of chlorine over the mouth of the cylindrical glass1 it pours out like water1 being about two and a half times heavier than atmospheric air1 and then1 after placing a ground glass plate over the top of the glass1 the chlorine is recognised by its colour1 whilst the bleaching power is demonstrated immediately the gas is shaken with the indigo solution4 ,seventh ,experiment4 ,as a good contrast to the last experiment1 another cylindrical jar of the same size may be provided1 containing a solution of iodide of potassium with some starch1 obtained by boiling a teaspoonful of arrowroot with some water2 any chlorine left in the bottle 7sixth experiment7 may be inverted into the top of this glass and shaken1 when it turns a beautiful purple blue in consequence of the liberation of iodine by the chlorine1 whose greater affinity for the base produces this result4 ,the colour is caused by the union of the iodine and the starch1 which form together a beautiful purple compound1 and thus the apparent anomaly of destroying and producing colour with the same agent is explained4 ,page #acd ,eighth ,experiment4 ,dry chlorine does not bleach1 and this fact is easily proved by taking a perfectly dry bottle1 and putting into it two or three ounces of fused chloride of calcium broken in small lumps1 then if a bottle full of chlorine is inverted over the one containing the chloride of calcium1 taking the precaution to arrange a few folds of blotting paper with a hole in the centre on the top of the latter to catch any water that may run out of the chlorine bottle at the moment it is inverted1 the gas will be dried by contact with the chloride of calcium1 and if a piece of paper1 with the word chlorine written on it with indigo1 and previously made hot and dry1 is placed in the chlorine1 no change occurs1 but directly the paper is removed1 dipped in water1 and placed in a bottle of damp chlorine1 the colour immediately disappears4 7,fig4 #acc47 ,illustration3 ,fig4 #acc4 ,a ,a4 ,dry bottle1 containing chloride of calcium4 ,b4 ,bottle of chlorine4 ,the arrow indicates the gas4 ,c ,c4 ,the blotting-paper1 to catch any water from the bottle1 ,b4 ,d4 ,the bottle closed1 and containing the paper4 ,this experiment shows that chlorine is only the means to the end1 and that it decomposes water1 setting free oxygen1 which is supposed to exert a high bleaching power in its nascent state1 a condition which many gases are imagined to assume just before they take the gaseous state1 a sort of intermediate link between the solid or fluid and the gaseous condition of matter4 ,the nascent state may possibly be that of ozone1 to which we have already alluded as a powerful bleaching agent4 ,ninth ,experiment4 ,a piece of paper dipped in oil of turpentine emits a dense black smoke1 and frequently a flash of fire is perceptible1 directly it is plunged into a bottle containing chlorine gas2 here the gas combines only with the hydrogen of the turpentine1 and the carbon is deposited as soot4 ,tenth ,experiment4 ,if a lighted taper is plunged into a bottle of chlorine it continues to burn1 emitting an enormous quantity of smoke1 for the reason already explained1 and demonstrating the perfection of the atmosphere in which ,page #ace we live and breathe1 and showing that had oxygen gas possessed the same properties as chlorine1 the combustion of compounds of hydrogen and carbon would have been impossible1 in consequence of the enormous quantity of soot which would have been produced1 so that some other element that would freely enter into combination with it must have been provided to produce both artificial light and heat4 ,chlorine is a gas which cannot be inhaled1 and ozone presents the same features1 as a mouse confined for a short time with an excess of ozone soon died2 but ozone is the extraordinary condition of oxygen2 the element in the ordinary state is harmless1 and is the one which enters so largely into the composition of the air we breathe4 ,eleventh ,experiment4 ,when one volume of olefiant gas 7prepared by boiling one measure of alcohol and three of sulphuric acid7 is mixed with two volumes of chlorine1 and the two gases agitated together in a long glass vessel for a few seconds1 with a glass plate over the top1 which should have a welt ground perfectly flat1 they unite on the application of flame1 with the production of a great cloud of black smoke1 arising from the deposited carbon1 whilst a sort of roaring noise is heard during the time that the flame passes from the top to the foot of the glass4 7,fig4 #acd47 ,illustration3 ,fig4 #acd4 ,remarkable deposition of carbon during the combustion of one volume of olefiant gas with two of chlorine4 ,twelfth ,experiment4 ,formerly ,bandannah handkerchiefs were in the highest estimation1 and no gentleman's toilet was thought complete without one4 ,the pattern was of the simplest kind1 consisting only of white spots on a red or other coloured ground4 ,these spots were produced in a very ingenious manner by ,messrs4 ,monteith1 of ,glasgow1 by pressing together many layers of silk with leaden plates perforated with holes2 a solution of chlorine was then poured upon the upper plate1 and pressure being applied it penetrated the whole mass in the direction of the holes1 bleaching out the colour in its passage4 ,this important commercial result may be imitated on the small scale by placing a piece of calico dyed with ,turkey red between two thick pieces of board1 each of which is ,page #acf perforated with a hole two inches in diameter1 and corresponding accurately when one is placed upon the other4 ,the pieces of board may be squeezed together in any convenient way1 either by weights1 strong vulcanized india-rubber bands or screws1 and when a strong solution of chlorine gas or of chloride of lime is poured into the hole and percolates through the cloth1 the colour is removed1 and the part is bleached almost instantaneously by first wetting the calico with a little weak acid1 and then pouring on the solution of chloride of lime4 ,on removing and washing the folded red calico it is found to be bleached in all the places exposed to the solution1 and is now covered with white spots4 7,fig4 #ace47 ,illustration3 ,fig4 #ace4 ,a4 ,circular hole in the upper piece of wood1 a similar one being perforated in the lower one4 ,b ,b4 ,the strong india-rubber bands4 ,the bleaching solution is poured into ,a4 ,,iodine4 ,iodine 7,greek3 ,ids1 violet coloured74 ,symbol1 ,i2 combining proportion1 #abg4a2 specific gravity1 #d4idh4 ,specific gravity of iodine vapour1 #h4gaf4 ,in the previous chapter1 devoted to the element chlorine1 little or nothing has been said of that inexhaustible storehouse of chlorine1 iodine1 and bromine--viz41 the boundless ocean4 ,some one has remarked that1 as it is possible the air may contain a little of everything capable of assuming the gaseous form1 so the ocean may hold in a state of solution a modicum of every soluble substance1 in proof of which we have lately read of some very important experiments resulting in the separation of the metal silver from sea water1 not certainly in any profitable quantity1 but quite enough to prove its presence in the ocean4 ,no elaborate research is necessary to ascertain the presence of chlorine1 when it is remembered that ,schafhutl has calculated1 that all the oceans on the globe contain three millions fifty-one thousand three hundred and forty-two cubic geographical miles of salt1 or about five times more than the mass of the ,alps4 ,now1 salt contains about #fj per cent4 of chlorine gas1 and therefore the bleachers can never stand still for want of it2 but iodine is not so plentiful1 and was discovered by ,m4 ,courtois1 of ,paris1 in kelp1 a substance from which he prepared carbonate of soda1 or washing soda2 but as this is now more cheaply prepared from common salt1 the kelp is at present required only for the iodine salts it contains1 as also for the chloride of potassium4 ,kelp is obtained by burning dried sea-weeds in a ,page #acg shallow pit2 the ashes accumulate and melt together1 and this fused mass broken into lumps forms kelp4 ,the ocean bed no doubt has its fertile and barren plains and mountains1 and amongst the so-called oceanic meadows are to be mentioned the two immense groups and bands of sea-weed called the ,sargasso ,sea1 which occupy altogether a space exceeding six or seven times the area of ,germany4 ,the iodine is contained in the largest proportion in the deep sea plants1 such as the long elastic stems of the fucus palmatus1 c4 ,the kelp is lixiviated with water1 and after separating all the crystallizable salts1 there remains behind a dense oily-looking fluid1 called iodine ley1 to which sulphuric acid is added1 and after standing a day or two the acid ley is placed in a large leaden retort1 and heated gently with black oxide of manganese4 ,the chlorine being produced very slowly1 liberates the iodine1 as already demonstrated in experiment seven1 p4 #acc1 and it is collected in glass receivers4 ,iodine1 when quite pure and well crystallized1 has a most beautiful metallic lustre1 and presents a bluish-black colour1 affording an odour which reminds one at once of the sea smell4 ,first ,experiment4 ,a few grains of iodine placed in a flask may be sublimed at a very gentle heat1 and afford a magnificent violet vapour1 which can be poured out of the flask into a warm bottle4 ,if the bottle is cold the iodine condenses in minute and brilliant crystals4 7,fig4 #acf47 ,illustration3 ,fig4 #acf4 ,a4 ,flask containing iodine heated by spirit lamp4 ,b4 ,cold flask above to receive the vapour4 ,c ,c4 ,sheet of cardboard to cut off the heat from the spirit lamp4 ,second ,experiment4 ,upon a thin slice of phosphorus place a few small particles of iodine2 the heat produced by the combination of the two elements soon causes the phosphorus to take fire4 ,third ,experiment4 ,heat a brick1 and then throw upon it a few grains of iodine2 by holding a sheet of white paper behind1 the splendid violet colour of the vapour is seen to great advantage4 ,it was by the discovery of iodine in the ashes of sponge--which had long been used as a remedy for goitre1 a remarkable glandular swelling--that this element began to be used for medical purposes1 and the important salt called iodide of potassium is now used in large quantities1 not only in medicine1 but likewise for that most fascinating art1 which has made its way steadily1 and is now practised so extensively1 under the name of photography4 ,page #ach ,,the ,,art ,,of ,,photography4 ,it was the great ,george ,stephenson who asked the late ,dean ,buckland the posing question1 ,can you tell me what is the power that is driving that train8 alluding to a train which happened to be passing at the moment4 ,the learned dean answered1 ,i suppose it is one of your big engines4 ,but what drives the engine8 ,oh1 very likely a canny ,newcastle driver4 ,what do you say to the light of the sun8 ,how can that be8 asked ,buckland4 ,it is nothing else1 said ,stephenson4 ,it is light bottled up in the earth for tens of thousands of years2 light1 absorbed by plants and vegetables1 being necessary for the condensation of carbon during the process of their growth1 if it be not carbon in another form2 and now1 after being buried in the earth for long ages in fields of coal1 that latent light is again brought forth and liberated1 made to work--as in that locomotive--for great human purposes4 ,such was the opinion of the most original and practical man that ever reasoned on philosophy2 and could he have lived to realize the thorough adaptation and business use of light in the art of photography1 he would have said1 man is only imitating nature1 and in producing photographs he must employ the same agent which in ages past assisted to produce the coal4 ,in another part of this elementary work we shall have to consider the nature of light2 here1 however1 the chemical part only of the process of photography will be discussed4 ,many years ago 7in the year #aggg7 ,jenny ,lind's most learned countryman1 ,scheele1 discovered that a substance termed chloride of silver1 obtained by precipitating a solution of chloride of silver with one of salt1 blackened much sooner in the violet rays than in any other part of the spectrum4 ,he says1 ,fix a glass prism at the window1 and let the refracted sunbeams fall on the floor2 in this coloured light put a paper strewed with luna cornua 7horn silver or chloride of silver71 and you will observe that this horn silver grows sooner black in the violet ray than in any of the other rays4 ,in #aggi1 ,priestley directed especial attention to the action of light on plants2 and the famous ,saussure1 following up these and other experiments1 determined that the carbonic acid of plants was more generally decomposed into carbon and oxygen in the blue rays of the spectrum2 these facts probably suggested the bold theory of ,stephenson already alluded to4 ,passing by the intermediate steps of photography1 we come to the second year of the present century1 and find in the ,journal of the ,royal ,institution a paper by ,wedgwood1 entitled ,an ,account of a ,method of ,copying ,paintings upon ,glass1 and of making ,profiles1 by the ,agency of ,light upon ,nitrate of ,silver2 with observations1 by ,h4 ,davy4 ,such a paper would lead the reader to suppose that very little remained to be effected1 and that mere details would quickly establish the art2 but in this case the experimentalists were doomed to ,page #aci disappointment1 as1 after producing their photographs1 they could not make them permanent2 they had not yet discovered the means of fixing the pictures4 ,nearly fourteen years elapsed1 when the subject was again taken up by ,nipc1 of ,chalons1 with little success1 so far as the fixing was concerned2 and twenty-seven years had passed away since the experiments of ,wedgwood and ,davy1 when1 in #ahbi1 ,nipc and ,daguerre executed a deed of co-partnership for mutually investigating the matter4 ,these names would suggest a rapid progress2 but1 strange to relate1 ten years again rolled away1 the father ,nipc had in the meantime died1 and a new contract was made between the son and ,m4 ,daguerre1 when1 in ,january1 #ahci1 the famous discovery was made known to the world1 and in ,july of the same year the ,french ,government granted a pension for life of six thousand francs to ,daguerre1 and four thousand to the son of ,nipc1 who had so worthily continued the experiments commenced by his father4 ,the triumph of the industrious ,french experimentalists was not1 however1 to be unique2 across the ,channel another patient and laborious philosopher had completed on paper precisely the same kind of results as those obtained by ,daguerre on silver plates4 ,mr4 ,fox ,talbot1 in ,england1 had immortalized himself by a discovery which was at once called the ,talbotype1 and for which a patent was secured in #ahda4 ,having thus hastily sketched a brief history of the art1 we may now proceed to the details of the process4 ,first ,experiment4 ,a photogenic drawing1 so called1 but now termed a positive copy1 is prepared by placing some carefully selected paper1 which is free from spots or inequalities 7good paper is now made by several ,english manufacturers1 although some kinds of ,french paper1 such as ,cansan's1 are in high repute71 in a square white hard porcelain dish containing a solution of common salt in distilled water1 #aji grains of salt to the pint4 ,the paper is steeped in this solution for ten minutes1 and then taken out and pressed in a clean wooden press1 or it should be dabbed dry on a clean flat surface with a clean piece of white calico1 which may be kept specially for this duty and not used for anything else1 and it is well that all would-be photographers should understand that neatness and cleanliness are perfectly indispensable in conducting these processes4 ,if a design were required for the armorial bearings of the art of photography1 it might certainly be most fanciful1 but the motto must be cleanliness and neatness1 and in preparing paper it should not be unnecessarily handled1 but lifted by the corners only4 ,the object of dabbing the paper is to prevent the salt accumulating in large quantities in one part of the paper and the reverse in another1 and to distribute the salt equally through the whole4 ,the paper being now dried1 is called salted paper1 and is rendered sensitive when required by laying it down on a solution of ammonio-nitrate of silver1 prepared by adding ammonia to a solution containing sixty grains of nitrate of silver to the ounce of distilled water1 until the whole of the oxide of silver is re-dissolved1 except ,page #adj a very small portion4 ,a few drops of nitric acid are also recommended to be added1 and after allowing the solution to stand1 it may be poured off quite clear1 and is ready for use either in the bath1 or if economy must be rigidly adhered to1 the salted paper may be laid flat on a board1 and held in its place with four pins at the corners1 and then just enough to wet the surface of the paper may be run along the side of a glass spreader1 and the liquid gently drawn over the surface of the salted paper1 which is allowed to dry on a flat surface for a few minutes1 and afterwards hung up by one corner to a piece of tape stretched across the room1 until quite dry1 and then placed in a blotting-book fitting into a case which completely excludes the light4 ,copying-paper should be made at night1 as the day is then free for all photographic operations requiring an abundance of light4 ,it will not keep long1 and should be used the next day4 ,illustration3 ,fig4 #acg4 ,a4 ,the glass spreader with cork handle4 ,b4 ,the silver solution clinging to rod and paper by capillary attraction4 ,c ,c ,c ,c4 ,four pins holding down the paper on a board4--,n4,b4 ,the spreader is made of glass rod three-eighths thick4 ,a piece of lace1 a skeleton leaf1 a sharp engraving on thin paper1 and above all things1 a negative photograph on glass or paper1 is easily copied by placing the prepared paper with the prepared side 7carefully protected from the light7 upwards on any flat surface1 such as plate glass2 upon this is arranged the bit of lace or the negative photograph with the face or picture downwards1 another bit of plate glass is then placed over it1 and weights arranged at the corners2 after exposure to the sun's rays for thirty minutes1 more or less 7according to the dullness or bright aspect of the day71 the picture is brought into a dark room and examined by the light of a candle or by the light from a window covered with yellow calico1 and after placing a paper weight on one corner of the lace1 or ,page #ada negative picture1 or copying paper1 it may be carefully lifted in one part1 and if the copy is sufficiently dark1 is ready for fixing1 but if it is faint the lifted corner is carefully replaced1 the upper glass is laid on1 and the picture again exposed to the light4 ,should the position of the lace or negative be changed during the examination1 re-exposure is useless1 and would only produce a double and confused picture1 as it would be impossible to lay the lace or the negative exactly in the same place again on the copying paper4 ,the manipulations just described are much facilitated by using a copying-frame or press1 which consists of a square wooden frame with a thick plate-glass window2 upon this are placed the negative picture and the copying paper1 and the two are brought in close contact by means of a board at the back pressed by a hand-screw4 7,fig4 #ach47 ,after the photogenic drawing or positive copy is taken1 it is fixed by being placed in a solution of hyposulphite of soda1 consisting of one fluid ounce of saturated solution to eight of water4 ,the saturated solution of hyposulphite of soda is conveniently kept in a large bottle for use1 and in order to improve the colour a very little chloride of gold is added to the fixing solution1 the picture must now be thoroughly washed1 dried1 and pressed4 ,illustration3 ,fig4 #ach4 ,the back of the copying-frame1 showing the hand-screw and pressure-board4 ,the plate glass inside is set in the base of the frame1 and is of course the part exposed to the light4 ,second ,experiment4 ,another mode of preparing the copying paper1 called albumen paper1 is to take the whites of four eggs1 and four ounces of distilled water containing one hundred and sixty grains of chloride of ammonium2 these are beaten up with a fork or a bundle of feathers1 and as the froth is produced it is skimmed off by a silver spoon into another basin1 or a beaker glass1 and being allowed to settle for twelve hours it is strained through fine muslin1 and is ready for use4 ,the best paper is floated on the surface of this liquid for three minutes1 taken out1 and dried at once on a hot plate4 ,in floating paper one corner is first laid down1 and care taken not to enclose any air bubbles1 which would prevent the fluid wetting the paper1 whilst the remainder of the paper is slowly laid upon the surface of the fluid4 ,the albumen paper is excited by laying it for five minutes on a solution of nitrate of silver1 seventy-two grains to the ounce of water1 ,page #adb and when dry it will keep for three days4 ,this copying paper is used in the same manner as the last1 and fresh eggs only must be used in its preparation1 because stale ones soon cause the copy to change and blacken all over from the liberation of sulphur1 which unites with the silver4 ,the colour of the copy is sometimes improved by a solution of hot potash1 and by dipping the well-washed picture1 after the use of the hyposulphite of soda1 in a very dilute solution of hydrosulphuret of ammonia4 ,third ,experiment4 ,in the ,daguerreotype process1 a silver plate1 after being thoroughly cleaned and polished1 is exposed to the vapour of iodine1 and is thus rendered so sensitive that it may be at once exposed in the camera4 ,in the ,talbotype process1 the same principle is apparent1 and paper is prepared by first covering its surface with iodide of silver1 which is afterwards rendered sensitive to the action of light by means of an excess of nitrate of silver1 as follows3-- ,one side of a sheet of selected ,cansan's paper is first covered 7by means of a spreader7 with a solution of nitrate of silver 7thirty grains to the ounce of water71 hung up in a dark room and dried2 it is then immersed in a solution of iodide of potassium of five hundred grains to a pint of distilled water1 for five or ten minutes1 and immediately changes to a yellow colour in consequence of the precipitation of the yellow iodide of silver2 it is then well washed with plenty of water1 and being dried1 may be kept for any length of time1 and is called iodized paper4 ,light has no action whatever upon it4 ,to render the paper sensitive1 three solutions are prepared in separate bottles1 and marked #a1 #b1 #c4 ,no4 #a1 contains a solution of nitrate of silver1 fifty grains to the ounce of water4 ,no4 #b1 glacial acetic acid4 ,no4 #c1 a saturated solution of gallic acid4 ,with respect to ,no4 #c1 ,mr4 ,william ,crookes has shown1 that when a saturated solution of gallic acid is required in large quantities1 that it is better to dissolve at once two ounces of gallic acid in six ounces of alcohol 7#fj over proof72 to hasten solution1 the flask may be conveniently heated by immersion in hot water2 when cold it should be filtered1 mixed with half a drachm of glacial acetic acid1 and preserved in a stoppered bottle for use2 so prepared it will keep unaltered for a considerable length of time4 ,the gallic acid is not precipitated from this solution by the addition of water2 consequently1 if in any case desirable1 the development of a picture may be effected with a much stronger bath than the one usually employed4 ,to obtain a solution of about the same strength as a saturated aqueous solution1 such as ,no4 #c1 half a drachm of the alcoholic solution is mixed with two ounces of water2 but for my particular purpose1 says ,mr4 ,crookes1 referring to the wax-paper process1 ,i prefer a weaker bath1 which is prepared by mixing half a drachm with ten ounces of water4 ,in either case it ,page #adc will be found necessary to add solution of nitrate of silver in small quantities1 as the developing picture seems to require it4 ,returning again to the solutions marked #a1 #b1 #c1 the numbers will assist the memory in mixing the proportions of each4 ,if the paper is required to be used at once1 a drachm of each may be mixed together and spread over the iodized paper 7of course1 in a dark room71 which is then transferred to a clean blotting-book of white bibulous paper1 and being placed in the paper-holder may be taken to the camera and exposed at once4 ,if the paper is not required to be used immediately1 the solutions are mixed in the proportions of the numbers--viz41 one of ,no4 #a1 two of ,no4 #b1 three of ,no4 #c2 and in making the mixture1 it is advisable to keep a measure specially for ,no4 #c1 the gallic acid1 or else the measure1 if used for the three solutions1 will have to be washed out every time1 which is very troublesome1 particularly where water is not plentiful4 ,if the excited paper is required to be kept some hours before use1 ,no4 #c must be added in still larger proportion1 as much as ten or even twenty measures of ,no4 #c to two of ,no4 #b1 and one of ,no4 #a1 being used1 and even this large dilution is frequently insufficient to prevent the paper spoiling in hot weather2 therefore if the temperature is high1 too much reliance must not be placed on this paper1 as it is peculiarly disappointing1 after walking some miles to romantic and beautiful scenery1 to find1 when developing the pictures in the evening1 that the paper used was all spoilt before exposure2 and it will be seen presently that when the excited paper is to be carried about for use1 it is better to adopt the wax-paper process4 ,after the excited iodized paper is exposed in the camera--and the time of exposure cannot be taught1 as that speciality is only acquired by experience1 and may vary from five to thirty minutes1 or even more--the invisible picture is developed and rendered visible1 not by exposure to the vapour of mercury1 as in ,daguerre's process with silver plates1 but by a mixture of one of ,no4 #a with four of ,no4 #c4 ,the development is carefully watched by looking through the negative placed before a lighted candle1 and the time of development may vary from ten to thirty minutes1 and all the time the picture must be kept wet with the solution1 so that it is better perhaps to make a bath of the solution and lay the picture on its surface than to pour the liquid over the picture4 ,after the development is matured1 the picture is now washed in clean water1 and fixed temporarily1 if required1 by immersion in a bath containing #bjj grains of bromide of potassium in one pint of water1 or permanently by the hyposulphite of soda1 made by mixing one part of a saturated solution with five or ten of water1 or one ounce of the salt to six or twelve of water2 but1 as before mentioned1 it is better to keep a ,winchester quart full of a saturated solution of hyposulphite of soda1 and then it is always ready for use instead of employing the weights and scales1 and continually weighing out portions of the salt4 ,the picture after fixing is thoroughly washed with water1 and being ,page #add dried is now placed between the folds of a wax book--i4e41 some leaves of blotting-paper are kept saturated with white wax1 and when a picture is placed between them1 and a hot iron passed over the outside sheet1 the wax enters the pores of the paper1 and after removing any excess of wax by passing the picture through a book of bibulous paper1 over which the hot flat iron is passed1 the negative picture at last is ready for use1 and any number of positive copies may be taken from it1 as already described in the first experiment1 page #aci4 ,this mode of manipulation is called the ,talbotype1 and before dismissing the subject another process of iodizing the paper may be explained4 ,to a solution of nitrate of silver of twenty1 thirty1 or fifty grains to the ounce of water1 a sufficient number of the crystals of iodide of potassium is added1 first to produce the yellow iodide of silver1 and then to dissolve it1 so that the yellow precipitate appears with a small quantity1 and disappears with an excess of the iodide4 ,if this solution is spread over sheets of paper1 and these latter then placed in a bath of water1 the iodide of silver is precipitated on the surface1 and after plenty of washing to remove the excess of iodide of potassium1 the paper may be dried1 and will keep for any length of time without change4 ,this paper may be excited1 exposed1 developed1 fixed1 and waxed1 as already explained4 ,fourth ,experiment4 ,the ,wax-paper ,process4 ,this mode of taking negative photographs begins where the talbotype ends--viz41 by first waxing the paper perfectly and evenly1 as already explained1 ,cansan's negative paper being preferred4 ,the wax paper is now well soaked in a bath1 made by dissolving one hundred grains of iodide of potassium1 six grains of cyanide of potassium1 four grains of fluoride of potassium1 ten grains of bromide of potassium1 ten grains of chloride of sodium1 in one pint of fresh whey1 with the addition of a little alcohol and a few grains of iodine4 ,when soaked in this solution for about one hour1 the paper is taken out and hung up to dry4 ,n4,b4 ,with respect to iodizing the wax paper1 it is almost better to obtain it ready prepared1 and then every sheet may be relied on4 ,mr4 ,melhuish1 of ,blackheath and ,holborn1 supplies it in any quantity1 and his paper never fails2 the operator has then only to perform the sensitizing and developing processes4 ,to render the iodized paper sensitive it is immersed for about six minutes in a bath containing a solution of nitrate of silver 7thirty-five grains to the ounce of water1 with forty drops of glacial acetic acid72 the paper is now removed1 and washed in two trays of common clear rain-water or distilled water1 and is then dried off between folds of blotting-paper4 ,this process may be performed on the previous evening by the light of a candle1 or by day in a room lit by one window covered with four thicknesses of yellow calico1 and after the paper is dry it will keep for three ,page #ade weeks or a month1 and may be exposed in a camera with a three-inch lens of eighteen-inch focus1 with the inch diaphragm1 on a bright day from five to fifteen minutes2 in bad weather the exposure must be longer4 ,the picture may be carried home and rendered visible or developed by immersion in a bath containing a saturated solution of gallic acid1 and as the developing continues1 a few drops of the sensitizing solution of nitrate of silver and glacial acetic acid may be added4 ,finally1 the picture is fixed by immersion for a quarter of an hour in a solution of hyposulphite of soda 7four ounces of the crystal to one pint of water1 or one part of the saturated solution to eight of water71 and being well washed1 is then dried1 hung before the fire to melt the wax1 and is now ready to print from4 ,fifth ,experiment4 ,albumen on ,glass ,process4 ,albumen is the scientific name for the white of egg1 of which four ounces by measure are mixed with one ounce and a half of distilled water1 and after being whisked to a froth1 are removed by a spoon into another basin or a beaker glass1 and allowed to stand for several hours and then filtered4 ,mr4 ,crookes has recommended a very ingenious1 simple1 and useful filter4 7,fig4 #aci47 ,he says3 ,this simple and inexpensive piece of apparatus1 which any instrument maker or glass-blower can supply at a few hours' notice1 will be found invaluable in almost every photographic process on glass4 ,the sponge has this great advantage over all other kinds of filters1 that thick gelatinous liquids--e4g41 honey1 albumen1 gelatine1 meta-gelatine1 or the various preservative syrups--flow through it with the utmost readiness2 whilst at the same time dust1 air bubbles1 or froth1 and dried particles floating in the liquid1 are effectually kept back1 and if fitted with stoppers1 collodion might be filtered in it2 or if the ends were fitted together with a bit of flexible pipe1 the stoppers might be dispensed with altogether4 ,illustration3 ,fig4 #aci4 ,a ,b4 ,glass tube1 bent as in picture4 ,c4 ,piece of damp sponge squeezed into the head of the tube4 ,any liquid poured in at ,b will flow through the sponge until it has attained the same level in ,a4 ,having poured the albumen on a perfectly clean glass plate1 taking care to have sufficient to run freely over the surface of the glass1 the excess is then gently drained off and the plate turned so as to have the coated side downwards2 it is then fixed in a sling made by taking a stout bit of string about three feet long1 which is doubled and knotted at the fold1 leaving the two ends free2 two small triangles or stirrups of silver wire looped at one corner are now tied on to the ends of the string1 and these form a support for the opposite edges of the glass plate to rest on2 the two strings are knotted together at a ,page #adf convenient distance from the stirrups to prevent the glass slipping out1 and the plate is now rotated rapidly over a heated metallic surface1 such as an iron box containing some burning charcoal or the warming pan1 care being taken to avoid dust as much as possible1 and to use only the whites of new-laid eggs4 7,fig4 #adj47 ,the glass plate1 covered with dry albumen1 is now iodized to a straw colour by exposure over a box containing iodine1 as in the ,daguerreotype process1 and is sensitized by immersion for three or four minutes in a bath containing a solution of nitrate of silver 7twenty-five grains to an ounce of water72 the plate is afterwards washed in distilled water and left to dry spontaneously1 of course in a darkened room4 ,the plates may then be placed ready for use in a very ingenious tin box devised by ,mr4 ,crookes1 which keeps them perfectly light-tight even in the sun1 and at the same time is less bulky than the ordinary wooden ones4 ,it is made of tin plate1 the cover sliding tight over the top1 and more than half way down the sides2 light is further excluded by means of an outer jacket of tin1 which is soldered to the box a little below the centre4 ,the cover thus slides between the case and the jacket1 and renders injury to the plates by the entrance of light an impossibility4 7,fig4 #ada47 ,illustration3 ,fig4 #adj4 ,a4 ,loop for finger4 ,b4 ,the knot which prevents the stirrups of silver wire1 ,c ,c1 slipping off the corners of the glass plate4 ,d ,d4 ,the opposite corners of the glass plate on which the stirrups are placed4 ,illustration3 ,fig4 #ada4 ,a ,a4 ,tin box1 with partitions to hold glass plates1 ,b ,b4 ,the outer jacket1 between which and the box1 ,a1 the lid or cover1 ,c1 slides4 ,the sensitive albumenized glass plate is exposed in the camera from fifteen to thirty minutes1 and developed 7much in the same way as the paper pictures7 with one ounce of a saturated ,page #adg solution of gallic acid containing ten or fifteen drops of the sensitizing solution4 ,the plate is usually placed on a levelling stand1 and the solution poured on the glass plate2 the development is slow1 and may be quickened sometimes by the application of heat4 ,the picture is fixed by immersion for a short time in a bath containing one part of a saturated solution of hyposulphite of soda in eight of water4 ,the pictures produced by this process are exquisitely defined1 provided always the camera is well focussed1 and to assist this operation a magnifying glass may be employed4 ,after removal from the hyposulphite of soda the plate is well washed with water1 and being allowed to dry spontaneously1 is now ready to print from4 ,sixth ,experiment4 ,the ,collodion on ,glass ,process4 ,the glass plates for this1 as well as the albumen on glass process1 should be cleaned by rubbing them over first with a mixture of ,tripoli powder and ammonia1 which is washed off under a tap1 and the glass being drained is rubbed dry and polished with a clean calico duster kept exclusively for this purpose4 ,the iodized collodion is now poured on1 and the excess returned to the bottle4 ,collodion can be made very easily1 but if prepared without due precautions1 it cannot be used afterwards1 and reminds one of the old story of the enthusiastic son1 who1 when asking his father's permission to espouse the beloved1 enumerated amongst her other accomplishments1 the fact that she could make a pudding1 and was answered by the bluff question1 ,but can you eat it afterwards8 ,so it is with collodion3 a great deal of messing and loss of time is saved by purchasing it of the various makers1 amongst whom may be specially noticed ,mr4 ,richard ,thomas1 of #aj1 ,pall ,mall1 who has devoted the whole of his attention to the preparation of this important photographic chemical1 and with a success which his numerous patrons can well testify4 ,the collodion is sold either mixed with the iodizing solution1 or the two can be obtained separately1 with directions on the bottles as to the quantities to be mixed together4 ,the plate covered with the iodized collodion is quickly transferred to a bath containing a solution prepared in the following manner3--,dissolve four ounces of nitrate of silver in eight ounces of water1 and to this add twenty grains of iodide of potassium in one ounce of water2 shake them together1 and then pour the whole into fifty-six ounces of distilled water1 and in half an hour add one ounce of alcohol and half an ounce of ether2 agitate the whole and filter the next morning4 ,the collodion plate is kept in this solution for a certain period1 only learnt by experience1 and should be occasionally lifted out to see if a uniform transparency is obtained2 say that the immersion may be continued for five minutes1 it is now ready for the camera1 and may be exposed from about one to two minutes1 or more if the light is deficient2 the time of exposure is also a matter of practice1 mere directions can be of no use in this stage of the process4 ,the picture is developed on a levelled stand1 with a solution of three ,page #adh grains of pyrogallic acid in three ounces of water1 to which sixty drops of glacial acetic acid have been added4 ,when fully developed the plate is washed with water and fixed with a solution of hyposulphite of soda1 consisting of one part of the saturated solution to eight of water1 again thoroughly but gently washed1 so as not to endanger the separation of the film from the glass2 it is allowed to dry spontaneously1 and being coated with amber varnish 7a solution of amber in chloroform7 is now ready to print from4 7,fig4 #abc47 ,it is1 perhaps1 hardly necessary to add1 that the sensitizing and developing processes must be performed in a dark room4 ,illustration3 ,fig4 #adb4 ,a4 ,glass or gutta-percha bath to hold the sensitizing solution4 ,b4 ,glass1 with piece cemented on the end to hold the prepared glass plate1 ,c1 whilst dipped in the bath1 ,a4 ,the plate ,c has a cross in one corner to show prepared side4 ,illustration3 ,fig4 #adc4 ,first effect of peripatetic photography on the rural population4 ,page #adi ,,bromine4 ,bromine 7,greek3 brmos1 a bad odour74 ,symbol1 ,br4 ,combining proportion1 #hj4 ,specific gravity1 #b4iff4 ,in a previous portion of this work1 the connexion between chlorine1 iodine1 and bromine has been pointed out2 and as we have to notice the colour of the element bromine1 the chromatic union of the triad may be alluded to4 ,these elements present very nearly all the colours of the spectrum3 ,bromine red to orange4 ,chlorine yellow to green4 ,iodine blue1 indigo1 violet4 ,these three elements also furnish examples of the three conditions of matter2 iodine being a solid1 bromine a fluid1 chlorine a gas2 the relation of their combining proportions is also curious3 as might be expected1 the fluid bromine takes an intermediate position1 and 7according to the axiom that half the sum of the extremes is equal to the mean7 by dividing the combining proportions of iodine and chlorine1 and adding them together1 we have1 as nearly as possible1 the combining proportion of bromine3 ,chlorine #ce #b #ag4ge ,iodine #abf #b #fc ----- #hj4ge ,the combining proportion of bromine is #hj1 but #hj4ge is so near1 that it may reasonably be conjectured future experiments will reduce the number of the three elements1 and may prove that they are only modifications of a single one4 ,this is the only kind of alchemy which is tolerated in the nineteenth century1 and any philosopher who will reduce the number of elements1 and prove that some of them are only modifications of others1 will achieve a renown that must transcend the clat of all previous discoverers4 ,bromine was discovered by ,balard1 in #ahbf1 and1 like chlorine and iodine1 is a constituent of sea water4 ,the chief source of bromine is a mineral spring at ,kreutznach1 in ,germany4 ,the process by which it is obtained offers a good example of chemical affinity2 the water of the mineral spring is evaporated1 all crystallizable salts removed1 and a current of chlorine gas passed through the remaining solution1 which changes to a yellow colour1 in consequence of the liberation of the bromine by the combinations of chlorine with the bases previously united with the former2 the liquid is then shaken with ether1 which dissolves out the bromine4 ,in the next place1 the etherial solution is agitated with strong solution of potassa1 and is thus obliged to part with the bromine which is converted into bromate of potassa2 this is ultimately changed by fusion to bromide of potassium2 and by distillation with black oxide of manganese and sulphuric acid1 the bromine is finally obtained4 ,six ,page #aej processes are therefore necessary before the small quantity of bromine contained in the mineral spring-water1 is separated4 ,first ,experiment4 ,bromine is a very heavy fluid1 which should be preserved by keeping it in a bottle covered with water2 when required1 a few drops may be removed by means of a small tube1 and dropped into a warm bottle1 which is quickly filled with the orange-red vapour4 ,if some phosphorus is placed in a deflagrating spoon1 and exposed to the action of bromine vapour1 it takes fire spontaneously4 ,second ,experiment4 ,powdered antimony sprinkled into the vapour of bromine immediately takes fire4 ,third ,experiment4 ,a burning taper immersed in a bottle containing the vapour of bromine is gradually extinguished4 ,fourth ,experiment4 ,liquid bromine exposed to a freezing mixture of ice and salt1 or reduced to a temperature of about eight degrees below zero1 solidifies into a yellowish-brown1 brittle1 crystalline mass4 ,fifth ,experiment4 ,a solution of indigo shaken with a small quantity of the vapour of bromine is quickly bleached4 ,many substances1 when brought in contact with liquid bromine1 combine with explosive violence1 and therefore experiments with liquid bromine are not recommended1 as all the most instructive and conclusive results can be obtained by the use of the vapour of bromine1 which is easily procured by allowing a few drops to fall into a warm1 dry bottle4 ,bromine1 as already mentioned1 is used in the art of photography4 ,,fluorine4 ,symbol1 ,f4 ,combining proportion1 #ai4 ,this singular element seems almost to embody the ancient idea of the alchemists1 being a sort of alkahest1 or universal solvent2 or in plainer language1 its affinities for other bodies are so powerful1 that it attacks every substance 7not even excepting gold71 at the moment of its liberation1 and combines therewith1 so that its isolation has not yet been effected4 ,chemists who assert that they have been able to obtain fluorine in the elementary condition1 pronounce it to be a gas which possesses the colour of chlorine2 but the experiments1 as hitherto conducted1 render that statement extremely doubtful4 ,page #aea ,the only interesting fact connected with fluorine1 is the remarkable property of attacking glass and other silicious bodies1 belonging to its combination with hydrogen gas1 called hydrofluoric acid4 ,this acid is easily obtained and used by placing some powdered fluorspar in a leaden tray six inches square and two inches deep4 ,if sulphuric acid is now mixed with the powdered spar1 so as to form a thin paste1 and heat applied1 the vapour of the hydrofluoric acid quickly rises1 and can be employed to etch a glass plate upon which a drawing may have been previously traced by scratching away the wax1 with which it is first coated4 ,by heating the glass plate before a fire1 a sufficient quantity of wax is soon melted on to it by merely rubbing the wax against the glass plate2 any excess should be avoided1 if a well-executed drawing is required to be etched on its surface4 7,fig4 #add47 ,illustration3 ,fig4 #add4 ,a ,a ,a4 ,the glass plate1 with the waxed side downwards1 placed on the leaden tray containing the fluorspar and sulphuric acid4 ,b4 ,spirit lamp4 ,the wax plate must not remain too long over the leaden tray1 as the heat is apt to melt the wax1 when the acid not only attacks those parts from which the wax has been removed by the etching needle1 but also the surface of the glass generally1 and thus the clearness of the design is spoilt4 ,after exposure--and it is as well to prepare two or three glass plates for the experiment--the wax is quickly removed by rubbing and washing with oil of turpentine1 and the design 7beautifully etched into the glass7 is then apparent4 ,,chapter ,,xii4 ,,carbon1 ,,boron1 ,,silicon1 ,,selenium1 ,,sulphur1 ,,phosphorus4 ,this group of non-metallic elements has been frequently styled ,metalloids1 meaning substances allied to1 but not possessing1 all the properties belonging to a metallic substance2 and therefore perhaps the expression1 non-metallic solids1 is the best that can be adopted4 ,they may be subdivided into two classes of three each1 which have properties more or less allied to each other--viz41 ,carbon1 ,boron1 ,silicon2 and ,selenium1 ,sulphur1 ,phosphorus4 ,page #aeb ,,carbon4 ,symbol1 ,c2 ,combining ,proportion1 #f4 ,this element has almost the property of ubiquity1 and is to be found not only in all animal and vegetable substances1 in common air1 sea1 and fresh water1 but also in various stones and minerals1 and especially in chalk and limestone4 ,there is1 perhaps1 no element which offers a greater variety of amusing experiments and elementary facts than carbon1 whether it be considered either in its simple or combined state4 ,a piece of carbon1 in the shape of the ,koh-i-,noor1 was one of the chief attractions at the first ,exhibition in ,hyde ,park4 ,the diamond is the hardest and most beautiful form of charcoal2 how it was made in the great laboratory of nature1 or how its particles came together1 seems to be a mystery which up to the present time has not yet been solved1 at all events no artificial process has yet produced the diamond4 ,sir ,d4 ,brewster1 speaking of the ,koh-i-,noor1 remarks that on placing it under a microscope1 he observed several minute cavities surrounded with sectors of polarized light1 which could only have been produced by the expansive action of a compressed gas or fluid1 that had existed in the cavities when the diamond was in the soft state4 ,now it is known that bamboo1 which is of a highly silicious nature1 has the property of depositing in its joints a peculiar form of silica1 called tabasheer4 ,silicon is one of the triad with carbon--i4e41 it is allied to carbon on account of certain analogies2 may it not then be supposed that1 in times gone by1 ages past1 when the atmosphere was known to be highly charged with carbonic acid gas1 there might possibly have existed some peculiar tree which had not only the power of decomposing carbonic acid 7possessed by all plants at the present period71 but was enabled1 like the bamboo1 to deposit1 not silica1 which is the oxide of silicium1 but carbon1 the purest form of charcoal--viz41 the diamond8 ,speculation in these matters is ever more rife than stern proof1 and it may be stated1 that all attempts to manufacture this precious gem 7like those of the alchemists with gold and silver7 have most signally failed4 ,first ,experiment4 ,box and various woods1 dried bones1 and different organic matters1 placed in a nearly close iron or other vessel1 and heated red hot1 so that all volatile matter may escape1 leave behind a solid black substance called charcoal4 ,if that kind obtained from bones1 and termed bone black or ivory black1 is roughly powdered1 and placed in a flask with some solution of indigo or some vinegar1 or syrup obtained by dissolving common moist sugar in water1 and boiled for a short period1 the colour is removed1 and on filtering the liquid it is found to be as clear and colourless as water1 provided sufficient ivory black has been employed4 ,page #aec ,second ,experiment4 ,charcoal is a disinfectant1 and is used for respirators2 it has even been recommended medically1 and charcoal lozenges can be bought at various chemists' shops4 ,if a few drops of a strong solution of hydrosulphuret of ammonia 7which has the agreeable odour belonging to putrid eggs7 is mixed with half a pint of water1 it will of course smell strongly1 and likewise precipitate ,goulard water1 or a solution of acetate of lead black2 but on shaking the water with a few ounces of charcoal1 it no longer smells of sulphuretted hydrogen1 and if filtered and poured into a solution of lead does not turn it black4 ,this chemical action of charcoal1 independent of its seeming mechanical attraction for colouring matter1 would appear to show that the pores of charcoal contain oxygen1 which in that peculiar condensed state destroys colouring matter1 and oxidizes other bodies4 ,third ,experiment4 ,a very satisfactory experiment1 proving that the diamond and plumbago or black lead are identical with charcoal1 although differing in outward form and purity1 can be made at a little cost1 by purchasing a fragment of refuse diamond1 called boart1 of ,mr4 ,tennant of the ,strand4 ,a small piece costs about five shillings4 ,the fragment should be carefully supported by winding some thin platinum wire round it1 as1 if the wire is too thick1 it cools down the heat of the bit of diamond and prevents it kindling in the oxygen gas4 ,a difficulty may arise in preparing the fragment1 in consequence of the wire continually slipping off4 ,the boart should therefore be grasped by the thumb and first finger1 and the wire wound round2 then it must be carefully turned and again wound across with the platinum wire1 as in the sketch below4 7,fig4 #ade47 ,illustration3 ,fig4 #ade4 ,a4 ,the platinum wire4 ,b4 ,the fragment of boart or refuse diamond4 ,a piece of black lead 7so called7 may now be taken from a lead pencil and also supported by platinum wire2 likewise a bit of common bark charcoal or hard coke4 ,three bottles of oxygen should now be prepared from chlorate of potash and oxide of manganese1 an extra bottle being provided for the diamond in case there should be any failure in its ignition4 ,the bark charcoal can be first ignited by holding a corner in the spirit lamp for a few seconds2 when plunged into oxygen it immediately kindles and burns with rapidity1 and if the cork is well fitted1 the product of combustion--viz41 carbonic acid gas--is retained for future examination4 ,the small piece of black lead is next heated red hot in the flame of the spirit lamp1 and being attached by its platinum support to a stiff copper wire thrust through a cork1 which fits the bottle of oxygen1 is placed whilst red hot in the gas1 and continues to glow until consumed4 ,the fragment of diamond is by no means1 however1 so ,page #aed easily ignited1 the flame of the spirit lamp must be urged upon it with the blowpipe2 when quite red hot1 an assistant may remove the stopper from the bottle of oxygen1 and the person heating the diamond should plunge it instantly into the gas2 if this is dexterously managed1 the fragment of boart glows like a little star1 and the combustion frequently continues till the piece diminishes so much that it falls out of its platinum support4 ,sometimes the diamond cools down without igniting1 the same process must therefore be repeated1 and a few extra bottles of oxygen will prevent disappointment1 as every failure destroys the purity of the gas by admixture with atmospheric air when the stopper is removed4 7,fig4 #adf47 ,illustration3 ,fig4 #adf4 ,a4 ,bottle containing bark charcoal4 ,b4 ,ditto the plumbago or black lead4 ,c4 ,ditto the diamond4 ,the combustion having ceased in the three bottles1 the corks are removed1 and the glass stoppers again fitted for the purpose of testing the products1 which offer no apparent indication of any change1 as oxygen and carbonic acid gas are both invisible4 ,in each bottle a new combination has been produced2 the charcoal1 the black lead1 the diamond have united with the oxygen1 in the proportion of six parts of carbon to sixteen parts of oxygen1 to form twenty-two parts of carbonic acid gas1 which may be easily detected by pouring into each bottle a small quantity of a solution of slacked lime in water1 called lime water4 ,this test is easily made by shaking up common slacked lime with rain or distilled water for about an hour1 and then passing it through a calico or paper filter4 ,the test1 though perfectly clear when poured in1 becomes immediately clouded with a white precipitate1 usually termed a milkiness1 no doubt in allusion to the ,london milk1 which is supposed to contain a notable proportion of chalk and water1 for in this case the precipitate is chalk1 the carbonic acid from the diamond and the charcoal having united with the lime held in solution by the water and formed carbonate of lime1 or chalk1 a substance similar in composition to marble1 limestone1 ,iceland or double refracting spar1 these three being nearly similar in composition1 and differing only1 like carbon and the diamond1 in external appearance4 ,page #aee ,the milkiness1 however1 must not be held as conclusive of the presence of carbonic acid gas until a little vinegar or other acid1 such as hydrochloric or nitric1 has been finally added2 if it now disappears with effervescence 7like the admixture of tartaric acid1 water1 and carbonate of soda71 the little bubbles of carbonic acid gas again escaping slowly upwards1 leaving the liquid in the three bottles quite clear1 then the experimentalist may sum up his labours with these effects1 which prove in the most decisive manner that common charcoal1 black lead1 and the diamond1 are formed of one and the same element--viz41 carbon4 ,fourth ,experiment4 ,having effected the synthesis 7or combining together7 of the diamond and oxygen1 it is no longer possible to recover it in its brilliant and beautiful form4 ,if the product of combustion is retained in a flask made of thin1 hard glass1 and two or three pellets of the metal potassium are placed in directly after the diamond has ceased to burn1 and the flame of a spirit lamp applied till the potassium ignites1 then the metal1 by its great affinity for oxygen1 takes away and separates it again from that which was formerly the diamond2 but instead of the jewel being deposited1 there is nothing but black1 shapeless1 and minute particles of carbon obtained1 if the potash produced is dissolved in water1 and the charcoal separated by a filter4 ,fifth ,experiment4 ,chalk is made by uniting carbonic acid gas with lime2 it may therefore be employed as a source of the gas1 by placing a few lumps of chalk1 or marble1 or limestone1 in a bottle such as was used in the generation of hydrogen gas2 on the addition of some water and hydrochloric acid1 effervescence takes place from the escape of carbonic acid gas1 and the cork and pewter pipe being adapted1 it may be conveyed by its own gravity into glasses1 jugs1 or any other vessels1 and a pneumatic trough will not be required4 ,carbonic acid gas has a specific gravity of #a4ebi1 and is therefore rather more than half as heavy again as atmospheric air4 ,sixth ,experiment4 ,in order to satisfy the mind of the operator that the gas obtained from chalk is similar to the product of combustion from the diamond1 some lime-water may be placed in a glass1 and the gas from the bottle allowed to bubble through it2 instantly the same milkiness is apparent1 which again vanishes on the addition of acid4 ,and this experiment is rendered still more striking if a lighted taper be placed in the glass just after the addition of the acid1 when it will be immediately extinguished4 ,seventh ,experiment4 ,if a lady's muff-box1 supported by threads or chains1 is hung on one end of a scale-beam1 and counterbalanced by a scale pan and a few shot1 it is ,page #aef immediately depressed on pouring into the muff-box a quantity of carbonic acid gas1 which may have been previously collected in a large tin vessel4 ,after showing the weight of the gas1 the box is detached from the scale-beam1 and the contents poured upon a series of lighted candles1 which are all extinguished in succession4 7,fig4 #adg47 ,illustration3 ,fig4 #adg4 ,a4 ,carbonic acid gas poured out of the tin box into ,b1 the muff-box4 ,b ,b4 ,detached muff-box1 and candles extinguished by the carbonic acid gas poured from it4 ,eighth ,experiment4 ,the property of carbonic acid gas of extinguishing flame1 as compared with the contrary property of oxygen1 is nicely shown by first passing into a large and tall gas jar one half of its volume of oxygen gas2 a large cork perforated with holes may be introduced1 so as to float upon the surface of the water in the gas jar1 and is usefully employed to break the violence with which the carbonic acid enters the gas jar1 as it is passed in to fill up the remaining half volume of the gas jar1 which now contains oxygen at the top1 and carbonic acid gas at the bottom4 ,on testing the contents of the jar with a lighted taper1 it burns fiercely in the oxygen1 but is immediately extinguished in the ,page #aeg carbonic acid gas1 being alternately lighted and put out as it is raised or depressed in the gas jar4 ,ninth ,experiment4 ,a little treacle1 water1 and a minute portion of size1 may be placed with some yeast in a quart bottle1 to which a cork and pewter or glass pipe is attached2 directly the fermentation begins1 quantities of carbonic acid gas may be collected1 and tested either with lime-water or the lighted taper4 ,tenth ,experiment4 ,some clear lime-water placed in a convenient glass is quickly rendered milky on passing through it the air from the lungs by means of a glass tube2 thus proving that respiration and 7as shown by the ninth experiment7 fermentation1 as well as the combustion of charcoal1 produce carbonic acid gas4 ,eleventh ,experiment4 ,illustration3 ,fig4 #adh4 ,a ,a4 ,the box model of the ,grotto del ,cane4 ,b ,b4 ,cardboard fixed in front of box1 and painted to imitate rocks4 ,c4 ,carbonic acid gas bottle1 with bent tube passing through hole in the side of the box4 ,a taper introduced at ,d burns in the upper1 and is extinguished in the lower1 part of the model4 ,carbonic acid gas is not only generated by the above processes1 but is liberated naturally in enormous quantities from volcanoes1 and from certain soils3 hence the peculiar nature of the air in the ,grotto del ,cane4 ,dogs thrust into this cave drop down immediately1 and are immediately revived by the tender mercies of the guides1 who throw them into the adjoining lake4 ,this natural phenomenon is well imitated by taking a box1 open at the top1 and nailing on to it a frame of cardboard1 ,page #aeh which may be painted to represent rocks1 taking care that a portion 7about three inches deep7 at the lower part is well pasted to the box at the edges1 so that the gas may be retained2 a hole is perforated at the top side to admit a lighted taper1 and another at the side for the pipe from the carbonic acid bottle2 when the bottom is filled with gas1 a taper is applied1 which is found to burn in the upper part1 but is immediately extinguished when it reaches the lower division1 where the three inches of pasteboard prevent it falling out3 thus showing in a simple manner why a guide may enter the cave with impunity1 whilst the dog is rendered insensible because immersed in the gas4 7,fig4 #adh47 ,twelfth ,experiment4 ,many fatal accidents have occurred in consequence of the air in deep pits1 graves1 c41 becoming unfit for respiration by the accumulation of carbonic acid gas1 which may arise either from cavities in the soil1 where animal matter has undergone decomposition1 or it may happen from the depth and narrowness of the hole or well preventing a proper draught or current of air1 so that it becomes foul by the breathing of the man who is digging the pit4 ,air which contains one or two per cent4 of carbonic acid will support the respiration of man1 or maintain the flame of a candle2 but it produces the most serious results if inhaled for any length of time2 a lighted candle let down into a well 7suspected to contain foul air7 before the descent of the person who is to work in it1 may burn1 but does not indicate the presence of the small percentage of the poison1 carbonic acid4 ,frequently no trouble is taken to test the air with a lighted candle2 a man is lowered by his companions1 who see him suddenly become insensible1 another is then lowered quickly to rescue him1 and he shares the same fate2 and indeed cases have occurred where even a third and a fourth have blindly and ignorantly rushed to their death in the humane attempt to rescue their fellow creatures4 ,what is to be done in these cases8 ,are the living to remain idle whilst the unfortunate man is suffocating rapidly at the bottom of the pit8 ,no2 provided they do not venture themselves into the pit1 they may try every known expedient to alter the condition of the foul air1 so as to enable them to descend to the rescue4 ,one should be despatched to any neighbouring house or cottage for a pan of burning coals2 if any slacked lime is to be had1 it may be rapidly mixed with water1 and poured down the side of the pit2 a bundle of shavings set on fire and let down1 keeping it to one side1 so as to establish a current2 or even the empty buckets constantly let down empty and pulled up full of the noxious air1 may appear a somewhat absurd step to take1 but under the circumstances any plan that will change the air sufficiently to enable another person to descend must be adopted2 in proof of which the following experiments may be adduced3 ,fill a deep glass jar with carbonic acid1 and ascertain its presence with a lighted taper2 if a beaker glass to which a string is attached is let down into the vessel and drawn up1 and then inverted over a lighted ,page #aei taper1 the utility of this simple plan is at once rendered apparent2 the beaker glass represents the empty bucket1 and can be let down and pulled up full of carbonic acid until a sensible change in the condition of the atmosphere is produced4 ,the best plan1 however1 is to set the air in motion by heat obtained from burning matter1 or even a kettle of boiling water1 lowered by a cord1 and this fact is well shown by putting a small flask full of boiling water1 and corked1 at the bottom of the deep glass jar containing the carbonic acid gas1 which rises like other gases when sufficiently heated1 and passing away1 mixes with the surrounding air4 7,fig4 #adi47 ,illustration3 ,fig4 #adi4 ,a4 ,deep jar containing carbonic acid gas1 which is being removed by the little glass bucket4 ,b4 ,jar containing corked flask of boiling water on a pad2 the heated gas rises and the cold air descends to take its place4 ,thirteenth ,experiment4 ,carbonic acid gas dissolved in water under considerable pressure1 forms that most agreeable drink called soda-water2 the gas is not only useful in this respect1 but has been applied most successfully by ,mr4 ,gurney to extinguish a fire on a gigantic scale1 which had been burning for years in the waste of a coal mine in ,scotland4 ,the same gas1 generated suddenly by the combustion of a mixture of nitre1 coke dust1 and clay1 or plaster of ,paris1 in vessels of a peculiar construction1 has formed the subject of a patent by ,phillips1 since merged into the ,fire ,annihilator ,company4 ,the instrument is peculiarly adapted for shipping1 and might1 if properly used1 be the means of saving many ships and valuable lives4 7,fig4 #aej47 ,its practical value is established by the test of actual use3 in the streets1 by the ,leeds ,fire ,brigade1 and by firemen of the ,fire ,annihilator ,company1 temporarily stationed at ,liverpool and ,manchester4 ,the ,fire ,annihilator has been formally recognised by the ,government ,emigration ,commissioners1 who introduced into the ,passengers' ,act1 #aheb1 in #bd1 the alternative1 ,or other apparatus for extinguishing fire1 with distinct reference to this invention1 and subsequently by formal order authorized their officers to pass ships carrying ,fire ,annihilators4 ,page #afj ,illustration3 ,fig4 #aej4 ,a4 ,a carriage with six fire annihilators1 ,no4 #e size1 fitted with moveable pipes4 ,the body of the carriage forms a tank for forty gallons of water2 the tank is filled at a bunghole in the platform2 a patent tap is fitted to the rear of the carriage2 a spigot is placed near the end upright of the rail2 a hand-pump is placed in the box at rear of carriage2 a leather bucket with foot-holds and three canvas buckets are hung on the carriage2 a hammer for removing and driving on the cover of the fire annihilator1 and a nut wrench for the ,no4 #aj truck1 are placed in the box4 ,b4 ,a fire annihilator1 ,no4 #aj size1 with moveable pipe1 on a spring truck1 is attached to the carriage4 ,the battery is fitted with shafts for one horse4 ,a pole is also provided to fix across the shafts1 so that the battery may be drawn by hand4 ,illustration3 ,fig4 #aea4 ,a4 ,tank containing acid1 communicating by a pipe with ,b1 half filled with chalk and water4 ,c ,c ,c ,c4 ,pipes conveying carbonic acid from the generator ,b1 to the ceiling1 where it is discharged from numerous holes on the fire beneath4 ,monsieur ,adolphe ,girard has proposed that all houses should be provided with an apparatus for the generation of carbonic acid gas1 placed ,page #afa outside the building1 which is to be conveyed along the ceiling by means of pipes perforated with numerous holes1 and to be put in operation directly a fire breaks out4 ,this plan1 however ingenious1 could hardly supply the carbonic acid gas with sufficient rapidity1 and it is to be feared would utterly fail in practice4 7,fig4 #aea47 ,,boron4 ,symbol1 ,b2 combining proportion1 #aj4i4 ,discovered by ,homberg1 in #agjb1 in borax1 which is a biborate of soda 7,na,o1#b;,,bo#c71 and is used very extensively in the manufacture of glass2 also for glazing stoneware and soldering metals2 it is also a valuable flux in various crucible operations1 whilst in testing minerals with the blowpipe it is invaluable4 ,borax is made either from tincal1 a substance that occurs naturally in some parts of ,india1 ,china1 and ,persia1 or by the addition of carbonate of soda to boracic acid1 a substance obtained from the volcanic districts of ,tuscany1 whence it is imported to this country1 and used in the manufacture of borax4 ,the element boron may be obtained by placing some pure boracic acid and some small bits of potassium in a tube together1 and applying the flame of a spirit-lamp1 a glow of heat takes place1 and when the tube is cold the potash may be washed away1 and the boron remains as a dark brownish powder somewhat resembling carbon4 ,m4 ,st4 ,claire ,deville and ,whler have lately made some important discoveries with respect to this element1 and disproved the statement that it is uncrystallizable4 ,their researches prove it to be producible under three forms and of various colours1 such as honey-yellow and garnet-red1 the crystals in some cases being like diamonds of the purest water--i4e41 limpid and transparent4 ,a new combination of aluminium and boron is stated to possess the most remarkable properties4 ,it is harder than the diamond1 and in the state of powder will cut and drill rubies1 and even the diamond itself1 with more facility than diamond powder4 ,deville and ,whler incline to the belief that the diamond is dimorphous1 and capable 7in conditions yet to be described7 of assuming the same forms as boron4 ,at a high temperature1 boron1 like titanium1 absorbs nitrogen only from the atmosphere1 and rejects the oxygen4 7,query1 may not some of those remarkably hard black diamonds prove to be boron87 ,,silicon4 ,symbol1 ,si2 combining proportion1 #ba4c4 ,the great ,berzelius was the first to obtain this element in #ahbc4 ,silicon in the pure state is a dark brown powder2 if ignited at a very high temperature it assumes a chocolate colour1 which is supposed to be the allotropic condition1 because it no longer burns when heated moderately in oxygen or air1 and is not attacked by hydrofluoric acid4 ,page #afb ,the most interesting combination of silicon is the teroxide called silicic acid1 silica 7,si,o#c74 ,silicon is next to oxygen so far as regards its plentifulness1 and is found in the state of silica in nearly every mineral1 but especially in rock crystal1 quartz1 flint1 sand1 jasper1 agate1 and tripoli4 ,it is largely used in the manufacture of glass1 and a most useful soluble glass is obtained by melting together in a crucible fifteen parts of sand1 ten parts of carbonate of potash1 and one part of charcoal4 ,cold water merely washes away the excess of alkali1 and after this is done the powdered soluble glass may be boiled with water in the proportion of one of the former with five of the latter1 when it gradually dissolves2 the solution may be evaporated to a thick pasty fluid1 which looks like jelly when cool1 and on exposure to the air in thin films changes to a transparent1 colourless1 brittle1 but not hard glass4 ,wood1 cotton1 and linen fabrics are rendered less combustible when coated with this glass1 which excludes the oxygen of the air1 and it has lately been employed to fill up the porous and capillary openings in stone exposed to the atmosphere1 and is stated to be very efficacious as a preservative of the stone in some cases4 ,,sulphur4 ,symbol1 ,s2 combining proportion1 #af4 ,sulphur1 like charcoal1 is of common occurrence in nature1 and is chiefly supplied from the volcanic districts of ,tuscany and ,sicily3 there is an abundance of this element in the ,united ,kingdom1 but then it is locked up in combination with iron1 copper1 and lead1 under the name of iron pyrites1 copper pyrites1 galena2 and whilst ,sicily and ,tuscany supply thousands of tons weight in the uncombined state1 it is not1 of course1 worth while to go through expensive operations at home for the separation of sulphur from the ores4 ,during the dispute between ,sicily and ,england1 several patents were secured for new and economical processes by which sulphur was obtained from various minerals2 and had this country been excluded from a supply of native sulphur1 no doubt some of these patents would now be in active operation4 ,it is almost possible to estimate the commercial prosperity of a country by the sulphur it consumes1 not1 happily1 by their warlike operations1 but in the manufacture of oil of vitriol or sulphuric acid1 which is the starting point of a great number of useful arts and manufactures4 ,first ,experiment4 ,some very curious results may be obtained by heating sulphur at certain temperatures2 in the ordinary state it is a pale yellow solid1 and when subjected to a temperature of #bbf ,fahr4 it melts to a brownish-yellow1 transparent1 thin fluid2 according to all preconceived notions of the properties of substances which liquify by an increase of heat1 it might be imagined that every additional degree of heat would only ,page #afc render the melted sulphur still more liquid1 but strange to say1 when it reaches a temperature of about #cbj ,fahr4 it changes red1 and thick like treacle2 and as the heat rises it becomes so tenacious1 that the ladle in which it is contained may be inverted1 and the sulphur will hardly flow out3 at about #dhb ,fahr4 it again becomes liquid1 but not so fluid as at the lower temperature4 ,if allowed to cool from #dhb ,fahr41 the above results are simply inverted2 the sulphur becomes thick1 again liquid1 and finally crystallizes in long1 thin1 rhombic prisms1 which are seen most perfectly by first allowing a crust of sulphur to form on the liquid portion1 and then having made two holes in this crust1 the sulphur is poured out1 when the remainder is found in the interior of the crucible crystallized in the form already mentioned4 ,sulphur takes fire in the air when exposed to a heat of about #efj ,fahr41 and burns with a pale blue flame2 and1 as already stated1 it may be poured from a considerable height on a still dark night1 and produces a continuous column of blue fire1 just like an unbroken current of electricity4 ,if the melted and burning sulphur is received into a vessel containing boiling water1 it is no longer yellow1 but assumes a curious allotropic state1 in which it is a reddish-brown1 transparent1 shapeless mass1 that may be easily kneaded and used for the purpose of taking casts of seals1 which become yellow in a few days1 and are found then to be hard and crystallized4 ,second ,experiment4 ,sulphur vapour1 in one sense1 may be regarded as a supporter of combustion3 if a clean ,florence oil-flask is filled with copper turnings1 and a little roughly-powdered sulphur sprinkled in1 and heat applied1 the copper glows with an intense heat1 and burning in the vapour of the sulphur1 produces a sulphuret of copper2 from this compound the sulphur may be again obtained by boiling the powdered sulphuret with weak nitric acid1 which oxidizes and dissolves the copper1 leaving the greater part of the sulphur behind1 which may be collected1 melted1 and burnt1 and will be found to display all the properties belonging to that element4 ,this experiment is a very good example of simple analysis2 and if the copper is weighed and likewise the combined sulphur1 a good notion may be formed of the principles of combining proportions4 ,third ,experiment4 ,a little sulphur burnt under a gas jar1 or in any convenient box 7a hat-box1 for instance71 produces sulphurous acid 7,,so#b71 which will bleach a wetted red rose or dahlia1 and many other flowers4 ,this gas is employed most extensively in bleaching straw1 and sundry woollen goods1 such as blankets and flannel1 and likewise silk1 and is perhaps one of the best disinfectants that can be employed2 when fever has been raging in the dwellings of the poor1 as in cottages1 c41 all metallic substances should be removed1 the doors and windows closed1 the bedding1 c41 well exposed1 and then a quantity of sulphur should be burnt in an old ,page #afd frying-pan placed on a brick1 taking care to avoid the chance of setting the place on fire2 after a few hours the doors and windows may be opened1 and the disinfectant will be found to have done its work cheaply and surely4 ,fourth ,experiment4 ,the presence of sulphur in various organic substances1 such as hair1 the white of egg1 and fibrine1 is easily detected by heating them in a solution of potash1 and adding acetate of lead as long as the precipitate formed is redissolved2 finally the solution must be heated to the boiling point1 when it instantly becomes black by the separation of sulphuret of lead4 ,fifth ,experiment4 ,sulphuric acid1 ,,ho1,,so#c1 or oil of vitriol1 is made in such enormous quantities that it is never worth while to attempt its preparation on a small scale4 ,in consequence of its great affinity for water1 many energetic changes are produced by its action4 ,oil of vitriol poured on some loaf sugar placed in a breakfast-cup with the addition of a dessert-spoonful of boiling water1 rapidly boils and deposits an enormous quantity of black charcoal4 ,if a word be written on a piece of white calico with dilute sulphuric acid1 and then rapidly and thoroughly washed out1 no visible change occurs2 but if the calico is exposed to heat1 so that the excess of water is driven off1 the remaining and now concentrated oil of vitriol attacks the calico1 and the word is indelibly printed in black by the decomposition of the fabric of cotton4 ,a very remarkable process has lately been introduced by ,mr4 ,warren de la ,rue1 by which paper is converted into a sort of tough parchment-like material1 called ametastine1 by the action of oil of vitriol and water of a certain fixed strength2 and any departure from the exact proportions destroys the toughness of the paper4 ,after the paper has been acted upon by the acid1 it becomes extremely tenacious1 and will support a considerable weight without breaking4 ,mr4 ,smee has used this ametastine in the construction of an hygrometer1 and states that it may save many a traveller from catching a severe rheumatism in a damp bed4 ,sixth ,experiment4 ,when the vapour of sulphur is passed over red-hot charcoal and the product carefully condensed1 a peculiar liquid is obtained1 called bisulphide of carbon 7,,cs#b71 which possesses a peculiar odour1 is extremely transparent and brilliant-looking1 and enjoys a high refractive power4 ,this liquid is used as a solvent for phosphorus and other substances1 and is extremely volatile and combustible1 and burns silently with a pale blue flame4 ,the combustion of its vapour1 mixed with certain gases1 offers a good example of the fact that slow burning may be a peaceful experiment1 whilst very rapid combustion often resolves itself into an explosion4 ,thus1 if a few drops of bisulphide of carbon are dropped into a narrow-mouthed dry quart bottle containing common air1 and flame applied1 the combustion takes place with rapidity1 a rushing or ,page #afe roaring sound being audible1 in consequence of the diffused vapour being supplied with more oxygen1 and burning more rapidly than it would do if simply consumed from a stick or glass rod wetted with the fluid4 ,a still greater rapidity of combustion is ensured by dropping some bisulphide of carbon into a long stout cylindrical jar1 fifteen inches long and three inches in diameter1 containing nitric oxide gas 7,,no#b72 when flame is applied the mixture burns with a bright flash and some noise1 and if burnt in a narrow mouthed bottle would most likely blow it to atoms4 ,the greatest rapidity of combustion1 and of course the loudest noise1 is obtained by shaking some bisulphide of carbon in a similar stout and strong cylindrical jar filled with oxygen gas1 but in this case the jar must be protected with a double cylinder of stout wire gauze2 it does not always break1 but if it is blown to fragments each particle becomes a lancet-shaped piece of glass1 which is capable of producing the most dangerous wounds4 7,fig4 #aeb47 ,illustration3 ,fig4 #aeb4 ,a4 ,air and bisulphide of carbon4 ,b4 ,nitric oxide and ditto4 ,c4 ,oxygen and ditto4 ,d ,d4 ,stout cylinder of double wire gauze1 open top and bottom4 ,,selenium4 ,selenium 7,greek3 seln1 the ,moon,b72 symbol1 ,se2 combining proportion1 #ci4e4 ,this new metallic element is allied to sulphur1 and is a species of chemical curiosity1 being found in minute quantities in various minerals2 it may be melted and cast into any form4 ,medallions of the discoverer 7,berzelius7 of selenium1 in little cases1 are imported from ,germany1 for the cabinets of the curious4 ,footnote ,b3 ,called selenium on account of its strong analogy to the metal tellurium 7tellus1 the earth74 ,page #aff ,,phosphorus4 ,phosphorus 7,greek3 phs1 light2 ,greek3 pherein1 to bear2 symbol1 ,p2 combining proportion1 #cb47 ,monsieur ,salverte1 in his work on the ,occult ,sciences of the ,ancients1 quotes a remarkable story respecting the probable discovery of the nature of phosphorus in #agfa3--;,a ,prince ,san ,severo1 at ,naples1 cultivated chemistry with some success2 he had1 for example1 the secret of penetrating marble with colour1 so that each slab sawed from the block presented a repetition of the figure imprinted on its external surface4 ,in #agfa1 he exposed some human skulls to the action of different reagents1 and then to the heat of a glass furnace1 but paying so little attention to his manner of proceeding1 that he acknowledged he did not expect to arrive a second time at the same result4 ,from the product he obtained a vapour1 or rather a gas was evolved1 which kindling at the approach of a light1 burned for several months without the matter appearing to die or diminish in weight4 ,san ,severo thought he had found1 the impossible secret of the inextinguishable lamp1 but he would not divulge his process1 for fear that the vault in which were interred the princes of his family should lose the unique privilege with which he expected to enrich it1 of being illuminated with a perpetual lamp4 ,had he acted like a philosopher of the present day1 ,san ,severo would have attached his name to the important discovery of the existence of phosphorus in the bones1 and made public the process by which it might be obtained4 ,this element1 formerly sold at four or five shillings the ounce1 has now fallen so much in price1 from the greater demand and larger production1 that it may be bought for a few shillings the pound1 and is imported in tin cases in large quantities from ,germany4 ,it was discovered about two hundred years ago by ,brandt1 a merchant of ,hamburg1 and may be prepared on a small scale by distilling at a red heat phosphoric acid previously fused with one-fourth of its weight of powdered charcoal4 ,first ,experiment4 ,phosphorus1 when pure1 is without taste or colour1 but generally of a very pale buff-colour1 and semi-transparent2 it is extremely combustible1 and is usually preserved under the surface of water2 when perfectly dry1 a thin slice will take fire at #fj ,fah41 and burns with great brilliancy4 ,considering the heat produced during the combustion of phosphorus1 it might be thought that it would infallibly set fire to any ordinary combustible1 such as paper or wood1 but this is not the case when phosphorus is employed by itself1 as may be proved by the following experiment4 ,cut five very small pieces of phosphorus1 and place them like the five of diamonds on a sheet of cartridge-paper laid upon the table1 set the bits of phosphorus on fire1 when they will be rapidly burnt away ,page #afg leaving only five black spots1 but not firing the paper1 as would be the case if some red-hot coals or charcoal were placed in the same position4 ,the cause is very simple4 ,phosphorus in burning produces phosphoric acid1 which is an anti-combustible1 and coats the surface of the paper round the spot where the combustion occurs1 and acting as a kind of glaze or glass1 excludes the oxygen of the air1 and prevents the fire spreading4 ,if some powdered sulphur is sprinkled round the spot where the bit of phosphorus is to be burnt1 the case is very different2 the heat melts and sets fire to the sulphur1 which being uncoated with the phosphoric acid1 communicates to the paper2 and it is on this principle that lucifer-matches can be used as instantaneous lights4 ,the tip of the wood of which they are composed is first dipped in sulphur1 and then the phosphorus composition made of gum1 chlorate of potash1 vermilion1 and phosphorus1 is placed over it2 and if the latter were used alone without the sulphur1 not one match in a hundred would take fire properly4 ,second ,experiment4 ,common phosphorus is perfectly and rapidly dissolved by bisulphide of carbon4 ,the solution must be carefully preserved1 as it is a liquid combustible1 which takes fire spontaneously after the bisulphide of carbon evaporates2 so that wherever it is dropped1 a flame1 arising from the spontaneous combustion of the finely-divided phosphorus1 is sure to be produced4 ,this liquid was recommended many years ago to the ,government for the purpose of setting sails of ships or other combustible matter on fire4 ,the solution of phosphorus alone did not answer the purpose1 as already explained in the first experiment2 but when wax was dissolved with the phosphorus1 it then became a most dangerous fluid1 which it was recommended should be used in shells1 and discharged from a mortar or howitzer in the ordinary manner4 ,dr4 ,lyon ,playfair was the first to make this proposed application of the solution1 and it has since1 we believe1 been recommended by ,captain ,norton in his liquid-fire shells4 ,third ,experiment4 ,one of the most curious facts in connexion with phosphorus1 is its assumption of the allotropic state in what is termed amorphous 7shapeless7 or red phosphorus4 ,this substance1 when handled for the first time1 might be mistaken for a lump of badly-made ,venetian red4 ,there is no risk of its taking fire like the common phosphorus1 and it does not 7according to ,schrtter1 of ,berlin1 who discovered this peculiar condition7 exhale those fumes which are so prejudicial to the lucifer-match makers4 ,when the vapour of common phosphorus is continually inhaled1 it is said to cause a peculiar and disgusting disease1 which terminates in the destruction of the jaw-bone2 whilst the bones in other parts of the body become brittle1 and arm-bones thus affected are fractured with the slightest blow4 ,the difference between common and red phosphorus is well shown first1 ,page #afh by placing a few small pieces of both kinds in separate bottles or vials containing bisulphide of carbon2 the common phosphorus1 as already explained1 quickly dissolves in the liquid1 and if poured on a sheet of paper1 and hung up1 is soon on fire2 whilst the red variety is wholly unaffected1 and if the bisulphide of carbon is poured off on to paper1 it merely evaporates1 and no combustion occurs4 ,the similarity in composition1 though not in outward form1 is further shown by filling two jars with oxygen gas1 and having provided two deflagrating spoons1 some common phosphorus is placed in one1 and red phosphorus in the other2 a wire1 gently heated by dipping it into some boiling water1 is now applied to the former1 which immediately takes fire1 and may be plunged into the jar of oxygen gas1 when it burns with the usual brilliancy4 ,the red phosphorus1 however1 must be brought to a much higher temperature 7#ejj ,fah47 before it will even shine in the dark1 and then with a still further increase of heat it takes fire1 and on being placed in the other jar of oxygen burns up much more slowly than the yellow phosphorus1 but at last exhibits that brilliant flash of light which is so characteristic of the combustion of phosphorus in oxygen4 ,the amorphous or red phosphorus is employed in the manufacture of safety chemical matches1 and ,m4 ,a4 ,meunons has secured a patent in ,england for an improvement in lucifer matches1 with a view to obviate the risks of accidental ignition4 ,to attain this end the matches are first cut by a machine from cubes of wood1 the cut being stopped at a short distance from the end of each cube1 so as to leave the lower extremities adherent4 ,the upper or free extremity of each packet of splints thus formed being coated with wax or sulphur1 is dipped in one of the following preparations3--,chlorate of potash1 two parts2 pulverized charcoal1 one part2 umber1 one part2 or1 chlorate of potash1 sulphur1 and umber1 in equal parts1 thoroughly mixed with glue4 ,the opposite extremity or cut of each packet is then painted over with amorphous phosphorus blended with size1 so that on separating the matches the phosphorus is only found on the top of each4 ,the matches thus prepared are ignited by breaking off a small piece of the phosphorised end and rubbing it on the opposite extremity covered with the inflammable preparation4 ,loud exploding and dangerous lucifers were formerly made by dipping bundles of matches1 previously coated with sulphur at the tips1 into a thick solution of gum1 at a temperature of #ajd ,fahr41 coloured with smalt or red lead1 in which was dissolved a certain proportion of chlorate of potash1 and also containing finely divided particles of phosphorus obtained by the constant stirring and rubbing of the materials in a mortar4 ,when dry the matches exploded if rubbed against a gritty surface1 and there was always a risk of a fragment flying off and entering the eye4 ,to obviate this danger1 silent or noiseless lucifer matches were invented1 and the composition used 7according to ,bttger7 is as follows3--,gum arabic1 #af parts by weight2 phosphorus1 #i parts2 nitre1 #ad parts2 powdered black oxide of manganese1 #af parts4 ,the above ingredients are worked up in a mortar with water1 at #ajd ,fahr41 and the matches previously tipped with sulphur are dipped therein and afterwards dried4 ,page #afi ,fourth ,experiment4 ,the combustion of phosphorus under water is easily demonstrated by placing some ordinary stick phosphorus in a metallic cup1 and then plunging it rapidly under the surface of boiling water4 ,if a jet of oxygen gas is now directed upon the liquid phosphorus1 it burns with great brilliancy4 ,when the oxygen escapes too rapidly from the jet1 it causes some small particles to be thrown out of the water1 so that it is advisable to defend the face with a sheet of wire gauze held a few inches above the glass whilst the experiment is being conducted4 7,fig4 #aec47 ,illustration3 ,fig4 #aec4 ,a ,a4 ,finger-glass of boiling water containing a metallic cup with melted phosphorus4 ,c4 ,jet of oxygen gas4 ,d ,d4 ,sheet of wire gauze4 ,fifth ,experiment4 ,phosphorus burns and emits beautiful flashes of light in the presence of the gas called peroxide of chlorine 7,cl,o#d71 which must be very carefully generated under the surface of water by first placing some cut phosphorus and chlorate of potash at the bottom of a long and stout cylindrical glass nearly full of water2 sulphuric acid is then conveyed to the chlorate of potash by means of a syphon1 the end of which must be drawn out to a small opening1 or else the oil of vitriol will descend too rapidly1 and the glass will be cracked by the heat4 ,immediately the peroxide of chlorine comes in contact with the phosphorus it explodes1 and passes again to its original elements1 oxygen and chlorine4 ,these bubbles envelope minute particles of phosphorus1 which rapidly ascend1 like water-spiders1 to the surface1 and burn as they pass upwards1 producing a continual series of sparks of fire1 which have an extremely pretty effect4 7,fig4 #aed47 ,the syphon is of course first filled with water1 and as that is displaced1 the oil of vitriol takes its place4 ,illustration3 ,fig4 #aed4 ,a ,a4 ,tall glass nearly full of water2 at the bottom are the chlorate of potash and phosphorus4 ,b4 ,wolfe's bottle and syphon1 conveying the oil of vitriol to bottom of ,a ,a4 ,page #agj ,sixth ,experiment4 ,if a little phosphorus is placed in a small copper boiler1 and the steam allowed to escape from a jet1 it is observed to be luminous1 in consequence of a minute portion of phosphorus being carried up mechanically with the steam4 ,the same fact is shown very prettily by boiling water in a flask containing some phosphorus4 ,seventh ,experiment4 ,phosphorus explodes violently when rubbed with a little chlorate of potash1 and in order to perform this experiment safely1 it should be made in a strong iron mortar1 the pestle of which must be surrounded with a large circle of cardboard and wire gauze2 so that when it is brought down upon the phosphorus and chlorate of potash1 any particles that may fly out are detained by the shield4 ,without this precaution the experiment is one of the most dangerous that can be made4 7,fig4 #aee47 ,illustration3 ,fig4 #aee4 ,a4 ,the iron mortar containing the phosphorus and chlorate of potash4 ,b4 ,the pestle1 with the shield1 ,c ,c1 composed of a circle of wire gauze1 covered with one of cardboard4 ,eighth ,experiment4 ,phosphuretted hydrogen owes its property of spontaneous combustion to the presence of the vapour of a liquid1 phosphide of hydrogen 7,,ph#b71 which may be prepared by placing some phosphide of calcium into a flask with water heated to a temperature of #adj ,fah41 and conveying the gas into a ,u-shaped tube surrounded with a mixture of ice and salt4 ,the liquid obtained is colourless1 and must be preserved from contact with air1 as it takes fire spontaneously directly it is exposed to the atmosphere4 7,fig4 #aef47 ,illustration3 ,fig4 #aef4 ,a4 ,the flask containing the phosphide of calcium and water1 and placed in a water-bath heated to #adj ,fah4 ,b4 ,bent tube conveying the gas to ,c ,c1 the ,u-shaped tube1 to which it is attached by india-rubber tubing1 ,c ,c4 ,the ,u-shaped tube1 surrounded with a freezing mixture4 ,d ,d4 ,bent tube1 passing into a cup of water to prevent contact with air4 ,page #aga ,ninth ,experiment4 ,phosphide of calcium is quickly prepared by placing some small pieces of lime in a crucible and making them red-hot2 if lumps of dry phosphorus are thrown into the crucible1 and the cover placed on quickly1 and immediately after the phosphorus1 the latter unites with the calcium1 and forms a brown substance which produces gaseous phosphide of hydrogen 7,,ph#c7 when placed in water1 and the gas takes fire spontaneously when it comes in contact with the air4 ,tenth ,experiment4 ,phosphorus placed in a retort with a tolerably strong solution of potash1 and a small quantity of ether1 affords a large quantity of phosphide of hydrogen 7commonly called phosphuretted hydrogen7 when boiled4 ,the neck of the retort must dip into a basin of water1 and the object of the ether is to prevent the combustion of the first bubbles of gas inside the retort1 which by their explosion would probably break the glass4 ,if the neck of the retort is kept under water in which potash is dissolved1 the gas may be generated for many days at pleasure1 although it is not a desirable experiment to renew too often1 on account of the disagreeable odour produced4 7,fig4 #aeg47 ,illustration3 ,fig4 #aeg4 ,a retort containing the phosphorus1 water1 potash1 and ether4 ,b4 ,neck dipping into a basin of water4 ,c4 ,the gas burning1 and producing beautiful rings of smoke4 ,eleventh ,experiment4 ,when a jar of oxygen is held over the neck of the retort generating the phosphuretted hydrogen1 a bright flash of light and explosion are observed2 and if the experiment is performed in a darkened room1 it is just like a sudden flash of lightning4 ,a bottle of chlorine held over the neck ,page #agb of the retort1 and dipping of course in the water of the basin1 produces a green flame every time the bubble of gas passes into it4 ,that curious appearance of light1 sometimes seen in marshy districts1 called will-o'-the-wisp1 is supposed to be due to the escape1 from decomposing matter1 of bubbles of hydrogen1 nitrogen1 c41 through which the spontaneously inflammable phosphide of hydrogen is diffused4 ,at a place called ,dead ,man's ,island1 near ,sheerness1 magnificent effects of this kind are sometimes apparent when the mud banks are accidentally stirred at night by a boat-hook4 ,a credible observer says1 he once saw there a flash of yellowish-green light1 accompanied with noise1 about thirty feet in height4 ,the apparent height might be due to the duration of the impression of the flash on the eye1 as the light from the burning phosphuretted hydrogen ascended rapidly upwards4 ,the source of this gas appears to be due to the fact1 that during the time some ,russian ships were watched by the ,brest fleet1 a number of the sailors died of cholera1 and were buried in the banks2 the decomposition of the bone containing phosphorus would account for the appearance of light already described4 ,with the discussion of some of the most interesting properties of the thirteen non-metallic elements we take leave of the subject of chemistry1 reserving the consideration of the metals for another popular juvenile work1 of which they will form the subject4 ,in answer to the oft-repeated question1 ,where can ,i get the things for the experiments8 it may be stated that every kind of glass vessel and the chemicals mentioned in this chapter1 can be procured either of ,messrs4 ,simpson1 ,maule1 and ,co41 ,kennington1 or of ,griffin and ,co41 ,bunhill-row1 or ,bolton and ,co41 ,high ,holborn4 ,illustration3 ,fig4 #aeh4 ,will-o'-the-wisp4 ,page #agc ,,chapter ,,xiii4 ,,frictional ,,electricity4 ,illustration3 ,fig4 #aei4 ,franklin and his kite4 ,of all the agents with which man is acquainted1 not one can afford a greater source of wonderment to the ignorant1 of meditation to the learned1 than the effects of that marvellous force pervading all matter called electricity4 ,we look at matter endowed with life1 and matter wanting this divine gift1 with some degree of interest1 depending on our various tastes and occupations2 we know at a glance a bird1 a beast1 or a fish2 we observe with pleasure and admiration the wonderful changes of nature1 and know that a few seeds thrown into the broken clods and well-tilled earth may become either the waving1 golden corn-field or in time may grow from the tender little shrub to the stately forest-tree2 we know all these things because they belong to the visible world1 and are continually passing before our eyes3 but in looking at the visible1 we must not forget and ignore the invisible4 ,it may with truth be ,page #agd stated that the greatest powers of nature are all concealed1 and if any truth would lead us from ,nature to ,nature's ,god1 it is the fact that no visible1 solid1 tangible agent can work with so much force and power as invisible electricity4 ,many centuries passed away since the commencement of the ,christian era1 before the human mind was prepared to appreciate this great power of nature2 other forces had claimed attention1 and the difference in the presence or absence of two of the imponderable agents1 heat and light1 as derived from the sun1 in the effects of the change of the seasons1 and other common facts1 had led philosophers to speculate early upon their nature2 but electricity1 from its peculiar properties1 long escaped observation1 and it was not until the beginning of the eighteenth century 7about #agcj7 that any material facts had been discovered in this science1 when ,mr4 ,stephen ,grey1 a pensioner of the ,charterhouse1 discovered what he termed electrics and non-electrics1 and also the use of insulating materials1 such as silk1 resin1 glass1 hair1 c42 and it is obvious that1 until the latter fact was discovered1 the science would remain in abeyance1 because there would be no mode of preserving the electrical excitement in the absence of non-conductors of this force4 ,the year #agej was remarkable for ,volta's discoveries and ,dr4 ,franklin's identification of the electricity of the machine with the stupendous effects of the thunderstorm4 ,sir ,humphry ,davy1 in #ahjj1 with his commanding genius1 threw fresh light upon the already numerous electrical effects discovered4 ,in #ahba1 ,faraday commenced his studies in this branch of philosophy2 which he has since so diligently followed up1 that he has been for some years1 and is still the first electrician of the age4 ,from the commencement of the present century1 discoveries have succeeded each other in regular order and with the most amazing results2 and now electricity is regularly employed as a money-getting agent in the process of the electrotype and electro-silvering and gilding2 also in the electric telegraph2 and in a few years we may possibly see it commonly employed as a source of artificial light4 ,the nature of electricity1 says ,turner1 like that of heat1 is at present involved in obscurity4 ,both these principles1 if really material1 are so light1 subtle1 and diffuse1 that it has hitherto been found impossible to recognise in them the ordinary characteristics of matter2 and therefore electric phenomena may be referred1 not to the agency of a specific substance1 but to some property or state of common matter1 just as sound and light are produced by a vibrating medium4 ,but the effects of electricity are so similar to those of a mechanical agent1 it appears so distinctly to emanate from substances which contain it in excess1 and rends asunder all obstacles in its course so exactly like a body in rapid motion1 that the impression of its existence as a distinct material substance sui generis forces itself irresistibly on the mind4 ,all nations1 accordingly1 have spontaneously concurred in regarding electricity as a material principle2 and scientific men give a preference to the same view1 because it offers an easy explanation of phenomena1 and suggests a natural language intelligible to all4 ,page #age ,there are five well-ascertained sources of electricity1 and three which are considered to be uncertain4 ,the five sources are friction1 chemical action1 heat1 magnetism1 peculiar animal organisms4 ,the three uncertain sources are contact1 evaporation1 and the solar rays4 ,first ,experiment4 ,a stick of sealing-wax or a bit of glass tube1 perfectly dry1 rubbed against a warm piece of flannel1 has elicited upon its surface a new power1 which will attract bits of paper1 straw1 or other light materials2 and after these substances are endowed with the same force1 a repellent action takes place1 and they fly off4 ,one of the most convenient arrangements for making experiments with the attractive and repellent powers of electricity is to fix with shell-lac varnish round discs of gilt paper1 of the size of a half-crown1 at each end of a long straw that is supported about the centre with a silk thread1 which may hang from the ceiling or any other convenient support4 7,fig4 #afj47 ,illustration3 ,fig4 #afj4 ,a4 ,the glass pillar support4 ,b4 ,straw with discs1 hanging by a silk thread4 ,the varnish is easily prepared by placing four or eight ounces of shell-lac in a bottle1 and pouring enough pyroxylic spirit 7commonly termed wood naphtha7 upon the lac to cover it4 ,after a short time1 and by agitation1 solution takes place4 ,in a variety of ways friction is proved to be a source of electricity1 and forms a distinct branch of the science1 under the name of frictional electricity4 ,second ,experiment4 ,the nature of chemical action has been already explained1 and is alluded to here as a source of electricity of which the proof is very simple4 ,a piece of copper and a similar-sized plate of zinc have attached to them copper wires2 these plates are placed opposite to1 but do not touch each other1 in a vessel containing water acidulated with a small quantity of sulphuric acid4 ,when the wires are brought in contact1 a current of electricity circulates through the arrangement1 but has no power to attract bits of paper1 straw1 c4 ,in order to ascertain whether the current of electricity passes or not1 a piece of covered copper wire is bent several times round a magnetic needle1 so that it has freedom of motion inside the core or hollow formed by twisting the copper wire4 ,this arrangement1 properly constructed1 is called the galvanometer ,page #agf needle1 and is invaluable as a means of ascertaining the passage of electricity derived from chemical action4 7,fig4 #afa47 ,illustration3 ,fig4 #afa4 ,a4 ,the galvanometer needle4 ,b4 ,vessel containing weak acid and the zinc and copper plates4 ,the arrows show the path of the electric current4 ,when the wires leading from the metal plates are connected with the extremities of the coil in the galvanometer1 the needle is deflected or pushed aside to the right hand or to the left1 according to the direction of the current4 ,third ,experiment4 ,the third source of electricity is heat1 and the effect of this agent is well shown by twisting together a piece of platinum and silver wire1 so as to form one length4 ,if the silver end is attached to any screw of the galvanometer1 and the platinum end to the second screw1 no movement of the magnetic needle takes place until the heat of a spirit-lamp is applied for a moment to the point of juncture between the silver and platinum wires1 when the magnetic needle is immediately deflected4 ,illustration3 ,fig4 #afb4 ,a4 ,the galvanometer needle1 with wires attached4 ,s1 ,s4 ,silver wire joined to ,p1 ,p1 the platinum wire4 ,the heat of the spirit-lamp is applied at the point of juncture1 4 ,fourth ,experiment4 ,the fourth source of electricity--viz41 magnetism--requires a somewhat more complicated arrangement2 and a most delicate galvanometer needle must be provided1 to which is attached the extremities of a long spiral coil of copper wire covered with cotton or silk4 ,every time a bar magnet is introduced inside the coil1 so that the conducting wire cuts the magnetic curves1 a deflection of the galvanometer needle takes place1 ,page #agg and the same effect is produced on the withdrawal of the magnet1 the needle being deflected in the opposite direction4 ,the magnetic spark can be obtained by employing a magnet of sufficient power2 and the arrangement for this purpose is very simple4 ,a cylinder of soft iron is provided1 and round its centre are wound a few feet of covered thin copper wire1 one end of which is terminated with a copper disc well amalgamated1 and the other end1 after being properly cleaned and coated with mercury1 is brought into contact with the disc4 ,directly this cylinder is laid across the poles of the magnet1 and as quickly removed1 the point and disc1 from the elasticity of the former1 separate for the moment1 the contact is broken between the point and disc1 and a brilliant but tiny spark is apparent4 ,illustration3 ,fig4 #afc4 ,a ,b4 ,horse-shoe magnet4 ,c4 ,cylinder of soft iron4 ,d4 ,coil of copper wire and contact breaker4 ,fifth ,experiment4 ,the fifth mode of procuring electricity would require the assistance of an electrical eel1 a fine specimen of which 7forty inches in length7 was exhibited at the ,adelaide ,gallery some years ago4 ,various experiments were made with this animal1 and the author had the pleasure of witnessing all the ordinary phenomena of frictional electricity1 illustrated by ,dr4 ,faraday1 with the assistance of the animal electricity derived from this curious creature4 ,recent experiments have1 however1 proved that the electric current is induced through the agency of the nervous ,page #agh system4 ,this important fact has been communicated by ,m4 ,dubois-,raymond1 whose experiment is thus recorded3--,a cylinder of wood is firmly fixed against the edge of a table2 two vessels filled with salt and water are placed on the table1 in such a position that a person grasping the cylinder may1 at the same time1 insert the fore-finger of each hand in the water4 ,each vessel contains a metallic plate1 and communicates1 by two wires1 with an extremely sensitive galvanometer4 ,in the instrument employed by ,m4 ,dubois-,raymond1 the wire is about #c miles in length4 ,the apparatus being thus arranged1 the experimenter grasps the cylinder of wood firmly with both hands1 at the same time dipping the fore-finger of each hand in the saline water4 ,the needle of the galvanometer remains undisturbed2 the electric currents passing by the nerves of each arm1 and being of the same force1 neutralize each other4 ,now1 if the experimenter grasp with energy the cylinder of wood with the right hand1 the left hand remaining relaxed and free1 immediately the needle will move from west to south1 and describe an angle of #cj1 #dj1 and even #ej2 on relaxing the grasp1 the needle will return to its original position4 ,the experiment may be reversed by employing the left arm1 and leaving the right arm free3 the needle will1 in this case1 be deflected from west to north4 ,the reversing of the action of the needle proves the influence of the nervous force4 ,the conditions1 it may be added1 essential to the success of the experiment are3 #ast1 ,great muscular and nervous energy2 #bnd1 ,the contraction of only one arm at a time2 #crd1 ,dryness and cleanliness of skin2 and #dth1 ,freedom from any kind of wound on the immersed part4 ,sixth ,experiment4 ,in making electrical experiments of the simplest kind1 it soon becomes apparent that certain substances1 such as glass1 sealing-wax1 c41 retain the condition of electrical excitement2 whilst other bodies1 and especially the metals1 seem wholly incapable of electrical excitation3 hence the classification of bodies into conductors and non-conductors of electricity4 ,this arrangement is not strictly correct1 because no substance can be regarded as absolutely a conductor1 or vice vers4 ,it is better to consider these terms as meaning the two extremes of a long chain of intermediate links1 which pass by insensible gradations the one into the other4 ,in the manufacture of electrical apparatus1 glass is of course largely employed1 and this substance1 with brass and wood1 constitute the usual materials4 ,one of the most instructive pieces of apparatus is the electroscope1 which can be made with a gas jar1 a cork1 a piece of glass tube1 brass wire and ball1 or a flat disc of brass1 with some ,dutch metal1 or still better1 gold leaf4 ,the latter is first cut into strips by retaining the leaf between a sheet of well-glazed paper and cutting through the paper and the copper or gold leaf1 otherwise it would be impossible to cut the metal1 on account of its excessive thinness1 except with a gilder's knife and cushion4 ,the cork is next fitted to the gas jar1 and perforated with a hole to admit the glass tube1 which must be thoroughly dry1 and ,page #agi is best coated both inside and out with the shell-lac varnish described at page #age4 ,some dry silk is wound round the brass wire1 so that it remains fixed and upright in the glass tube1 the end outside the jar having a ball1 or still better1 a flat disc of brass attached1 and the other extremity being split so as to act like a pair of forceps1 to retain a piece of card to which the gold leaves are attached4 ,by removing the cork1 tube1 and brass wire bodily from the neck of the gas jar1 and then in a perfectly still atmosphere carefully bringing the card1 slightly wetted with gum at the extremity1 on two of the cut gold leaves1 they may be stuck on1 and the whole is again arranged inside the dry gas jar1 and forms the important instrument called the electroscope4 7,fig4 #afd47 ,with the help of this arrangement1 a number of highly instructive experiments are performed4 ,illustration3 ,fig4 #afd4 ,a4 ,the brass wire1 with flat disc outside1 and forceps holding gold leaf ,b inside the jar4 ,c ,c4 ,the glass tube4 ,seventh ,experiment4 ,first1 the difference between conductors and non-conductors is admirably shown by rubbing a bit of sealing-wax against a piece of woollen cloth or flannel2 on bringing the wax to the brass disc of the electroscope the gold leaves no longer hang quietly side by side1 but stand out and repel each other1 in obedience to the law that bodies similarly electrified repel each other4 ,if the brass cap is touched whilst the leaves are in this electrical state1 they fall again to their original position1 showing that sealing-wax1 after being excited1 retains its electrical condition1 as also the gold leaves1 because they are supported on glass1 or what is termed insulated--i4e41 cut off from conducting communication with surrounding objects4 ,when1 however1 the sealing-wax is passed through a damp hand1 or the brass disc of the electroscope touched1 the electricity is conveyed away to the earth1 because the human body is a conductor of electricity4 ,eighth ,experiment4 ,when a brass wire is rubbed and brought to the electroscope1 the leaves do not move1 in consequence of the electricity passing away to the earth through the body as fast as it is generated3 it is just like pouring water into a leaky cistern2 but if the brass wire is tied to a long stick of sealing-wax1 and this latter held in the hand whilst the wire is rubbed with a bit of flannel1 then the gold leaves of the electroscope are affected1 on account of the insulation of the metal1 as every substance which can be rubbed 7even fluids1 as water7 produces electricity4 ,page #ahj ,ninth ,experiment4 ,an insulating stool is merely a piece of strong square board1 supported on glass legs1 which should be well varnished4 ,if the assistant stands on this stool and touches the disc of the electroscope1 no movement of the leaves takes place until his coat is briskly struck with a piece of dry silk or skin1 when the usual repulsion occurs4 ,illustration3 ,fig4 #afe4 ,assistant standing on the insulating stool and touching the disc of the electroscope whilst being struck with a dry handkerchief4 ,tenth ,experiment4 ,if a little powdered chalk is placed inside a pair of bellows1 and then forcibly ejected on to the disc of the electroscope1 the friction of the particles of chalk against the inside of the nozzle of the bellows and against the disc of the instrument soon liberates sufficient electricity to cause the gold leaves to stand out and repel each other4 ,eleventh ,experiment4 ,whilst the leaves of the electroscope are repelled from each other by the application of a bit of rubbed sealing-wax1 they may be again caused to approach each other on bringing a dry glass tube previously rubbed with a silk-handkerchief2 because the electricity obtained from sealing-wax is different from that procured from glass3 the former is called resinous or negative electricity1 the latter positive or vitreous electricity4 ,either1 separately1 is repulsive of its own particles1 but attractive of the other4 ,page #aha ,no electrical excitation can occur without the separation of these two curious states of electricity1 and electrical quiescence takes place when the two electricities are brought together2 hence the fall of the gold leaves repelled by rubbed wax when the excited glass is brought towards the disc of the electroscope4 ,this experiment may be reversed by repelling the leaves first with the excited glass1 and then bringing the rubbed wax1 when the same effect takes place4 ,twelfth ,experiment4 ,to show the important elementary truth1 that in all cases of electrical excitation the two kinds of electricity are generated1 take a dry roll of flannel1 and holding it as lightly as possible1 rub it against a bit of wax4 ,if the flannel is brought to the electroscope1 the leaves repel each other1 and they immediately fall when the wax is now approached1 because the flannel is in the positive or vitreous state of electricity1 whilst the sealing-wax is in the negative or resinous condition4 ,thirteenth ,experiment4 ,any kind of friction generates electricity4 ,a little roll of brimstone placed in a dry mortar and powdered1 and then thrown on to the electroscope1 quickly causes the repulsion of the leaves4 ,fourteenth ,experiment4 ,a sheet of dry brown paper laid on a flat surface1 and vigorously rubbed with a piece of india-rubber1 produces so much electricity that sparks and flashes of light are apparent in a dark room when it is lifted from the table2 and it affects the leaves of the electroscope very powerfully1 so much so that care must be taken to apply it very carefully to the disc1 or the violence of the repulsion may cause the fracture of the gold leaves1 and then a great deal of time is wasted before they can be put on again4 ,fifteenth ,experiment4 ,a dry wig or bunch of horse-hair when combed becomes electrical1 and likewise affects the leaves of the electroscope4 ,sixteenth ,experiment4 ,two dry silk ribbons1 the one white and the other black1 passed rapidly together through the fingers1 exhibit sparks and flashes of light when drawn asunder1 and also cause the gold leaves to repel each other4 ,seventeenth ,experiment4 ,much instructive amusement is afforded by testing the gold leaves when separated from each other during either of the former experiments1 ,page #ahb with an excited piece of sealing-wax4 ,if the electricity produced is negative1 they repel each other further when the excited wax is approached2 if positive1 they fall when the excited wax is brought near them4 ,eighteenth ,experiment4 ,when fresh1 dry1 ground coffee is received on to the disc of the electroscope1 as it falls from the mill1 powerful electrical excitation is displayed1 and this is sometimes so apparent1 that the particles cling around the lower part of the mill or to the sides of the cup or basin held to catch it4 ,nineteenth ,experiment4 ,after playing a tune on a violin1 hold the bow 7well rosined7 to the electroscope1 when the usual divergence of the leaves will be apparent4 ,twentieth ,experiment4 ,cut some chips from a piece of wood with a knife attached to a glass handle1 and as they fall on to the electroscope the leaves are repelled4 ,twenty-first ,experiment4 ,warm a piece of bombazine by the fire and then draw out some of the threads 7which are of two kinds--viz41 silk and wool71 and place them on the electroscope1 when divergence of the leaves immediately takes place4 ,twenty-second ,experiment4 ,put upon the same leg a worsted stocking and over that a silk one1 if the latter is now quickly rubbed all over with a dry hand and near the fire1 and then suddenly slipped off1 the sides repel each other1 and the silk stocking retains very much the same shape as if the leg still remained in it1 and of course collapses as the electricity passes away4 ,twenty-third ,experiment4 ,electrical machines consist only in the better arrangement of larger pieces of glass and a more convenient mechanical contrivance for rubbing them1 and are of two kinds--viz41 the cylinder and plate machines2 it is usual to give directions for the manufacture of an electrical machine from a common bottle1 and doubtless such rude instruments have been made1 but as ,messrs4 ,elliott ,brothers1 of #cj1 ,strand1 now supply excellent small machines at a very low cost1 it is hardly worth while to incur even a small expense for an instrument that must at the best be a very imperfect one and frequently out of order4 7,fig4 #aff47 ,page #ahc ,illustration3 ,fig4 #aff4 ,a cylinder electrical machine4 ,illustration3 ,fig4 #afg4 ,the ordinary plate electrical machine4 ,plate machines are somewhat more expensive than cylinder ones1 but at the same time are more quickly prepared for experiments1 and ,mr4 ,hearder1 of ,plymouth1 states1 that the secret in obtaining the greatest amount of electricity from a cylinder machine1 is to keep the inside of the glass absolutely clean1 dry1 and free from dust4 ,sometimes the glass of which electrical machines are made is wholly unfit for electrical ,page #ahd purposes1 in consequence of the decomposition of the surface from imperfect manufacture and the liberation of the alkali4 7,figs4 #afg1 #afh47 ,illustration3 ,fig4 #afh4 ,woodward's double plate electrical machine1 giving a much larger quantity of electricity than ,fig4 #afg4 ,twenty-fourth ,experiment4 ,cylinder and plate machines are furnished with proper rubbers1 and before using the instrument it is usual to remove them1 and after carefully cleaning the glass with a dry silk handkerchief before a fire1 the rubbers are scraped with a paper-knife to remove the old amalgam1 and fresh applied by first melting the end of a tallow candle slightly1 and after passing this over the rubber1 the finely powdered amalgam is now dusted on to it4 ,electrical amalgam is prepared by fusing one part of zinc with one of tin1 and then agitating the liquid mass with two parts of hot mercury placed in a wooden box2 when cold it should be carefully powdered and kept in a well-stoppered bottle for use4 ,when the amalgam has been applied1 the rubbers are again screwed in their places1 and the machine when turned 7if the atmosphere is tolerably dry7 will emit an abundance of bright sparks4 ,twenty-fifth ,experiment4 ,attraction and repulsion are shown on a larger scale1 with the assistance of electrical machines1 by placing a fishing rod 7the last joint of ,page #ahe which is made of glass7 in an erect position1 and attaching to the extremity a long tassel of paper from which a thin wire passes to the prime conductor of the electrical machine2 on turning the instrument1 the strips of paper all stand out and repel each other4 7,fig4 #afi47 ,illustration3 ,fig4 #afi4 ,a ,a4 ,the glass joint of the fishing-rod1 from which the last joint1 carrying the paper tassel1 ,b1 projects4 ,c4 ,the electrical machine4 ,illustration3 ,fig4 #agj4 ,a4 ,prime conductor4 ,b4 ,upper brass-plate4 ,c4 ,lower ditto4 ,the figures are seen between ,b and ,c4 ,twenty-sixth ,experiment4 ,suspend from the prime conductor by a chain a circular brass plate and under this place another supported by a brass adjusting stand4 ,if pith figures of men and women are placed on the lower plate1 they rise directly the machine is turned1 although sometimes1 in consequence of irregularity in the adjustment of the centre of gravity1 they perversely dance on their heads instead of the usual position2 out of half a dozen figures1 one only perhaps will be found to dance well1 by alternately jumping to the upper plate and falling to the lower one to discharge the excess of electricity2 and indeed the experiment will be found to succeed better with one or two only on the plate instead of a number1 as they cling together and impede each other's movements4 7,fig4 #agj47 ,page #ahf ,twenty-seventh ,experiment4 ,an assistant provided with a wig of well-combed hair presents a most ridiculous appearance when standing on the insulating stool and connected by a wire with the prime conductor of the electrical machine1 every hair1 when not matted together1 standing out in the most absurd manner1 when the machine is put in motion4 ,twenty-eighth ,experiment4 ,whilst standing on the stool1 sparks may be obtained from his body1 and if some tow is tied over a brass ball1 and moistened with a little ether1 and presented to the tip of his finger1 a spark flies off which quickly sets fire to the inflammable liquid4 ,illustration3 ,fig4 #aga4 ,a ,a ,a4 ,a ring of brass wire supported on a glass pillar inside which the spiral tube1 ,b1 revolves1 and produces beautiful and ever-changing circles of light1 when connected with the conductor1 ,c1 of the electrical machine4 ,twenty-ninth ,experiment4 ,if small discs of tinfoil1 cut out with a proper stamp1 are pasted in continuous lines over plate glass1 or spirally round glass tubes1 a very ,page #ahg pretty effect is produced when they receive the sparks from the electrical machine1 and the passage of the electricity from one disc to the other produces a vivid spiral or other line of light4 ,when the tube is mounted in a proper apparatus1 so as to revolve whilst the sparks pass down the spiral tube1 the effect of the continuous electric sparks is much heightened4 7,fig4 #aga47 ,thirtieth ,experiment4 ,a great variety of experiments1 depending on the proper arrangement of discs of tinfoil on various tubes of coloured glass are manufactured1 and some in the form of windmills1 the sails being made luminous by the passage of the electricity4 ,the names of illustrious electricians1 beautiful crescents1 stars1 and even profile portraits1 have been produced in continuous streams of electric sparks4 ,thirty-first ,experiment4 ,when an electrified body is brought towards another which is not electrical1 the latter is thrown into the opposite state of electricity as long as the excited body remains in its neighbourhood2 and this condition of electrical disturbance1 set up without any contact or supply of electricity1 is called induction1 and involves a vast number of interesting facts1 which are thoroughly discussed in ,dr4 ,noad's excellent work on electricity1 but can only be briefly alluded to here4 ,illustration3 ,fig4 #agb4 ,the lengths of brass wire supported on glass rod pillars indented by blowpipe1 so as to retain the brass wires with the pith balls hanging from each series1 the letters ,p and ,n mean ,positive and ,negative1 and the signs for these terms are placed above4 ,the letters ,p and ,n are painted on the blocks which support the glass rods4 ,if a number of lengths of brass wire1 supplied with balls at the extremities1 are supported on glass legs and arranged in a line1 with a little pith ball attached to a thread hanging from each end of the length of brass wire1 the effect of induction is shown very nicely2 and when an excited glass rod is brought towards one end of the series1 the rising of the pith balls to each other betrays the change which has occurred in the electrical state of the brass wires by the mere neighbourhood of the excited glass tube4 ,the glass tube is electrified positively1 and attracts the negative electricity from the brass wire towards the end nearest to it2 ,page #ahh the other extremity of the brass wire is found to be in the positive state1 and this re-acting on the next1 and so on throughout the lengths1 completes the electrical disturbance in the whole series4 7,fig4 #agb47 ,thirty-second ,experiment4 ,illustration3 ,fig4 #agc4 ,a ,a4 ,large circular tin or brass disc with turned-up edge half an inch deep1 and containing the resinous mixture ,b1 which is rubbed with the warm flannel4 ,c ,c4 ,the upper plate supported by the glass handle ,d1 a pith ball attached to a wire shows the electrical excitation1 and the spark is supposed to be passing to the hand ,e4 ,if an insulated brass rod 7such as has been described in the last experiment7 is touched by the finger whilst under induction1 it remains permanently electrified on the removal of the disturbing electrified body2 and it is on this principle that the useful electrical machine called the ,electrophorus is constructed4 ,this constant electrical machine--for it will remain in action during weeks and months if kept sufficiently dry--was invented by ,volta in the year #aggd1 and has been brought to great perfection by ,mr4 ,lewis ,m4 ,stuart1 of the ,city of ,london ,school2 so that with a little additional apparatus the whole of the fundamental principles of electricity can be demonstrated4 ,it consists of a flat brass or tin circular dish about two feet in diameter and half an inch deep1 which is filled with a composition of equal parts of black rosin1 shell-lac1 and ,venice turpentine2 the rosin and the ,venice turpentine being first melted together1 and the shell-lac added afterwards1 care of course being taken that the materials do not boil over and catch fire1 in which case the pot must be removed from the heat1 and a piece of wet baize or other woollen material thrown over it4 ,another tin or brass circular plate of twelve inches diameter1 and supported in the centre with a varnished glass handle nine inches long1 is also provided1 and the resinous plate being first excited by several smart blows with a warm roll of flannel1 the plate held by the glass handle is now laid upon the centre of the resinous one1 and if removed directly afterwards1 does not afford the electric spark2 but if1 whilst standing upon the excited resinous plate1 it is touched1 and then removed by the glass handle1 a powerful electric spark is obtained2 and this may be repeated over and over again with the like results1 provided the plate with the glass handle is touched with the finger just before lifting it from the resinous plate4 7,fig4 #agc47 ,page #ahi ,the electricity excited on the resinous plate is not lost1 and by induction sets up the opposite condition in the plate with the glass handle4 ,the resinous plate1 being excited with negative electricity1 disturbs the electrical quiescence of the upper plate1 and positive electricity is found on the surface touching the resinous plate1 and negative electricity on the upper one1 so that when it is removed without being touched1 the two electricities come together again1 and no spark is obtained2 but if1 as already described1 the upper plate is touched whilst under induction1 then positive electricity appears to pass from the finger to the negative electricity on the upper side of the plate1 when the two temporarily neutralize each other1 and then1 when the plate is removed1 the excess of electricity derived from the earth through the finger becomes apparent4 ,induction requires no sensible thickness in the conductors1 and can be just as well produced on a leaf of gold as on the thickest plate of metal2 and it should be remembered that non-conductors do not retain their state of electrical excitation when the disturbing cause is removed1 whereas conductors possess this power1 and this fact brings us to the consideration of the ,leyden jar4 ,thirty-third ,experiment4 ,if one side of a dry glass plate is held before and touches a brass ball proceeding from the prime conductor of an electrical machine whilst in action1 the other side is soon found to be electrical2 this does not arise from the conduction of the electricity through the particles of the glass1 but is produced by induction1 the side nearest the ball being in the positive state1 and the other side negative3 as glass is a non-conductor of electricity1 the effect is much increased by coating each side with tinfoil1 leaving a margin of about two inches of uncovered glass round the covered portion1 then1 if one side of such a plate is held to the prime conductor of the electrical machine1 and the other connected with the ground1 a powerful charge is accumulated2 and if the opposite sides are brought in contact with a bent brass wire1 a loud snapping noise is heard1 and the two electricities resident on either side of the glass come together with the production of a brilliant spark1 or if the hands are substituted for the bent brass wire1 that most disagreeable result is obtained--viz41 an electric shock2 hence these glass plates are sometimes fitted up as pictures1 and when charged and handed to the unsuspecting recipient1 he or she receives the electric discharge to the great discomfort of their nervous system4 ,mica is sometimes substituted for glass1 and the late ,mr4 ,crosse1 the celebrated electrician1 constructed a powerful combination of coated plates of this mineral4 ,it consisted of seventeen plates of thin mica1 each five inches by four1 coated on both sides with tinfoil within half an inch of the edge4 ,they were arranged in a box with a glass plate between each mica plate1 all the upper sides were connected by strips of tinfoil to one side of the box1 and all the under surfaces in the same manner with the opposite extremity of the box4 ,they were charged like an ordinary ,leyden battery4 ,page #aij ,thirty-fourth ,experiment4 ,if the glass plate coated with tinfoil is charged1 and then placed upright on a stand1 it may be slowly discharged by placing a bent wire on the edge with the extremities covered with pith balls4 ,the wire balances itself1 and continues to oscillate with noise until the electricities of the two surfaces neutralize each other4 7,fig4 #agd47 ,illustration3 ,fig4 #agd4 ,a ,a4 ,glass plate or stand coated with tinfoil on each side1 ,b4 ,c4 ,wire with pith balls oscillating during the discharge of the glass plate4 ,thirty-fifth ,experiment4 ,it is easy to imagine the glass plate of the last experiment rolled up into the more convenient form of the ,leyden jar1 which consists of a glass vessel lined both inside and out with tinfoil1 leaving some two or three inches of the glass round the mouth uncovered and varnished with shell-lac2 a piece of dry wood is fitted into the mouth of the jar1 through which a brass wire and chain are passed1 and the end outside is fitted with a ball4 ,the ,leyden jar is charged by holding the ball to the prime conductor of the electrical machine until a sort of whizzing noise is heard1 caused by the excess of electricity passing round the uncovered part of the jar and not through it1 as the smallest crack in the glass of the ,leyden jar would render it useless4 ,electricity is sometimes called a fluid1 and the fact of collecting it like water in a jar1 helps us to understand this analogy4 ,the noise1 the bright spark1 or the shock are obtained by grasping the outside with one hand and touching the ball with a brass wire held in the other4 7,fig4 #age47 ,illustration3 ,fig4 #age4 ,the ,leyden jar and brass wire discharger4 ,thirty-sixth ,experiment4 ,the jar is silently discharged if the balls are removed from the discharger and points used instead2 so1 also1 the whole of the electricity produced by an electrical machine in full action may be readily drawn off by a pointed conductor1 such as a needle1 placed at the end of a brass wire4 ,electricity passes much more rapidly through points than rounded surfaces1 hence the reason why all parts of electrical apparatus are free from sharp points and rough asperities4 ,page #aia ,thirty-seventh ,experiment4 ,extremely thin wires may be burnt by passing the charge of a large ,leyden jar through them4 ,the show jars1 called specie jars1 usually decorated and placed in the windows of chemists' shops1 make excellent ,leyden jars1 when not too thick2 and with two of the largest1 all the interesting effects produced by accumulated electricity may be displayed4 ,to pass the discharge through wires1 nothing more is required than to strain them across a dry mahogany board1 between two brass wires and balls1 and if a sheet of white paper is placed under them1 most curious markings are produced by the fine particles of the deflagrated metal blown into the surface of the paper4 ,an arrangement of two or more ,leyden jars is usually called a ,leyden ,battery1 just as a single cannon is spoken of as a gun1 whilst two or more constitute a battery4 7,fig4 #agf47 ,illustration3 ,fig4 #agf4 ,a4 ,mahogany board with a sheet of white paper and three pairs of brass wires and balls fixed in the wire1 three on each side4 ,the thin wires are stretched between the balls1 and the lower one is in course of deflagration4 ,b ,b4 ,charged large ,leyden battery of two jars2 the arrows indicate the path of the electricity4 ,thirty-eighth ,experiment4 ,little models of houses1 masts of ships1 trees1 and towers are sold by the instrument makers1 and by placing a long balanced wire on the top of the pointed wire of a large ,leyden jar1 having one end furnished with wool to represent a cloud1 a most excellent imitation of the effects of a charged thunder-cloud is produced4 ,the mechanical effect of a flash of lightning has been analysed1 and it has been stated1 in one instance1 that the power developed through fifty feet was equal to a #ab1bbj horse-power engine1 or about the power of the engines of the ,great ,eastern1 and that the explosive power was equal to a pressure of three hundred millions of tons4 7,fig4 #agg47 ,page #aib ,illustration3 ,fig4 #agg4 ,a4 ,charged ,leyden jar with balanced wire and wool at ,b1 representing a thunder-cloud4 ,c4 ,the obelisk overturned with the discharge4 ,d4 ,another model of the gable end of a house2 the square pieces of wood fly out when the continuity of the conductor is broken4 ,it was the learned but humble minded ,dr4 ,franklin who established the identity between the mimic effects of the electrical machines 7such as have been described71 and the awe-inspiring thunder and lightning of nature4 ,a copper rod1 half an inch thick1 pointed and gilt at the extremity1 and carried to the highest point of a building1 will protect a circle with a radius of twice its length4 ,the bottom of the rod must be passed into the earth till it touches a damp stratum4 ,illustration3 ,fig4 #agh4 ,a storm4 ,page #aic ,,chapter ,,xiv4 ,,voltaic ,,electricity4 ,in describing the various means by which electricity may be obtained1 it was stated that ,chemical ,action was a most important source of this remarkable agent2 at the same time it must be understood that it is not every kind of chemical action which is adapted for the purpose2 there are certain principles to be rigidly adhered to--first1 in the generation of the force2 and secondly1 in carrying it by wires so as to be applicable either for telegraphic purposes1 or for the highly valuable processes of electrotyping and electro-silvering1 plating1 and gilding4 ,a lighted candle1 or an intense combustion of coal1 coke1 or charcoal1 no doubt involves the production of electricity1 but there are no means at present known by which it may be collected and conducted2 when that problem is solved1 the cheapest voltaic battery will have been constructed1 in which the element decomposed is charcoal1 and not a metal1 such as iron or zinc4 ,the first and most simple experiment that can be adduced in proof of electrical excitation by chemical means1 is to take a bit of clean zinc and a clean half-crown1 and placing one on the tongue and the other below it1 as long as they remain separate no effect is observed1 but directly they are made to touch each other1 whilst in that position1 a peculiar thrill is rendered evident by the nerves of the tongue1 which in this case answers the same purpose as the electroscope already described1 and in a short time a peculiar metallic taste is perceptible4 ,it has been stated over and over again that it was to a somewhat similar circumstance we owe the discovery of voltaic electricity1 and the story of the skinned frogs agitated and convulsed by an accidental communication with two different metals1 or1 as some say1 with the electricity from an ordinary machine1 has been repeated in nearly every work on the science4 ,professor ,silliman1 however1 asserts that the galvanic story is doubtful1 and is a fabrication of ,alibert1 an ,italian writer of no repute1 and that greater merit is due to ,galvani than that of being merely the accidental discoverer of this kind of electricity1 because he had been engaged for eleven years in electro-physiological experiments1 using frogs' legs as electroscopes4 ,it was whilst experimenting on animal irritability1 ,galvani noticed the important fact that when the nerve of a dead frog1 recently killed1 was touched with a steel needle1 and the muscle with a silver one1 no convulsions of the limb were produced until the two different metals were brought in contact1 and he explained the cause of these singular after-death contortions by supposing that the nerves and muscles of all animals were in opposite states of electricity1 and that these nervous contractions were caused by the annihilation1 for the time1 of this condition1 by the interposition of a good conductor between them4 ,this theory of ,galvani had several opponents1 one of whom1 the ,page #aid celebrated ,volta1 succeeded in pointing out its fallacy2 he maintained that the electrical excitement was due entirely to the metals1 and that the muscular contractions were caused by the electricity thus developed passing along the nerves and muscles of the dead animal4 ,to ,volta we are indebted for the first voltaic battery1 and the distinguished philosopher may truly be said to have laid the foundation of this now commercially valuable branch of science4 ,first ,experiment4 ,if a plate of clean bright zinc is placed in a vessel containing some dilute sulphuric acid1 energetic action occurs from the oxidation of the metal1 and its union as an oxide with the acid1 and the escape of a multitude of bubbles of hydrogen gas4 ,after the action has proceeded some time1 the zinc may be removed1 and if a little quicksilver is now rubbed over the surface with a woollen rag tied on the end of a stick1 it unites with the metal1 and the surface of the zinc assumes a brilliant silvery appearance1 and is said to be amalgamated4 ,in that condition it is no longer acted upon by dilute sulphuric acid1 and for the sake of economy this is the only form in which zinc should be employed in the construction of voltaic batteries or single circles4 ,if a clean plate of copper1 with a wire attached1 is now placed in the dilute acid opposite to and not touching the amalgamated zinc plate1 which may also be furnished with a conducting wire1 no bubbles of hydrogen escape until the wires from the two metals are brought in contact1 and then1 singular to relate1 the hydrogen escapes from the copper plate1 whilst the oxygen is rapidly absorbed by the zinc1 and a current of electricity will now be found to pass from the zinc through the fluid to the copper1 and back again through the wire to the starting point1 and if the wires are disconnected1 the chemical action ceases1 and no more electricity is produced4 7,fig4 #agi47 ,illustration3 ,fig4 #agi4 ,a single voltaic circle1 consisting of a zinc and copper plate 7marked ,z and ,c7 in dilute acid4 ,the arrows show the direction of the current4 ,the passage of the current of electricity is not discoverable by the electroscope1 because it is adapted only to indicate electricity of high tension or intensity1 such as that produced from the electrical machine1 which will pass rapidly through a certain thickness of air1 and cause pith balls to stand out and repel each other2 such effects are not producible by a single voltaic circle1 or even an ordinary voltaic battery1 although one comprising some hundreds of alternations would produce ,page #aie an effect on a delicate electrometer2 hence voltaic electricity is said to be of low intensity1 and this property makes it much more useful to mankind1 because it has no desire to leave a metallic path prepared for it1 and does not seize the first opportunity1 like the electricity from the electrical machine1 to run away to the earth through the best and shortest conductor offered for it4 ,if electricity had only been producible by friction1 we should never have heard of electrotyping1 and the other useful applications of electrical force of low intensity4 ,second ,experiment4 ,to ascertain the passage of a current of voltaic electricity1 the instrument called the galvanometer needle is provided1 which consists of a coil of copper wire surrounding a magnetic needle1 so as to leave the latter freedom of motion from right to left1 or vice vers4 ,when this coil is made part of the voltaic circle it becomes magnetic1 and reacting on the magnetized needle1 deflects it to one side or the other1 according to the direction of the current4 7,fig4 #ahj47 ,illustration3 ,fig4 #ahj4 ,a galvanometer needle1 consisting of a coil of covered copper wire1 the ends of which terminate at the binding screws4 ,the magnetic needle is suspended on a point in the centre1 and the coil is surrounded with a graduated circle4 ,third ,experiment4 ,if a number of simple voltaic circles1 such as the one described in the first experiment1 are connected together1 they form a voltaic battery1 in which of course the quantity of electricity is greatly increased4 ,batteries of all kinds1 from the original ,volta's pile1 consisting of round zinc and copper plates soldered together with interposed cloth moistened with dilute sulphuric acid1 or his couronne des tasses1 consisting of zinc and silver wires soldered together in pairs1 and placed in glass cups containing dilute acid1 to the improved batteries of ,cruikshank1 ,wilkinson1 ,babington1 ,wollaston1 and the still more perfect arrangements of ,daniell1 ,mullins1 ,shillibeer1 and ,grove1 have been from time to time recommended for their own peculiar features4 ,amongst these several inventions1 none will be found more useful than the constant battery of ,daniell for electrotyping1 silvering1 gilding1 and other purposes1 and ,grove's battery for all the more brilliant results1 such as the deflagration of the metals or the production of the electric light4 ,the construction of the ,daniell and ,grove batteries will therefore be described4 ,the former consists of a cylindrical vessel made of copper1 in which is suspended or placed 7as it is open at the top7 a membranous1 brown-paper1 canvas1 or porous earthenware tube1 containing an amalgamated rod of zinc4 ,to charge this arrangement1 a strong solution of sulphate of copper1 with some sulphuric acid1 is poured into the copper vessel1 which is provided usually with a sort of ,page #aif colander at the top to hold crystals of sulphate of copper1 and in the porous tube containing the zinc rod is poured dilute sulphuric acid4 ,a number of these cylinders of copper1 twenty inches high and three inches and a half in diameter1 arranged in wooden frames to the number of twenty1 afford a quantity of electricity sufficient to demonstrate all the usual phenomena4 7,fig4 #aha47 ,illustration3 ,fig4 #aha4 ,a ,a4 ,copper cylindrical vessel with colander to hold the crystals of sulphate of copper4 ,b4 ,the amalgamated zinc rod inside the porous cell ,c ,c4 ,d4 ,a series of single cells forming a ,daniell's battery4 ,professor ,grove's battery consists of a flat glazed earthenware vessel containing a flat porous cell4 ,an amalgamated zinc plate is placed outside the porous cell1 and a platinum plate inside the latter4 ,the arrangement is put in action by pouring dilute sulphuric acid round the zinc and strong nitric acid inside the porous cell4 ,a set of ,grove's nitric acid battery1 as manufactured by ,messrs4 ,elliott1 ,brothers1 of #cj1 ,strand1 with fifty pairs of sheet platinum1 five inches by two inches and a quarter1 and double amalgamated zinc plates1 flat porous cells1 and separate earthenware troughs for each pair1 and stout mahogany stand1 arranged in ten series of five pairs1 will evolve with a proper voltameter one hundred cubic inches of the mixed gases per minute from the decomposition of water1 and will exhibit a most brilliant electric light1 when arranged as a single series of fifty pairs of plates4 ,even thirty pairs exhibit the most splendid effects1 whilst forty may be regarded as the happy medium1 giving all the results that can be desired4 7,fig4 #ahb47 ,the advantage of employing amalgamated zinc is very prominently illustrated whilst using any powerful arrangements of either ,daniell's or ,grove's batteries1 as they will remain for hours quiescent1 like a giant asleep1 until the terminal wires of the series are brought in contact ,page #aig either through the intervention of some fluid under decomposition or by means of charcoal points4 ,the author had the pleasure of witnessing at ,king's ,college some of the effects of an enormous battery1 prepared by the late ,professor ,daniell1 and consisting of seventy of his cells4 ,illustration3 ,fig4 #ahb4 ,a ,a4 ,amalgamated zinc plate in flat earthenware trough4 ,attached to a binding screw is the platinum plate in porous cell1 ,c ,c4 ,d4 ,a series of single cells forming a ,grove's battery4 ,a continuous arch of flame was produced between two charcoal points1 when distant from each other three quarters of an inch1 and the light and heat were so intense that the professor's face became scorched and inflamed1 as if it had been exposed to a summer heat4 ,the rays collected by a lens quickly fired paper held in the focus4,c ,footnote ,c3 ,by the light from the same battery photogenic drawings were taken1 and the heating power was so great as to fuse with the utmost readiness a bar of platinum one-eighth of an inch square2 and all the more infusible metals1 such as rhodium1 iridium1 titanium1 c41 were melted like wax when placed in small cavities in hard graphite and exposed to the current of electricity4 ,fourth ,experiment4 ,it is by chemical action the electricity is produced1 and as action and reaction are always equal1 but contrary1 we are not surprised to find that the electricity from the voltaic battery will in its turn decompose chemically many compound bodies1 of which water is one of the most interesting examples4 ,it was in the year #ahjj1 and immediately after ,volta's announcement to ,sir ,joseph ,banks of his discovery of the pile1 that ,messrs4 ,nicholson and ,carlisle constructed the first pile in ,england1 consisting of thirty-six half-crowns1 with as many discs of zinc and pasteboard soaked in salt water4 ,these gentlemen1 whilst experimenting with the pile1 observed that bubbles of gas escaped from the platinum wires immersed in water and connected with the extremities of the ,volta's pile1 and covering the wires with a glass tube full of water1 on the #bnd of ,may1 #ahjj1 they completed the splendid discovery of the fact that the ,volta's current had the power to decompose water and other chemical compounds4 ,page #aih ,in #ahja1 ,davy had succeeded to a vacant post in the ,royal ,institution1 and on ,oct4 #fth1 #ahjg1 made his transcendent discovery of potassium with the aid of the voltaic battery1 and from that and other experiments inferred that the whole crust of the globe was composed of the oxides of metals4 ,to exhibit the decomposition of water1 two platinum plates with proper connecting wires1 passing to small metallic cups full of mercury1 are cemented inside a glass vessel1 which is then filled with dilute sulphuric acid4 ,just above the platinum plates and over them1 stand two glass tubes also containing the same fluid in contact with the battery4 ,two measures of hydrogen are found in one tube1 and one of oxygen in the other4 7,fig4 #ahc47 ,illustration3 ,fig4 #ahc4 ,a ,a4 ,a finger glass with two holes drilled to pass the wires through1 which are imbedded in cement up to the platinum plates4 ,b ,b4 ,glass tubes1 closed at one end and open at the other1 which are placed over the platinum plates to receive the liberated oxygen and hydrogen4 ,the scale at the side shows the respective volumes of two of ,h to one of ,o4 ,to measure the quantity power of the voltaic battery1 an important instrument invented by ,faraday is used4 ,it consists of separate platinum plates cemented in a wooden stand1 and over which a capped air-jar with a bent pipe is also cemented4 ,this apparatus contains dilute sulphuric acid of the same strength as that used in the battery under examination1 and by taking the time1 the quantity of the mixed oxygen and hydrogen gases producible by a battery per minute is accurately determined1 the gases of course being collected in a graduated jar4 7,fig4 #ahd47 ,illustration3 ,fig4 #ahd4 ,a4 ,gas jar with cap and bent tube passing to the graduated tube ,c2 the jar is cemented in the same stand which carries the connecting cups1 wires1 and platinum plates1 which are bent round each other to improve the action of the voltameter4 ,page #aii ,fifth ,experiment4 ,by grouping the simple circles forming a voltaic battery in various numerical relations1 the quantity and intensity effects are modified4 ,thus1 if a series of thirty pairs of ,grove's battery are all connected together in consecutive order1 the smallest quantity and the largest intensity effect is produced4 ,if changed to two groups of fifteen each1 the quantity is doubled--that is to say1 it will produce double the quantity of the mixed gases from the voltameter with half the intensity4 ,if arranged in three groups of ten each1 it is trebled with a proportional loss of intensity1 until the grouping reaches six series of five each1 when a maximum supply of the mixed gases is obtained from the voltameter4 ,in arranging the groups1 all the zinc ends of each series are connected1 and all the platinum ends are likewise joined by proper wires4 ,sixth ,experiment4 ,a plate-glass trough1 containing a few grains of iodide of potassium dissolved in water with some starch1 is quickly decomposed into its elements by placing in two platinum plates and connecting them with the wires of the voltaic battery4 ,if the glass trough is divided in the centre with a bit of cardboard1 the purple colour of the iodine and starch is shown very beautifully on one side1 but not on the other1 as iodine is liberated at one pole and the alkali at the other4 7,fig4 #ahe47 ,illustration3 ,fig4 #ahe4 ,a ,a4 ,a glass trough containing the salt dissolved in water1 and divided temporarily with a bit of cardboard1 ,b4 ,c ,c are the two platinum plates connected with the battery1 and the shaded side is supposed to represent the liberation of the iodine4 ,seventh ,experiment4 ,some solution of common salt coloured with sulphate of indigo and placed in the trough is decomposed into chlorine1 which bleaches one side of the indigo solution1 and the alkali liberated on the other does not affect it4 ,eighth ,experiment4 ,some nitrate of potash dissolved in water and coloured with litmus placed in the glass trough1 changes red on one side of the cardboard by the liberation of acid1 and is not affected on the other4 ,in these experiments the oxygen1 iodine1 chlorine1 and nitric acid are liberated at the electro-positive pole1 and are hence termed electro-negative bodies1 whilst hydrogen and the alkalies are set free at the electro-negative pole1 and are therefore called electro-positive bodies4 ,page #bjj ,faraday has modified these terms1 and calls the two classes anions and cathions1 and the two poles anodes and cathodes4 ,anode1 from ,greek3 ana1 up1 and ,greek3 hodos1 a way3 the way which the sun rises4 ,anions1 from ,greek3 ana1 up1 and ,greek3 eimi1 to go3 that which goes up2 a substance which passes to the anode during the passage of a current of electricity4 ,cathode1 from ,greek3 kata1 down1 and ,greek3 hodos1 a way3 the way which the sun sets4 ,cathion1 from ,greek3 kata1 down1 and ,greek3 eimi1 to go3 that which goes down2 a substance which passes to the cathode during the passage of electricity from the anode to the cathode4 ,ninth ,experiment4 ,in the process of the electrotype is presented a valuable application of the chemical power of the voltaic circle or battery1 and it may be conducted either as a single cell operation or by distinct batteries4 ,in the former case the most simple arrangement will suffice2 the only articles necessary are--a large mug or tumbler2 some brown paper and a ruler2 a bit of amalgamated zinc1 four inches long and half an inch wide2 a short length of copper wire2 some black lead1 blue vitriol1 and oil of vitriol4 ,the mould from which the electrotype is to be taken can be made of common sealing wax1 plaster of ,paris1 white wax1 gutta percha1 or fusible alloy4 ,supposing the first to be selected--viz41 a common seal1 it is first thoroughly black-leaded1,d then one end of the copper wire is bent round the top of the amalgamated zinc1 and the other is gently warmed and melted into the side of the seal1 leaving a small portion uncovered by the wax1 which is then well black-leaded4 ,a few ounces of blue vitriol are dissolved in boiling water1 and when cold the solution is poured into the tumbler1 and the porous cell to contain the mixture of eight parts water to one of sulphuric acid is made by rolling the brown paper three or four times round the ruler and closing the end1 and fixing the side with a little sealing wax4 ,the porous cell of brown paper is now filled with the dilute acid1 and placed in the tumbler containing the solution of blue vitriol1 the amalgamated zinc being arranged in the paper cell1 and the attached seal in the copper solution2 in about twelve hours a good deposit of copper is produced1 and a perfect cast in metal of the seal obtained4 7,fig4 #ahf47 ,footnote ,d3 ,the application of plumbago1 or black lead1 for electrotype purposes1 was first made by the late lamented ,mr4 ,robert ,murray4 ,illustration3 ,fig4 #ahf4 ,a ,a4 ,the tumbler containing the solution of sulphate of copper4 ,b ,b4 ,the brown paper cell containing the dilute sulphuric acid1 inside which is the amalgamated zinc with wire attached to the seal ,d4 ,page #bja ,messrs4 ,elliott provide every kind of convenient vessel for the purpose1 and in the picture below it will be noticed that the single cell apparatus1 though not so economical as the simple tumbler arrangement already described1 is perhaps more convenient for electrotyping4 7,fig4 #ahg47 ,illustration3 ,fig4 #ahg4 ,a4 ,single cell apparatus with proper vessel1 porous tube1 and binding screws4 ,b4 ,a large trough divided by a diaphragm of biscuit-ware or very thin porous wood4 ,tenth ,experiment4 ,illustration3 ,fig4 #ahh4 ,a4 ,a single cell1 ,daniell's1 attached to ,b1 the trough containing the mould and the plate of copper4 ,below is a ,smee's battery ready to be attached to a larger trough for the purpose of electrotyping a great number of moulds at the same time4 ,a single cell apparatus is only adapted to produce small electrotypes1 but when larger ones are required1 a separate battery of three or four ,page #bjb ,daniell's or ,smee's cells is required2 and it is usual to place the mould to be copied in a separate wooden trough1 attaching it to the cathode wire1 whilst a copper plate is connected with the anode1 so that as the solution of sulphate of copper undergoes decomposition by the passage of the electricity1 it is kept almost in a normal state1 in consequence of the oxygen of the water and the acid passing to the copper plate1 which they attack and dissolve as fast as the oxide of copper and hydrogen are liberated at the cathode1 where the latter deoxidizes the oxide of copper1 and by a secondary action deposits metallic copper2 the object being to dissolve fresh metal as the copper is deposited on the mould4 7,fig4 #ahh47 ,eleventh ,experiment4 ,to silver electrotypes or other brass and copper articles1 the first attention must be paid to the cleanness of them2 and when an electrotype is just removed from the copper solution1 and washed in clean water1 it is at once ready to receive the coating of silver2 otherwise1 if it has been handled1 or is slightly greasy1 it should be first boiled in a solution of common washing soda1 and then the oxide removed by passing it rapidly in and out of some ,dipping ,acid1 which is prepared by mixing together equal parts of oil of vitriol and nitric acid2 when removed from the ,dipping ,acid1 it must be well washed in water1 and may remain under the surface of the water until the silvering solution is ready4 ,a silver solution may be prepared by dissolving a sixpence in some nitric acid contained in a flask2 it is then poured into a solution of common salt1 which precipitates the chloride of silver1 and leaves the copper in solution--the latter is poured off when the chloride has subsided1 and after being well washed in some boiling water1 is dissolved in a solution of cyanide of potassium4 ,if a clean electrotype is plunged into this solution1 it is immediately covered with a very thin coating of silver1 which of course would soon wear off1 and in order to increase the thickness of the silver deposit1 a single cell arrangement may be constructed of a large gallipot containing a wide porous cell and a circle of amalgamated zinc around it2 the arrangement is set in action by pouring a solution of salt 7or1 still better1 sal ammoniac7 into and around the porous vessel1 and the silvering solution into the latter2 a connecting wire passes from the zinc1 and the article being attached to it1 is now plunged into the porous cell1 when a current of electricity slowly passes and deposits the silver on the copper article4 7,fig4 #ahi47 ,illustration3 ,fig4 #ahi4 ,the gallipot containing the solution of sal ammoniac1 with the circular amalgamated zinc with wire and binding screw to which the medal is attached1 and contained in the porous vessel holding the silvering solution and medal4 ,page #bjc ,twelfth ,experiment4 ,separate batteries and large troughs containing a solution of cyanide of silver in cyanide of potassium are used on a grand scale in the electro-plating establishment of ,messrs4 ,elkington of ,birmingham1 where the finest specimens of the art are to be obtained2 a plate of silver being attached to the anode to supply the loss of silver in these troughs4 ,thirteenth ,experiment4 ,the art of gilding by the agency of electricity is quite as simple as the processes already described1 although greater care is necessary to avoid any loss of the precious metal4 ,a small bit of gold is dissolved in a mixture of three parts muriatic acid and one of nitric acid1 which forms the chloride of gold4 ,this is then digested with an excess of calcined magnesia1 and the gold is precipitated as an oxide of the metal2 the latter is collected and washed1 and then boiled in strong nitric acid to remove the magnesia clinging to it1 and being again thoroughly washed with water1 is dissolved in a solution of cyanide of potassium1 forming a solution of cyanide of gold and potassium1 which may be placed in the porous cell of the single cell arrangement already described in the ,eleventh ,experiment4 ,fourteenth ,experiment4 ,the safest and surest mode of making a gilding solution is to dissolve some cyanide of potassium in water in a gallipot1 and having placed a porous vessel therein containing the same solution1 put a plate of copper into the porous cell1 and some thin foil of pure gold into the gallipot2 connect the gold with the anode of a single cell of ,daniell1 and the copper in the porous cell with the cathode1 and in a few hours sufficient gold will be dissolved for the purpose of gilding4 ,it is usually recommended to warm the gilding solution till it reaches a temperature of about #aej ,fahr41 and a very moderate battery power is employed in ,electro ,gilding4 ,indeed the same arrangement1 shown in the ,eleventh ,experiment1 ,fig4 #ahi1 will also answer for the gilding solution4 ,after being gilt1 the articles may be rubbed with a little tripoli1 or burnished 7with taste7 by the handle of a key4 ,fifteenth ,experiment4 ,passing on to the more brilliant results obtainable from a powerful voltaic battery 7of at least thirty pairs of ,grove71 the beautiful incandescence of platinum wire may first be noticed4 ,if a wire of this metal is stretched between the brass standards of two ring stands1 the length must be proportioned to the power of the battery2 the adjustment can be made very conveniently by twisting the platinum wire on one ring stand1 and then leaving the other end loose1 the second ring stand may be brought nearer and nearer to the first1 until the desired intensity of ,page #bjd light from the incandescent wire is obtained4 7,fig4 #aij47 ,if the wire is contained in a glass tube the cooling effect of currents of air is prevented1 and a much greater length of wire can be made hot4 ,illustration3 ,fig4 #aij4 ,a ,a4 ,two ring stands with the battery wires ,b ,b 7which should be a convenient length7 attached4 ,c4 ,platinum wire1 fixed end4 ,d4 ,the other end held in one hand and shortened as the stand is moved by the other hand4 ,sixteenth ,experiment4 ,with the same arrangement1 a chain composed of alternate links of silver and platinum wire presents a very pretty effect1 every alternate link of platinum being incandescent1 whilst the silver1 from its excellent conducting power1 remains comparatively cool4 ,seventeenth ,experiment4 ,fireworks or gunpowder1 arranged in proper cases1 are fired at a great distance from the voltaic battery by heating a thin iron or platinum wire contained within them by the passage of the electricity2 and submarine and other explosions of gunpowder by the same agency have become a common engineering operation4 7,fig4 #aia47 ,illustration3 ,fig4 #aia4 ,a4 ,a ,gerb firework with two holes punctured1 through which the bit of iron wire passes1 and is wound round the battery wires tied to the outside of the case4 ,c4 ,a gut bladder containing the thin wire and powder for a miniature submarine explosion4 ,during the operation of blasting the hard marl rocks in the ,river ,severn by ,mr4 ,edwards1 ,c4,e41 a number of holes were made side by side in the bed of the river1 and cartridges formed of strong duck or canvas1 tapered at the bottom1 were filled with charges of powder from two to four pounds1 according to the depth of the marl2 thus1 two pounds for four feet1 three pounds for four feet six inches1 and four pounds for five feet4 ,into the bag were conveyed the wires of the voltaic battery1 or ,bickford's fuse1 and being then coated with pitch and tallow1 and finally greased all over and dusted with whitening1 they rarely failed1 and were all fired simultaneously under water4 ,the pitch and tallow first1 and afterwards the simple tallow1 effectually excluded the water from the gunpowder contained in the canvas bag4 ,page #bje ,eighteenth ,experiment4 ,the burning of various metals by the battery is displayed with great effect by ,de la ,rue's discharger1 as also the incandescence of the charcoal points producing the electric light4 ,the illuminating power derived from a forty-cell ,grove's battery of the ordinary size is about equal to the light of #ejj candles4 ,illustration3 ,fig4 #aib4 ,de la ,rue discharger1 containing a series of six pairs of different substances1 such as charcoal1 iron1 lead1 zinc1 copper1 antimony1 in six pair of crayon holders1 and turning on a centre1 so as to be changed at pleasure4 ,fizeau and ,foucault have made a careful comparison of the light obtained from #ib carbon couples as arranged in a ,bunsen's battery1 and of the oxy-hydrogen1 or ,drummond ,light1 as compared with that of the sun1 and they state that ,on a clear ,august day1 with the sun two hours high1 the electric light 7assuming the sun as unity7 bore to it the ratio of one to two and a half--i4e41 the sun was two and a half times more powerful1 while the ,drummond ,light was only #a_/adfth that of the sun4 ,bunsen found the light from #dh carbons equal to #egb candles4 ,in ,bunsen's battery carbon is substituted for the platinum in ,grove's arrangement2 and simultaneously with ,bunsen1 ,cooper 7in ,england7 had applied charcoal for the same purpose4 ,at night the giant ship 7,polyphemus like7 is to have an electric light at the mast-head whilst steaming across the ,atlantic4 ,illustration3 ,fig4 #aic4 ,great ,eastern1 with electric light4 ,page #bjf ,,chapter ,,xv4 ,,magnetism ,,and ,,electro-,,magnetism4 ,if a small helix1 or coil of covered wire1 is arranged with an unmagnetized steel needle within it1 so that the discharge of a large ,leyden jar may take place through the coil1 the needle will be found strongly magnetic after the discharge of the electricity4 7,fig4 #aid47 ,many years before this was known1 it had been noticed that when a ship was struck by lightning1 the compasses were generally reversed2 and in a special case1 where a house was struck1 the electricity entered a box of knives1 fusing some1 tearing the handles off others1 but leaving them strongly magnetic4 ,electricians tried to repeat the effect by sending the discharge of powerful ,leyden batteries through bars of steel without any important result2 and it was not until ,oersted1 in the year #ahai1 made his important discovery that the copper wire conveying the electricity possessed peculiar magnetic power1 that the principle began to be understood1 and then the electricians succeeded in imitating the effects of lightning on steel1 as already described in the beginning of this chapter4 7,fig4 #aid47 ,illustration3 ,fig4 #aid4 ,a ,a4 ,a glass tube supported on two uprights of wood1 with coil of copper wire passing round it1 terminating in the balls ,b ,b4 ,c4 ,needle to place inside glass tube4 ,illustration3 ,fig4 #aie4 ,when the electricity has passed away from the ,leyden jar through the coil of ,page #bjg copper wire1 it no longer possesses any power to affect a piece of steel or iron1 but if the wires of the voltaic battery are now connected with the coil of copper wire1 which should be covered with cotton or silk1 and many yards in length1 then a bar of steel or soft iron is not only rendered magnetic1 but remains permanently so1 as long as the current of electricity continues to pass along the coil of wire1 so that if some nails or iron filings are brought to the bar of iron1 one end of which projects from the coil1 they cling to it with great force1 and a great number of nails may be hung on in this manner1 but they immediately fall off when the contact is broken with the battery4 7,fig4 #aie47 ,electricity thus becomes a source of magnetism1 and the discoverer1 ,oersted1 found that only needles or bars of steel or iron were thus affected1 and not those of brass1 shell-lac1 sulphur1 and other substances2 he termed the conducting wire a conjunctive wire1 and described the effect of the electric current or electric conflict1 as he called it1 as resembling a ,helix 7from ,greek3 heliss1 to turn round2 a screw or spiral71 and that it is not confined to the conducting wire1 but radiates an influence at some distance4 ,this latter statement is exactly in accordance with our present notions1 and hence the coil conveying the current is said to induce magnetism in the iron or steel1 just as the phenomena of induction are produced with frictional electricity4 ,the effect of ,oersted's discovery1 says ,silliman1 was truly electric2 the scientific world was ripe for it1 and the truth he thus struck out was instantly seized upon by ,arago1 ,ampre1 ,davy1 ,faraday1 and a crowd of philosophers in all countries4 ,the activity with which this new field of research has been cultivated1 has never relaxed even to this hour1 while it has borne fruit in a multitude of theoretical and practical truths1 and above all1 in the electro-magnetic telegraph1 truly called1 and especially in connexion with the ,atlantic telegraph wire1 the great international nerve of sensation4 ,illustration3 ,fig4 #aif4 ,a loadstone mounted in brass or silver1 with the iron cheeks ,b ,b attached4 ,c4 ,the bit of soft iron called the armature4 ,magnetism is not only the result of a current of electricity through any good conductor1 but there are certain oxides of iron1 called magnetic iron ores1 which have the property of attracting iron filings1 and are mostly found in primitive rocks1 being abundant at ,roslagen1 in ,sweden1 and called the loadstone1 from its always pointing1 when freely suspended1 to the ,polar1 ,north1 or ,load ,star4 ,if a tolerably large specimen of this mineral is examined1 there will be found usually two points where the iron filings are attracted in larger quantities than in other parts of the same specimen4 ,these attractive points are called poles1 and the loadstone being properly mounted with soft iron bars1 termed cheeks1 bound round it 7in old-fashioned loadstones7 with silver plate and duly ornamented with ,page #bjh engraving1 has its magnetic power greatly increased1 and is then said to be endowed with magnetic polarity2 and to prevent the loss of power1 a soft piece of iron1 called the armature1 is placed across and attracted to the poles of the loadstone4 7,fig4 #aif47 ,second ,experiment4 ,if a needle of tempered steel 7fitted with a little brass cup in the centre to work upon a point7 is rubbed with the loadstone in one direction only1 it is rendered permanently magnetic1 and will now be found to take a certain fixed position1 pointing always in a direction due north and south4 ,the end which points towards the north is called the north pole1 and the other extremity the south pole1 and it is usual to mark the north pole with an indent or scratch to distinguish it at all times4 ,third ,experiment4 ,if another bar of steel is magnetized1 and the north pole duly marked1 and then brought towards the same pole of the suspended magnet1 instant repulsion takes place2 the magnet1 of course1 grasped in the hand is not free to move1 but the small magnet immediately shows the same fact noticed with electricity1 viz41 that similar magnetisms repel4 ,two north poles repel each other1 but when the bar of steel is reversed1 the opposite effect occurs1 and the suspended magnet is attracted1 showing that dissimilar magnetisms attract1 and a north will attract a south pole4 7,fig4 #aig47 ,illustration3 ,fig4 #aig4 ,a magnetic needle1 the north pole ,n being attracted to the south pole of the bar magnet ,s1 and repelled from the north end4 ,fourth ,experiment4 ,illustration3 ,fig4 #aih4 ,the horse-shoe magnet1 and another one unmagnetized1 placed end to end2 the one shaded and lettered ,n and ,s is the magnet4 ,a ,a4 ,the piece of soft iron moved in the direction of the arrow4 ,by contact1 the magnetic power is transferred from the magnet to a piece of unmagnetized steel1 and it is stated that the highest magnetizing effect is that produced by the simple method of ,jacobi4 ,a horse-shoe magnet has its poles brought in contact with the intended poles of another bar of steel1 likewise bent in the form of a horse-shoe1 and by ,page #bji drawing the feeder over the unmagnetized horse-shoe in the direction of the arrow in the cut1 and when it reaches the curve1 bringing it back again to the same place1 say at least twelve times1 and after turning the whole over without separating the poles1 and repeating the same operation on the other side likewise twelve times1 the steel is then powerfully magnetized2 and it is said that a horse-shoe of one pound weight may be thus charged so as to sustain twenty-six and a half pounds1 and that by the old method of magnetizing it would only have sustained about twenty-two pounds4 7,fig4 #aih47 ,fifth ,experiment4 ,if the horse-shoe magnet is placed on a sheet of paper1 and some iron filings are dusted between the poles1 a very beautiful series of curves are formed1 called the magnetic curves1 which indicate the constant passage of the magnetic power from pole to pole4 ,sixth ,experiment4 ,the magnetic force exerted by a horse-shoe-shaped piece of soft iron1 surrounded with many strands of covered copper wire in short lengths1 is extremely powerful 7,fig4 #aii71 and enormous weights have been supported by an electro-magnet when connected with a voltaic battery4 ,supposing a man were dressed in complete armour1 he might be held by an electro-magnet1 without the power of disengaging himself1 thus realizing the fairy story of the bold knight who was caught by a rock of loadstone1 and1 in full armour1 detained by the unfriendly magician4 ,illustration3 ,fig4 #aii4 ,a4 ,powerful electro-magnet supporting a great weight4 ,b4 ,the battery4 ,page #baj ,seventh ,experiment4 ,when a piece of soft iron is held sufficiently near one of the poles of a powerful magnet1 it becomes by induction endowed with magnetic poles1 and will support another bit of soft iron1 such as a nail1 brought in contact with it4 ,when the magnet is removed1 the inductive action ceases1 and the soft iron loses its magnetic power4 ,this experiment affords another example of the connexion between the phenomena of electricity and magnetism4 ,it is in consequence of the inductive action of the magnetism of the earth that all masses of iron1 especially when they are perpendicular1 are found to be endowed with magnetic polarity2 hence the reaction of the iron in ships upon the compasses1 which have to be corrected and adjusted before a voyage1 or else serious errors in steering the vessel would occur1 and there is no doubt that many shipwrecks are due to this cause4 ,no other metals beside iron1 steel1 nickel1 cobalt1 and possibly manganese1 can receive or retain magnetism after contact with a magnet4 ,the remarkable effect of magnetism upon all matter1 so ably investigated by ,faraday and others1 will be explained in another part of this book--viz41 in the article on ,dia-,magnetism4 ,illustration3 ,fig4 #bjj4 ,magician and his loadstone-rock4--,vide ,fairy ,tale4 ,page #baa ,,chapter ,,xvi4 ,,electro-,,magnetic ,,machines4 ,the experiments already described in illustration of some of the phenomena of electro-magnetism are of such a simple nature that they may be comprehended without difficulty2 but it is not such an easy task to appreciate the curious fact of an invisible power producing motion4 ,it has already been explained that a copper or other metallic wire conveying a current of electricity becomes for the time endowed with a magnetic power1 and if held above1 or below1 or close to1 a suspended magnetized steel needle1 affects it in a very marked degree1 causing it to move to the right or left1 according to the direction of the electric current2 and in order to form some notion of the condition of a metallic wire whilst the electricity is passing through it1 the annexed diagrams may be referred to4 7,figs4 #bja1 #bjb47 ,illustration3 ,fig4 #bja4 ,portion of a square copper conductor1 in which ,a ,b represents the direction of the electricity1 and the small arrows1 ,c ,c ,c ,c1 the magnetic current or whirl at right angles to the electrical current1 and exercising a tangential action4 ,illustration3 ,fig4 #bjb4 ,a round conducting wire1 in which the electrical current is flowing in the direction of the large dart ,a ,b1 and the small arrows indicate the direction of the magnetic force4 ,dr4 ,roget says3 ,the magnetic force which emanates from the electrical conducting wire is entirely different in its mode of operation from all other forces in nature with which we are acquainted4 ,it does not act in a direction parallel to that of the current which is passing along the wire1 nor in any plane passing through that direction4 ,it is evidently exerted in a plane perpendicular to the wire1 but still it has no tendency to move the poles of the magnet in a right or radial line1 either directly towards1 or directly from1 the wire1 as in every other case of attractive or repulsive agency4 ,the peculiarity of its action is that it produces motion in a circular direction all round the wire--that is1 in a direction at right angles to the radius1 or in the direction of the tangent to a circle described round the wire in a plane perpendicular to it2 hence the electro-magnetic force exerts a tangential action1 or that which ,dr4 ,wollaston called a vertiginous or whirling motion4 ,page #bab ,dr4 ,faraday concluded that there is no real attraction or repulsion between the wire and either pole of a magnet1 the action which imitates these effects being of a compound nature2 and he also inferred that the wire ought to revolve round a magnetic pole of a bar magnet1 and a magnetic pole round a wire1 if proper means could be devised for giving effect to these tendencies1 and for isolating the operations of a single pole4 ,for the first idea of electro-magnetic rotation the world is indebted to ,dr4 ,wollaston2 but ,dr4 ,faraday1 with his usual ingenuity1 was the first who carried out the theory practically4 ,the rotation of a wire 7conveying a current of voltaic electricity7 round one of the poles of a magnet is well displayed with the simple contrivance devised by him4 7,fig4 #bjc47 ,illustration3 ,fig4 #bjc4 ,n4 ,a small bar magnet cemented into a wine-glass1 the north pole being at ,n4 ,a is a moveable wire looped over the hook1 which is the positive 77 pole of the battery2 the free extremity rotates round the pole of the magnet when the current of electricity passes4 ,the dotted line represents the level of the mercury which the glass contains4 ,the electricity passes in at ,a1 and out at the wire ,b1 as shown by the arrows4 ,c is connected with the negative1 and ,d with the positive1 pole of the battery4 ,by a careful observation of the complex action of an electrified wire upon a magnetic needle1 ,dr4 ,faraday was enabled to analyse the phenomena with his usual penetration and exhaustive ability1 and he found1 as ,daniell relates1-- ,that if the electrified wire is placed in a perpendicular position1 and made to approach towards one pole of the needle1 the pole will not be simply attracted or repelled1 but will make an effort to pass off on one side in a direction dependent upon the attractive or repulsive power of the pole2 but if the wire be continually made to approach the centre of motion by either the one or the other side of the needle1 the tendency to move in the former direction will first diminish1 then become null1 and ultimately the motion will be reversed1 and the needle will principally endeavour to pass in the opposite direction4 ,the opposite extremity of the needle will present similar phenomena in the opposite direction2 hence ,dr4 ,faraday drew the conclusion that the direction of the forces was tangential to the circumference of the wire1 that the pole of the needle is drawn by one force1 not in the direction of a radius to its centre1 but in that of a line touching its circumference1 and that it is repelled by the other force in the opposite direction4 ,in this manner the northern force acted all round the wire in one direction1 and the southern in the opposite one4 ,each pole of the needle1 in short1 appeared to have a tendency to revolve round the wire in a direction opposite to the other1 and1 consequently1 the wire round the poles4 ,each pole has the power of acting upon the wire by itself1 and not as connected with the opposite pole1 and the apparent attractions and repulsions are merely exhibitions of the revolving motions in different parts of their circles4 ,page #bac ,the same fact illustrated at ,fig4 #bjc1 is also demonstrated in a still more striking manner by means of wire bent into a rectangular form1 and so arranged that whilst the current of electricity passes1 it is free to move in a circle2 and when the poles of a magnet are brought towards the electrified wire1 it may be attracted or repelled at pleasure1 and in fact becomes a magnetic indicator1 and places itself 7if carefully suspended7 at right angles to the magnetic meridian4 7,fig4 #bjd47 ,illustration3 ,fig4 #bjd4 ,a ,a ,a ,a4 ,the rectangular wire covered with silk and varnished1 one end of which being pointed1 rests on the little cup ,b1 connected with a covered wire passing down the centre of the brass support to the binding screw ,c let into ivory4 ,d4 ,the other extremity of the rectangular wire2 this being covered and varnished1 is not in metallic contact with the end ,b1 but is likewise pointed1 and dips into the mercury contained in the large cup ,e ,e4 ,the upper and lower cups do not touch1 and are separated by ivory1 marked by the shaded portion1 and the cup ,e ,e is in metallic communication with the brass pillar1 and is connected with the negative pole of the battery at ,f1 whilst ,c is connected with the positive pole of the battery1 and the electricity circulates round the wire in the direction of the arrows4 ,when a bar magnet1 ,n1 is brought towards the wire1 the latter is immediately set in motion1 and by alternately presenting the opposite poles of the magnet1 the rectangular wire rotates freely round the cup ,b4 ,these curious movements of a magnetized needle1 and rotations of wires and magnets1 brought about by the agency of an active current of electricity1 have induced ,sir ,david ,brewster to advance his admirable theory1 which supposes the affection of the mariner's compass needle1 and all other suspended pieces of steel1 to be due to the agency of electrical currents continually circulating around the globe2 and ,mr4 ,barlow contrived the following experiment in illustration of ,brewster's theory4 ,a wooden globe1 sixteen inches in diameter1 was made hollow1 for the purpose of reducing its weight1 and while still in the lathe1 grooves one-eighth of an inch deep and broad were cut to represent an equator1 and parallels of latitude at every four and a half degrees each way from the equator to the poles4 ,a groove of double depth was also cut like a meridian from pole to pole1 but only half round4 ,the grooves were cut to receive the copper wire covered with silk1 and the laying on was commenced by taking the middle of a length of ninety feet of wire one-sixteenth of an inch in diameter1 which was applied to the equatorial groove so as to meet in the transverse meridian2 it was then made to pass round this parallel1 returned again along the meridian to the next parallel1 and then passed round this again1 and so on1 till the wire was thus led in continuation from pole ,page #bad to pole4 ,the length of wire still remaining at each pole was returned from each pole along the meridian groove to the equator1 and at this point1 each wire being fastened down with small staples1 the wires from the remaining five feet were bound together near their common extremity1 when they opened to form separate connexions for the poles of a voltaic battery4 ,when the battery was connected1 and magnetic needles placed in different positions1 they behaved precisely as they would do on the surface of the earth1 the induction set up by the electrified wire being a perfect imitation of that which exists on the globe4 ,the opposite effect to that already described--viz41 the rotation of one pole of a magnet round the electrified wire1 was also arranged by ,faraday in the following manner4 7,fig4 #bje47 ,illustration3 ,fig4 #bje4 ,n ,s4 ,a little magnet floating in mercury contained in the glass ,a ,a2 the north pole is allowed to float above the surface of the quicksilver1 and the south pole is attached to the wire passing through the bottom of the glass vessel4 ,the electricity passes in at ,b1 and taking the course indicated by the arrows travels through the glass of quicksilver to the other pole of the battery at ,c4 ,directly contact is made with the battery1 the little magnet rotates round the electrified wire1 ,w4 ,the dotted line shows the level of the mercury in glass4 ,in the examination of the magnetic phenomena obtained from wires transmitting a current of electricity1 it should be borne in mind that any conducting medium which forms part of a closed circuit--i4e41 any conductor1 such as charcoal1 saline fluids1 acidulated water1 which form a link in the endless chain required for the path of the electricity1--will cause a magnetic needle placed near it to deviate from its natural position4 ,these positions of the electrified wire and the magnetic needle are of course almost unlimited1 and in order to assist the memory with respect to the fixed laws that govern these relative movements1 ,monsieur ,ampre has suggested a most useful mechanical aid1 and he says3--,let the observer regard himself as the conductor1 and suppose a positive electric current to pass from his head towards his feet1 in a direction parallel to a magnet2 then its north pole in front of him will move to his right side1 and its south pole to his left4 ,the plane in which the magnet moves is always parallel to the plane in which the observer supposes himself to be placed4 ,if the plane of his ,page #bae chest is horizontal1 the plane of the magnet's motion will be horizontal1 but if he lie on either side of the horizontally-suspended magnet1 his face being towards it1 the plane of his chest will be vertical1 and the magnet will tend to move in a vertical plane4 ,this very lucid comparison will be seen to apply perfectly to the direction of the rotations in ,figs4 #bjc and #bje4 ,the whole of this apparatus is made in the most elegant and finished manner by ,messrs4 ,elliott1 of #cj1 ,strand2 and by a modification of the latter arrangement 7,fig4 #bjf71 the opposite rotations of the opposite poles of the magnets round the electrified wire1 are shown in the most instructive manner4 ,the apparatus 7,fig4 #bjf7 was devised by the late ,mr4 ,francis ,watkins1 and consists of two flat bar magnets doubly bent in the middle1 and having agate cups fixed at the under part of the bend 7by which they are supported7 upon upright pointed wires1 the latter being fixed upright on the wooden base of the apparatus1 and the magnets turn round them as upon an axis4 ,illustration3 ,fig4 #bjf4 ,a4 ,wire conveying the current of electricity4 ,b ,b4 ,the magnets balanced on points rotating round the wires4 ,two circular boxwood cisterns1 to contain quicksilver1 are supported upon the stage or shelf above the base4 ,a bent pointed wire is directed into the cup of each magnet1 the ends of which dip into the mercury contained in the boxwood circular troughs on the stage4 ,by using a battery to each magnet1 and taking care that the currents of electricity flow precisely alike1 they will then rotate in opposite directions4 ,directly after the ingenious experiments of ,faraday became known1 a great number of electro-magnetic engine models were constructed1 and many thought that the time was fast approaching when steam would be superseded by electricity2 and really1 to see the pretty electro-magnetic models work with such amazing rapidity1 it might be supposed that if they were constructed on a larger scale1 a great amount of hard work could be obtained from them4 ,this idea1 however1 has been proved to be a fallacy1 for reasons that will be presently explained4 ,the figure on p4 #baf displays two of these engines1 one of which represents the rotation of electro-magnets within four fixed steel magnets1 and the other the rotation of steel magnets by the fixed electro-magnets4 ,the latter 7,no4 #b7 moves with such great velocity1 that unless the strength of the battery is carefully adjusted1 the connexions are soon destroyed4 7,fig4 #bjg47 ,page #baf ,illustration3 ,fig4 #bjg4--,no4 #a consists of vertical permanent steel magnets and horizontal soft-iron electro-magnets which rotate4 ,no4 #b consists of two fixed soft-iron electro-magnets1 and four bent permanent steel magnets1 which rotate1 in both cases of course1 only when connected with the battery4 ,considering the prodigious power or pull of a soft-iron electro-magnet1 and its capability of supporting considerable weight1 the most reasonable expectations of success might be entertained with machines acting by the direct pull4 ,it was1 however1 discovered that they soon became inefficient1 from the circumstance that the repeated blows received by the iron so altered its character1 that it eventually assumed the quality of steel1 and had a tendency to retain a certain amount of permanent magnetism1 and thus to interfere with the principle of making and unmaking a magnet4 ,it was this fact that induced ,professor ,jacobi1 of ,st4 ,petersburg1 after a large expenditure of money1 to abandon arrangements of this kind1 and to employ such as would at once produce a rotatory motion4 ,the engine thus arranged was tried upon a tolerably large scale on the ,neva1 and by it a boat containing ten or twelve people was propelled at the rate of three miles an hour4 ,various engines have been constructed by ,watkins1 ,botta1 ,jacobi1 ,armstrong1 ,page1 ,hjorth2 the engine made by the latter 7,hjorth7 excited much attention in #ahea-eb1 and consisted of an electro-magnetic piston drawn within or repelled from an electro-magnetic cylinder2 and by this motion it was thought that a much greater length of stroke could be secured than by the revolving wheels or discs1 but the loss of power 7not only in this engine1 but in others7 through space is very great1 and the lifting power of any magnet is greatly reduced and ,page #bag altered at the smallest possible distance from its poles4 ,this loss of power is therefore a great obstacle in the way of the useful application of electro-magnetic force1 and can be appreciated even with the little models1 all of which may be stopped with the slightest friction1 although they may be moving at the time with great velocity4 ,in the second place1 supposing the reduced force exerted by the two magnets1 a few lines apart1 was considered available for driving machinery1 the moment the magnets begin to move in front of one another there is again a great loss of power1 and as the speed increases1 there is curiously a corresponding diminution of available mechanical power1 a falling-off in the duty of the engine as the rotations become more rapid4 ,in the third place1 the cost of the voltaic battery1 as compared with the consumption of coal in the steam-engine1 is very startling1 and extremely unfavourable to electro-magnetic engines4 ,mr4 ,j4 ,p4 ,joule found that the economical duty of an electro-magnetic engine at a given velocity and for a given resistance of the battery is proportioned to the mean intensity of the several pairs of the battery4 ,with his apparatus1 every pound of zinc consumed in a ,grove's battery produced a mechanical force 7friction included7 equal to raise a weight of #cca1djj pounds to the height of one foot1 when the revolving magnets were moving at the velocity of eight feet per second4 ,now1 the duty of the best ,cornish steam-engine is about one million five hundred thousand pounds raised to the height of one foot by the combustion of each pound of coal1 or nearly five times the extreme duty that could be obtained from an electro-magnetic engine by the consumption of one pound of zinc4 ,this comparison is therefore so very unfavourable1 that the idea of a successful application of electricity as an economic source of power1 is almost1 if not entirely abandoned4 ,by instituting a comparison between the different means of producing power1 it has been shown that for every shilling expended there might be raised by ,pounds4 ,manual power #fjj1jjj one foot high in a day4 ,horse #c1fjj1jjj ,steam #ef1jjj1jjj ,electro-magnetism #ijj1jjj ,a powerful magnet has been compared to a steam-engine with an enormous piston but with an exceedingly short stroke4 ,although motive power cannot be produced from electricity and applied successfully to commercial purposes1 like the steam-engine1 yet the achievements of the electric telegraph as an application of a small motive power must not be lost sight of1 whilst the fall of the ball at ,deal and other places1 by which the chronometers of the mercantile navy are regulated1 as also the means of regulating the time at the ,general ,post ,office and various railway stations1 are all useful applications of the power which fails to compete in other ways with steam4 ,page #bah ,,chapter ,,xvii4 ,,the ,,electric ,,telegraph4 ,the engineering and philosophical details of this important instrument have grown to such formidable dimensions1 that any attempt 7short of devoting the whole of these pages to the subject7 to give a full account of the history and application of the instrument1 the failures and successes of novel inventions1 and the continued onward progress of this mode of communication1 must be regarded as simply impossible1 and therefore a very brief account of the principle only will be attempted in these pages4 ,for the complete history of the discovery and introduction of the principle of the ,electric ,telegraph the reader is referred to the ,society of ,arts ,journal 7,nos4 #cdh-i1 vol4 viii471 where it is stated that it is half a century1 dating from ,august1 #ahei1 since the first galvanic telegraph was made4 ,it was the ,russian ,baron ,schilling's electro-magnetic telegraph which1 without its being known to be his1 was brought to ,london1 and caused the establishment of the first practically useful telegraph lines1 not only in ,great ,britain1 but in the world4 ,dr4 ,hamel says3 ,the small sprout nursed on the ,neva1 which had been exhibited on the ,rhine1 and thence brought to the ,thames1 grew up here to a mighty tree1 the fruit-laden branches of which1 along with those from trees grown up since1 extend more and more over the lands and seas of the ,eastern hemisphere1 whilst kindred trees planted in the ,western hemisphere have covered that part of the world with their branches1 some of which will1 ere long1 be interwoven with those in our hemisphere4 ,the first telegraph line in ,england was constructed by ,mr4 ,cooke from ,paddington along the ,great ,western ,railroad to ,west ,drayton in #ahch-ci2 and it must be remembered that it was in ,february1 #ahcg1 that ,mr4 ,cooke first consulted ,professor ,charles ,wheatstone1 having previously visited ,dr4 ,faraday and ,dr4 ,roget1 and on the #aith ,november1 #ahcg1 a partnership contract was concluded between ,messrs4 ,cooke and ,wheatstone4 ,to the distinguished philosopher1 ,professor ,wheatstone1 the merit of the ingenious construction of the vertical-needle telegraph is due2 whilst ,mr4 ,cooke's name will always be associated with the practical establishment of the first telegraph lines in ,england4 ,the first line in the ,united ,states1 from ,washington to ,baltimore1 was completed in #ahdd1 being arranged and worked by ,professor ,morse4 ,in ,british ,india1 in ,april and ,may1 #ahci1 the first long line of telegraph1 twenty-one miles in length1 and embracing #gjjj feet of river surface1 was constructed by ,dr4 7now ,sir ,william7 ,o',shaughnessy4 ,page #bai ,the construction of the electric telegraph may be considered under three heads3 #ast4 ,the ,battery1 the motive power4 #bnd4 ,the ,wires1 the carriers of the force4 #crd4 ,the ,instruments to be worked--the bell and the needle telegraph4 ,,the ,,battery4 ,the construction and rationale of the batteries generally in use have been explained in another part of this work2 those used for telegraphic purposes consist of one or more couples1 of which zinc is one1 the second being copper1 silver1 platinum1 or carbon4 ,each couple is termed an element1 and a series of such couples a battery4 ,the batteries employed chiefly on the ,english lines consist of a plate of cast-zinc four inches square and #c_/afths of an inch thick1 attached by a copper strap one inch broad to a thin copper plate four inches square4 ,the zinc is well amalgamated with mercury4 ,twelve of these couples are arranged in a trough of wood1 porcelain1 or gutta-percha1 divided by partitions into twelve water-tight cells1 #a inch wide4 ,the zinc and copper preserve the same order and direction throughout1 and when arranged1 the trough is filled with the finest white sand1 and then moistened with water previously mixed with five per cent4 by measure of pure sulphuric acid4 ,this mode of applying the acid is the clever practical improvement of ,mr4 ,cooke1 and prevents any inconvenience from the spilling of the acid1 and at the same time renders the battery quite portable4 ,the voltaic arrangement thus prepared is found to remain in action for several weeks1 or even months1 with the occasional addition of small quantities of acid1 and answers well for working needle telegraphs in fine and dry weather4 ,in fogs and rains1 at distances exceeding #bjj miles at most1 their action is not so perfect1 and a vast number of couples must be employed1 #add to #bhh being frequently in use4 ,in ,france1 ,prussia1 and ,america1 sand batteries do not appear to answer1 and ,daniell's arrangement is preferred4 ,sixty couples suffice in ,france for some of the long lines--viz41 from ,paris to ,bordeaux1 #bhd miles2 ,paris to ,brussels1 #bca miles2 and in fact1 the advantages of the ,daniell's battery have become so apparent1 that they are now being used on ,english lines4 ,in ,prussia1 ,bunsen's carbon battery is much used2 in ,india1 a modification of ,grove's battery is preferred1 the zinc being acted upon by a solution of common salt in water4 ,two of these elements were found sufficient to work a line of forty miles totally uninsulated1 and including the sub-aqueous crossing of the ,hooghly ,river1 #fbjj feet wide4 ,the continual energy of the battery1 whatever may be its construction1 depends on the circulation of the electricity1 the object being to pass the force from the positive end of the series through the wires1 back again to the negative extremity of the voltaic series4 ,the wire 7the carrier of the force7 must be continuous throughout1 unless1 of course1 water or earth forms a part of the endless conducting chain4 ,page #bbj ,,the ,,conducting ,,wires4 ,these roads for the electricity may be of any convenient metal1 and the one preferred and used is iron1 which is well calculated from its great tenacity 7being the most tenacious metal known7 and cheapness to convey the electricity1 although it is not such a good conductor as copper1 and offers about six times more resistance to the flow of the current than the latter metal4 ,the wire does not appear to be made of iron1 because it is galvanized or passed through melted zinc1 which coats the surface and defends it from destructive rust1 at the same time does not destroy its valuable property of tenacity or power of resisting a strain4 ,about one ton of wire is required for every five miles1 and to support this weight1 stout posts of fir or larch are erected about fifty yards apart1 and from ten to twenty-five feet high4 ,at every quarter mile1 on many lines1 are straining-posts with ratchet wheel winders1 for tightening the wires4 ,on some of the lines the wires are attached to the posts by side brackets carrying the insulators invented by ,mr4 ,c4 ,v4 ,walker1 which are composed of brown salt-glazed stoneware of the hour-glass shape1 as shown in the drawing4 7,fig4 #bjh47 ,illustration3 ,fig4 #bjh4 ,walker's insulator4 ,there are some objections to the hour-glass insulators1 and they have been modified by ,mr4 ,edwin ,clark1 ,page #bba who employs a very strong stone-ware hook open at the side1 so that the wire can be placed on the hook without threading1 and the hooks can be replaced in case of breaking1 without cutting the telegraph wire1 which is securely fastened to each insulator by turns of thinner wire4 ,an inverted cap of zinc is used to keep the insulator dry4 7,fig4 #bji47 ,illustration3 ,fig4 #bji4 ,clark's insulator4 ,in ,india the conductor is rather a rod than a wire1 and weighs about half a ton per mile2 it is erected in the most substantial manner1 and many miles of the rod are supported on granite columns1 other portions on posts of the iron-wood of ,arracan1 or of teak4 ,the number of wires required by the electric telegraph often puzzles the railway traveller1 and people ask why so many wires are used on some lines and so few on others8 ,the answer is very simple3 they are for convenience4 ,two wires only are required for the double needle telegraph1 and one for the single needle instrument4 ,but as so many instruments are required at the terminal stations1 an increased number of wires1 like rails for locomotives1 must be provided2 thus1 on the ,eastern ,counties1 seven wires are visible1 and are thus employed4 ,the two upper wires pass direct from ,london to ,norwich2 the next pair connect ,london1 ,broxbourne1 ,cambridge1 ,brandon1 ,chesterfield1 ,ely2 the third pair all the small stations between ,london and ,brandon2 and the seventh wire is entirely devoted to the bell4 ,if the earth was not a conductor of electricity1 and employed in the telegraphic circuit1 four wires would be required for the double needle telegraph1 and two for the single instrument4 ,to understand this1 let us suppose a battery circuit extending from ,paddington to the instrument at ,slough1 and the wire returning from ,slough to ,paddington1 it is evident that one wire would take the electricity to ,slough1 and the other return it to ,london1 as in the diagram below4 7,fig4 #baj47 ,illustration3 ,fig4 #baj4 ,a4 ,the battery4 ,b4 ,the instrument4 ,the arrows show the passage of the electricity to the single needle telegraph instrument by one wire1 and the return current by the other4 ,if the whole of the return wire is cut away except a few feet at each end1 which are connected by plates of copper with the damp earth1 the current not only passes as before1 but actually has increased in intensity1 and will cause a much more energetic movement of the needle in the telegraph instrument4 7,fig4 #baa47 ,these plates are called ,earth ,plates2 and ,steinheil1 in #ahcg1 was the first who proved that the earth might perform the function of a wire4 ,page #bbb ,illustration3 ,fig4 #baa4 ,a4 ,the battery4 ,b4 ,the instrument4 ,c4 ,earth plate at ,slough4 ,d4 ,earth plate at ,london4 ,the arrows show the direction of the electric current4 ,it must be obvious that a message may be received at any station without a battery1 but in order to be able to return an answer1 every station must have its own battery4 ,ingeniously-constructed lightning-conductors are attached to the posts which carry the wires1 so that in case of a storm1 the natural electricity is conveyed to the earth1 whilst the voltaic electricity artificially produced pursues its own course without deviation4 ,protectors are also required for the instruments at the stations1 and the plan devised by ,mr4 ,highton is thus described by the inventor3-- ,a portion of the wire circuit--say for six or eight inches--is enveloped in blotting-paper or silk1 and a mass of metallic filings1 in connexion with the earth1 is made to surround it4 ,this arrangement is placed on each side of the telegraph instrument at a station4 ,when a flash of lightning happens to be intercepted by the wires of the telegraph1 the myriads of infinitesimally fine points of metal in the filings surrounding the wire at the station1 on having connexion with the earth1 at once draw off nearly the whole charge of lightning1 and carry it safely to the earth4 ,,the ,,instruments ,,to ,,be ,,worked--,,the ,,bell ,,and ,,the ,,telegraph4 ,the bell or alarum resembles in construction that of an ordinary clock1 and is in fact a piece of clockwork wound up and ready to ring a bell1 when the detent or preventive is removed4 ,the detent is connected with a piece of soft iron placed before an electro-magnet1 and directly the current passes1 the electro-magnet attracts the soft piece of iron attached to a perpendicular lever which the bell-crank lever rests upon2 the detent is removed1 and the bell rings1 and again stops when the current of electricity ceases to pass4 ,one of the most simple alarum clocks is a common ,american clock1 wound up daily4 ,a small electro-magnet surrounded with thick wire is placed below a moveable piece of tinned iron1 so that when this is attracted1 the fly of the clock is released1 and its bell tolls unceasingly while ,page #bbc the magnet is excited4 ,this arrangement is employed by ,sir ,w4 ,o',shaughnessy in the ,indian telegraph system4 7,fig4 #bab47 ,it will readily be comprehended from this description that the alarum is sounded by ordinary mechanism1 and that the duty of the current of the electricity is simply comprised in the act of removing the lever and liberating machinery1 which may be large or small2 and if it were thought necessary1 the bells of the great clock-tower of the ,houses of ,parliament1 which chime the quarters1 or even ,big ,ben himself 7when his constitution is restored71 could be rung by a person at ,york or ,edinburgh1 supposing wires1 batteries1 and a powerful electro-magnet with a detent mechanism for the bells1 were properly arranged and connected with the clockwork4 ,illustration3 ,fig4 #bab4 ,a4 ,the soft iron tinned1 which is attracted to the electro-magnet ,b1 and liberates the detent4 ,in certain cases1 ,mr4 ,charles ,v4 ,walker states that a single and distinct wire is used for the bell only1 with his special mechanism1 called the ringing key4 ,if the bell was always on the same wire as the needle-coil1 the bell would not only call the attention of1 but seriously annoy the clerk 7unless1 of course1 he happened to be a very deaf person7 by its ringing whilst he was reading the signals of the needle4 ,the nuisance is prevented by what is termed joining over or making the short circuit--in fact1 by providing for the current a shorter and much more capacious road to the needle coil than by going through that of the bell-magnet1 which is made with very fine wire2 and the control of the short circuit is put in the hands of the clerk4 ,,cooke ,,and ,,wheatstone',s ,,double ,,needle ,,telegraph4 ,the principle of this instrument1 as already explained1 is involved in the elementary experiment of ,oersted--viz41 the deflection of a magnetic needle from the inside of a coil of wire conveying a current of electricity1 and as it is difficult to give a good description and drawing of the interior of the instrument that can really be understood1 it may be sufficient to state that the handles give the operator the power of reversing the current of electricity1 so that the needles are deflected with the utmost certainty to ,page #bbd one side or the other1 either separately or simultaneously4 7,fig4 #bac47 ,illustration3 ,fig4 #bac4 ,the letters of the alphabet1 figures1 and a variety of conventional signals1 are indicated by the single and combined movements of the needles on the dial4 ,the left-hand needle moving once to the left indicates the 1 which is given at the end of a word4 ,twice in the same way1 ,a2 thrice1 ,b2 first right1 then left1 ,c2 the reverse1 ,d4 ,once direct to the right1 ,e2 twice1 ,f2 thrice1 ,g4 ,in the same order with the other needle for ,h1 ,i1 ,k1 ,l1 ,m1 ,n1 ,o1 ,p4 ,the signals below the centre of the dial are indicated by the parallel movements of both needles simultaneously4 ,both needles moving once to the left indicate ,r2 twice1 ,s2 thrice1 ,t4 ,first right1 then left with both1 ,u2 the reverse1 ,v4 ,both moving once to the right1 ,w2 twice1 ,x2 thrice1 ,y4 ,the figures are indicated in the same way as the letters nearest to which they are respectively placed4 ,to change from letters to figures the operator gives ,h1 followed by the 1 which the recipient returns to signify that he understands4 ,if1 after the above signs 7,h and 7 were given1 ,c ,r ,h ,l were received1 #ahde would be understood4 ,a change from figures to letters is notified by giving ,i1 followed by the 1 which the recipient also returns4 ,each word is acknowledged4 ,if the recipient understand1 he gives ,e2 if not1 the 1 in which case the word is repeated4 ,attention to a communication by this instrument is called by the ringing of a bell 7of any size71 which is effected through the agency of an electric current4 ,the upper case contains the bell4 ,sir ,w4 ,o',shaughnessy1 in his excellent work on the electric telegraph in ,british ,india1 gives a description of a telegraphic instrument of remarkable simplicity1 which is successfully employed in ,india1 and is ,page #bbe highly spoken of by ,mr4 ,e4 ,v4 ,walker and other gentlemen practically acquainted with the working of telegraphs4 ,it consists of a coil of fine wire on a card or ivory frame1 a magnetic needle with a light index of paper pasted across it2 two stops of thin sheet lead to limit the vibrations of the index2 a supporting board eight inches square1 and a square of glass in a frame of wood1 or a common glass tumbler placed over it as a shade1 to prevent the index being moved by currents of air4 ,it is stated that the office boys1 with the assistance of a native ,indian carpenter1 make up these telegraphs at a price not exceeding two shillings each4 ,in ,england of course they would be more expensive2 but the simplicity and perfection of the arrangement are so much to be commended that we give the details for the benefit of those boys who might wish to establish a telegraph on a small scale for amusement4 ,,the ,,frame4 ,this is a piece of mahogany eight inches square and one inch thick1 with a hollow groove cut in its centre two inches and a half long1 half an inch wide1 and a quarter of an inch deep2 a ledge of the same wood one inch wide and half an inch deep surrounds the frame1 leaving the inner surface seven inches square2 this is stained black with ink to make the motions of the index more conspicuous4 ,,the ,,coil4 ,this consists of fifty feet of the finest silk-covered copper wire wound on a frame of card two inches long1 half an inch broad1 three-eighths deep in the open part4 ,an edge or flange of card1 three-eighths of an inch wide1 is attached to it at each side to keep the wire in its place4 ,the frame may be of thin wood or ivory1 and the winding of the wire commences at the lower left corner1 and it is coiled from left to right1 as the hands of a watch would move in the same plane4 7,fig4 #bad47 ,illustration3 ,fig4 #bad4 ,the coil4 ,two inches of each end of the coil wire are now stripped of their silk covering by being rubbed with sand-paper4 ,the coil is mounted in the frame by inserting its lower edge or flange in the groove1 so that the lower part or floor of the inside of the coil is level with that of the ,page #bbf frame1 as shown below1 and it is now ready to receive the magnetized needle4 7,fig4 #bae47 ,illustration3 ,fig4 #bae4 ,the coil fitted into frame4 ,,the ,,needle4 ,this is one inch long1 one-twelfth of an inch wide1 of the thinnest steel1 and fitted with a little brass cap turned to a true cone to receive the point on which it is balanced4 ,these needles are of hard tempered steel1 and are magnetized by a single contact with the poles of an electro-magnet or other ordinary powerful magnet4 ,the magnet is now to be balanced on a steel point one-eighth of an inch high2 these are nipped off with cutting pliers from common sewing needles1 and soldered into a slip of thin copper three inches long1 half an inch wide4 7,fig4 #baf47 ,illustration3 ,fig4 #baf4 ,a4 ,the needle4 ,b4 ,the point on the slip of copper4 ,as the north end of the needle will be found to dip1 it is advisable to counteract this by touching the south end with a little shell-lac varnish1 which dries rapidly1 and soon restores the needle to a perfect equilibrium4 ,the needle is completed for use by fixing to it an index of paper 7cut from glazed letter paper7 two inches long1 tapering from one-eighth of an inch to a point1 and fastened at right angles on to the needle with lac varnish1 so as to be truly balanced1 and pointing the sharp end to the east1 when the needle placed on the point settles due north and south1 its north pole being opposite the observer's right hand1 the observer facing west4 7,fig4 #bag47 ,illustration3 ,fig4 #bag4 ,the needle with the paper index4 ,page #bbg ,the coil frame is placed north and south1 and the needle is now introduced by sliding the end of the slip of copper into the opening in the frame4 ,to limit the vibrations of the paper index a stop is placed at each side4 ,the stops are made of a strip of thin sheet-lead or copper1 a quarter of an inch broad1 one inch and a half long1 and turned up at a right angle1 so that one inch rests on the board and half an inch is vertical4 ,for ordinary practice these stops are placed each at half an inch from the index4 ,the telegraph is placed in a box1 which may have a piece of looking-glass in the lid1 so that the readings can be taken with the needle in the vertical instead of the horizontal position1 if required4 7,fig4 #bah47 ,illustration3 ,fig4 #bah4 ,box containing the telegraph1 with the looking-glass in the lid4 ,a small steel magnet is placed on or near the frame1 if required1 the south pole of this magnet being opposite to the north pole of the needle in the telegraph coil4 ,the bar is four inches long1 half an inch broad1 three-sixteenths of an inch thick1 and it is only used to counteract any local deviation which may arise in using the instrument with miles of wire4 ,it would not be required under ordinary circumstances4 ,the alphabet used is shown to the left4 ,the ends of the fine wire of the telegraph coil are joined on to the wires from the reversing instrument1 and this is connected with a voltaic series of one or more elements1 so that by the employment of the reverser the needle is caused to move right or left at pleasure4 ,the ,page #bbh white paper index on the black ground can be followed with the greatest certainty1 and ,sir ,w4 ,o',shaughnessy states that with this instrument a telegraph clerk may read at the rate of twenty words per minute with a double needle wire1 being equal to forty words per minute4 ,,the ,,reverser consists of a block of wood1 two inches and a half square1 in which four hollows1 half an inch deep1 are cut1 and these hollows are joined diagonally by copper wires let into the substance of the wood1 and most carefully insulated from each other by melted cement1 but exposing a clean metallic surface in each cell1 which is filled with mercury4 7,fig4 #bai47 ,illustration3 ,fig4 #bai4 ,block of wood with four holes2 the positive terminal is connected with the holes ,a and ,b1 the negative with ,c and ,d2 the hollows are filled with mercury4 ,t ,t are the wires from the telegraph box1 and it is obvious that by dipping them alternately into ,c ,b and ,a ,d the current is reversed1 and the needle deflected right or left at pleasure4 ,in practice a more elaborate reverser is employed1 but to demonstrate the principle the simple block above described is quite sufficient4 ,with the telegraph placed at the top of a house1 or in a distant cottage1 and a single cell of ,grove's battery1 or at most two1 for any short distances1 with the reverser1 messages may be passed with great rapidity from the bottom of the house to the top1 or from a mansion to the lodge1 it being understood that a battery1 reverser1 and telegraph1 are required at both places where messages are received and answered2 but if no answers are required1 the battery and reverser are placed at one end of the wire in the house1 and the telegraph at the other extremity in the cottage1 and earth plates may be arranged to return the current1 or another wire used for that purpose4 ,whilst lauding to the utmost the invention of the electric telegraph1 we must remember there is nothing new under the sun1 and that after all ,nature claims the principle of telegraphing1 and with the silent gesture1 the speaking eye1 interpreted and answered by others1 she proclaims herself to be the originator of communication by signs4 ,whilst ,page #bbi the language of flowers1 and the mournful requirements of the deaf and dumb in the use of the finger alphabet1 show how readily man has adopted the important principle1 till he has brought it to the highest state of perfection in the electric telegraph4 ,when the telegraph was first adopted on the ,great ,western ,railway1 the most ridiculous ideas were formed of its capabilities1 and many persons firmly believed that the wires were used for the purpose of dragging letters and different articles from station to station4 ,wife1 said a man1 looking at the telegraph wires1 ,i don't see1 for my part1 how they send letters on them wires1 without tearin' 'em all to bits4 ,oh1 you stupid6 exclaimed his intellectual spouse2 why1 they don't send the paper3 they just send the writin' in a fluid state4 ,illustration3 ,fig4 #bbj4 ,one of the ideas of telegraphic communication4 ,page #bcj ,,chapter ,,xviii4 ,,ruhmkorff',s1 ,,hearder',s1 ,,and ,,bentley',s ,,coil ,,apparatus4 ,in the course of the popular articles on frictional and voltaic electricity1 it has already been mentioned that whilst the intensity effects--such as the capability of the spark to pass through a certain thickness of air1 or the production of the peculiar physiological effect of the shock--belong especially to the phenomena of frictional electricity1 they are not apparent with the quantity effects1 such as may be produced by an ordinary voltaic battery1 unless the latter consists of an immense number of elements1 such as the famous water battery of the late respected ,mr4 ,crosse1 which consisted of two thousand five hundred pairs of copper and zinc cylinders1 well insulated on glass stands1 and protected from dust and light4 ,if1 however1 the feeble intensity current of voltaic electricity1 from four or five elements1 is permitted to pass into a coil of a peculiar construction1 fitted with a condenser1 and manufactured either by ,ruhmkorff of ,paris1 or ,mr4 ,hearder of ,plymouth1 then the most remarkable effects are producible1 which have created quite a new and distinct series of phenomena1 and further established in the most satisfactory manner the connexion between the electricities derived from friction and chemical action4 ,the construction of these coils does not differ very materially1 and great merit is due to ,messrs4 ,ruhmkorff1 ,hearder1 and ,bentley1 who have separately and independently worked out the construction of the most formidable machines of this class4 ,in a letter to the author ,mr4 ,bentley says3-- ,i commence the formation of my coil by using as an axis an iron tube ten inches long and half an inch diameter2 around this is placed a considerable number of insulated iron wires the same length as the tube1 and sufficiently numerous to form a bundle one inch and three quarters diameter4 ,this core is wrapped carefully in eight or nine layers of waxed silk1 the necessity of which will be obvious presently4 ,my primary helix1 which is formed of thirty yards of ,no4 #ad cotton-covered copper wire1 is wound carefully on this core1 and consists of two layers1 each layer being carefully insulated one from the other by waxed silk1 for ,i find that if a wet string or fine platinum wire be connected with the two ends of the primary wires of an induction coil in action1 there is scarcely an indication of an induced current to be obtained from the secondary wire4 ,that this is not owing to any decrease of magnetic power is proved by testing the iron core before and after the experiment1 but is simply owing to the central magnet or coil exerting the whole of its inductive powers upon the nearest closed circuit2 it therefore follows that if the two layers of primary wire are connected by the cotton covering becoming moist1 the whole of the ,page #bca induced current will take this path instead of traversing the secondary wire4 ,before describing my secondary wire ,i must again call attention to the important fact that the magnetism of the iron exerts its inductive power upon the nearest conducting medium2 and ,i have constructed an instrument to demonstrate this fact4 ,it consists simply of an ordinary coil1 giving the third of an inch spark1 but having the four inner layers of secondary wire brought out separately4 ,now1 ,i find that when ,i keep the ends of this wire separate ,i obtain nearly the third of an inch spark1 but when ,i connect them metallically ,i can obtain no intensity spark whatever from the seventeen coils which surround them4 ,it follows from this that before winding the secondary wire the striking distance of a single layer must be ascertained1 and ,i find that with my coil ,i can get a spark one-tenth of an inch long from one coil of wire1 and sufficiently intense to penetrate with facility six layers of waxed silk4 ,waxed silk is therefore unsuited for the insulation of large coils1 and ,i find1 after numerous experiments1 that there is no substance so fitted for the purpose as gutta-percha tissue1 and ,i use five layers of this substance to each layer of wire4 ,the secondary helix then consists of three thousand yards of ,no4 #ce silk-covered copper wire1 and is insulated in the manner described above2 but as ,i do not use cheeks to my coil it assumes the form of a cylinder having rounded ends4 ,for the protection of this instrument ,i place it in a mahogany box of the proper size1 and it is supported and retained in its position by an iron rod1 which is thrust through the hollow axis of the core and the two ends of the box1 leaving half an inch of the iron projecting to work the contact breaker1 which is fixed to one end of the box1 while the two ends of the secondary wire are brought out of the other through gutta percha tubes4 ,the condenser is contained in a separate box1 and is formed of one hundred and twenty sheets of tinfoil between double that number of sheets of varnished paper1 the alternate sides of the foil being brought out and connected to appropriate binding screws4 ,this condenser forms a convenient stand for the coil1 and can be used for many interesting experiments4 ,the shock which the condenser gives to the system depends in a great measure on the size of the coatings4 ,the primary wire alone does not produce any physiological results1 or at least very feeble ones4 ,mr4 ,hearder's coil is wound on a bobbin six inches in length1 and four inches and a half thick1 and includes three thousand yards of covered wire 7,no4 #ce74 ,the iron core consists of a bundle of small wires capped with solid ends1 and the sparks obtained from it were five-eighths of an inch in air when the primary coil was excited by four pairs of ,grove's series2 and when connected with the ,leyden jar1 the most vigorous and brilliant results were produced4 ,the condenser is made of cartridge paper1 coated in the proper manner with tinfoil4 ,the secondary ,page #bcb coil is quite independent of the primary one1 which is laid on in different lengths1 so that the coil can be adjusted to any battery power1 whether for quantity or intensity4 ,for the successful exhibition of the capabilities of the machine1 it is required to perform the experiments in a darkened room4 7,fig4 #bba47 ,illustration3 ,fig4 #bba4 ,ruhmkorff's apparatus4 ,a ,b4 ,the coil1 containing more than a mile of insulated wire4 ,the stand it rests upon1 and with which it is in communication1 contains the condenser4 ,in using this apparatus1 eight pairs of ,grove's battery will be quite sufficient to produce the effects1 and the greatest care must be taken to avoid the shock1 which is most severe and painful1 and might do a great deal of harm to a weakly1 sensitive1 and nervous person4 ,to avoid any accidents of this kind1 the convenient arrangement at one end shown in ,fig4 #bbb must be carefully attended to1 and when manipulating with any part of the apparatus1 if the battery is attached1 the contact should first be broken by bringing the ivory 7the non-conducting7 part of the cylinder ,a 7,fig4 #bbb7 in communication with the conductors1 ,b ,b1 where the wires from the battery are attached4 ,illustration3 ,fig4 #bbb4 ,one end of ,ruhmkorff's coil4 ,b ,b4 ,connexion to receive the battery wires4 ,a is the cylinder1 one half of which is ivory and the other metal4 ,in this position no shock can be received1 because the electricity is cut off by the ivory from the coil4 ,first ,experiment4 ,it is at the other extremity of the coil that the experiments are performed2 for instance1 if an exhausted globe is connected with the pillars ,b ,b 7,fig4 #bbc71 and the connexion made with the battery1 a beautiful faint blue light is apparent on one of the knobs and wires1 and by reversing the current the light appears on the other knob and wire4 ,page #bcc ,this effect is supposed to resemble some of those magnificent streaks and undulations of coloured light called the ,aurora ,borealis2 and1 if the globe is removed from the foot1 and screwed on to the air-pump plate1 and a little alcohol1 ether1 naphtha1 or turpentine placed on wool or tow is held to the air-pump screw1 where the air usually rushes in1 and the cock turned1 so that the vacuum is destroyed1 a quantity of the vapour will necessarily fill the globe2 and if this is once more exhausted1 it presents a different appearance1 being full of coloured light 7varying according to the spirit employed7 but stratified and of a circular form4 7,fig4 #bbc47 ,illustration3 ,fig4 #bbc4 ,end of coil where the experiments are performed4 ,b ,b4 ,connecting screws and wires passing to the exhausted globe1 ,c4 ,the screws are supported on insulating glass pillars1 ,p ,p4 ,second ,experiment4 ,the appearance of these bands of light is modified by the nature of the glass tubes employed1 and the subject has been carefully investigated by ,mr4 ,gassiott4 ,at the last meeting of the ,british ,association at ,aberdeen1 ,dr4 ,robinson made various experiments1 arranged by ,mr4 ,ladd1 for the purpose of showing the connexion between these miniature effects of bands of light in tubes containing various gases1 and the phenomena of the ,aurora ,borealis4 ,the title of the discourse1 which was specially delivered in the ,music ,hall by the learned ,doctor1 was ,on ,electrical ,discharges in ,highly-rarefied ,media1 and it was illustrated by experiments prepared by ,mr4 ,gassiott and ,mr4 ,ladd4 ,the kind of tubes employed may be understood from the next figure4 ,they are made in ,germany1 and by approaching a powerful magnet to ,page #bcd the outside of any of the glass tubes whilst the bands of light are being produced1 the most remarkable modifications of them are obtained4 ,mr4 ,ladd has mounted one of these tubes in a rotatory arrangement similar to that described at page #ahf4 ,when connected with the coil and battery1 it furnishes one of the most lovely electric fire-wheels that can possibly be described4 7,fig4 #bbd47 ,mr4 ,grove placed a piece of carefully-dried phosphorus in a little metallic cup1 and covered it with a jar having a cap and wire4 ,on removing the air from the receiver1 and passing the current of electricity through it from the ,ruhmkorff coil1 he obtained a light completely stratified1 and blended transversely with straight but vibrating dark bands4 ,illustration3 ,fig4 #bbd4 ,a1 ,b1 ,c1 ,d1 ,e1 ,f4 ,various tubes of different kinds of glass1 and containing gases and vapours4 ,each tube has a platinum wire inserted at both ends1 with which the contact is made with the coil4 ,the tube ,a contains mercury1 which has been boiled in it1 and the air expelled4 ,by moving the conducting wire to ,g or ,h1 the light which otherwise passes through the whole of the tubes stops at these points4 ,third ,experiment4 ,when two very thin iron wires are arranged in the upright pillars 7,fig4 #bbc71 and held sufficiently close to each other1 as in ,fig4 #bbe1 light passes from one to the other4 ,the wire from which the light passes remains cold1 the other becomes so hot that it melts into a little globule of liquid iron1 and if paper is held between the wires it rapidly takes fire4 7,fig4 #bbe47 ,illustration3 ,fig4 #bbe4 ,melting of the iron wire4 ,page #bce ,fourth ,experiment4 ,remove the break4 ,attach two wires to ,x ,x 7,fig4 #bbf74 ,hold them so as at pleasure to complete and interrupt the galvanic circle4 ,two other wires are attached at ,p ,p1 their ends being about three-quarters of an inch asunder4 ,when the current is closed or broken at ,a ,a1 a spark passes between ,b ,b4 7,fig4 #bbf47 ,illustration3 ,fig4 #bbf4 ,the making and breaking of the circuit4 ,fifth ,experiment4 ,a ,leyden jar may be charged and discharged with singular rapidity when connected with the coil1 and the snapping noise is so rapid1 that it produces a continuous sharp sound4 7,fig4 #bbg47 ,if a piece of paper is held between the ball of the ,leyden jar and the wire1 it is instantly perforated1 but not set on fire4 ,illustration3 ,fig4 #bbg4 ,a ,b4 ,leyden jar coated with tinfoil1 and standing on any non-conductor1 such as gutta percha or the resinous or glass plate1 ,c4 ,page #bcf ,sixth ,experiment4 ,when the ,leyden jar is coated with spangles of tinfoil1 a spark appears at each break1 and the whole jar is lit up with hundreds of brilliant sparks each time it is charged and discharged1 and as this occurs with amazing rapidity1 the light is almost continuous4 7,no4 #a4 ,fig4 #bbh47 ,the larger the ,leyden jar1 the shorter the spark1 and vice vers4 ,by the employment of a nicely-made screw and inch-scale1 the distance between the discharging points connected with a ,leyden jar can be accurately determined2 and ,mr4 ,hearder states that supposing a ,leyden jar has one square foot of charging surface1 it will give a spark of one inch in length1 but if a smaller jar is used1 with only half a square foot of charging surface1 the spark would be about one inch and a quarter in length4 7,fig4 #bbh47 ,illustration3 ,fig4 #bbh4--,no4 #a4 ,spangled ,leyden jar4 ,no4 #b4 ,hoarder's apparatus for measuring the length of spark for ,leyden jar and coil4 ,p ,p4 ,glass pillars4 ,no4 #c4 ,two best forms of spangles to paste on a ,leyden jar4 ,seventh ,experiment4 ,the direction and rapidity of the current appear to influence greatly the heating and fire-giving power of the coil1 and the following experiment1 devised by ,mr4 ,hearder1 furnishes a curious illustration of this fact4 ,when the current passes in the direction of the arrows 7,fig4 #bbi71 the ,page #bcg platinum wire remains perfectly cool whilst the gunpowder is fired2 and the contrary takes place if the current is reversed--viz41 the gunpowder does not blow up1 but the platinum wire is heated4 ,in the second experiment1 a ,leyden jar is included in the circuit4 7,fig4 #bbi47 ,illustration3 ,fig4 #bbi4 ,a4 ,the coil4 ,b4 ,hearder's discharger1 with thin platinum wire1 ,p1 hanging between the points4 ,c4 ,another discharger1 and powder going off between the points from the little table4 ,the pillars of the dischargers are glass4 ,the arrows show the direction of the current of electricity4 ,eighth ,experiment4 ,amongst so many beautiful experiments1 it is somewhat difficult to say which is the most pleasing1 but for softness and exquisite colouring1 with the continuous vibrating motion of the flowing current of electricity1 nothing can surpass the cascade experiment4 ,this beautiful experiment is usually termed ,gassiott's ,cascade1 and is thus described by that gentleman4 ,two-thirds of a beaker glass1 four inches deep by two inches1 are coated with tinfoil1 leaving one inch and a half of the upper part uncoated4 ,on the plate of an air-pump is placed a glass plate1 and over it the beaker1 covering the whole with an open-mouthed glass receiver1 on which is placed a brass plate having a thick wire passing through a collar of leather2 the portion of the wire within the receiver is covered with a glass tube2 one end of the secondary coil is attached to this wire1 and the other to the plate of the pump4 ,as the vacuum improves the effect is very surprising2 at first a faint clear blue light appears to proceed from the lower part of the beaker to the plate2 this gradually becomes brighter1 until by slow degrees it rises1 increasing in brilliancy until it arrives at that part which is opposite1 or on a line with the inner coating1 the whole being intensely illuminated2 a discharge then commences1 as if the electric fluid were itself a material body running over4 ,this result is obtained by coating the inside of a handsome glass goblet with tinfoil1 and placing it under a jar fitted with a collar of leather and ball1 and arranged in the usual manner on the air-pump4 ,directly a vacuum is obtained1 the ball is moved down to the inside of the goblet1 and the wires from the coil being attached1 a continuous series of streams of ,page #bch electric light seem to overflow the goblet all round the edge1 and it stands then the very embodiment of the brimming cup of fire1 and emblematical of the dangers of the wine-cup4 7,fig4 #bcj47 ,illustration3 ,fig4 #bcj4 ,gassiott's ,cascade4 ,ninth ,experiment4 ,if a piece of wood five inches long and half an inch square is placed on the table of the discharger1 and one wire brought on to the top edge and the other approached to within three inches of it1 and touching the wood1 and the space between them moistened with the strongest nitric acid1 a curious effect is visible from the creeping along of the fire1 which gradually carbonizes and burns the wood4 7,fig4 #bca47 ,illustration3 ,fig4 #bca4 ,burning the piece of wood moistened with the strongest nitric acid4 ,page #bci ,tenth ,experiment4 ,a glass plate wetted with gum1 and then sprinkled with various filings of iron1 zinc1 lead1 copper1 c41 produces a very pretty effect of deflagration as one of the conducting wires is moved over its surface1 the other of course being in contact with the plate4 ,the gum quickly dries by putting the plate in a moderately-heated oven4 ,eleventh ,experiment4 ,when the continuous discharges from the ,leyden jar are made to pass through the centre of a large lump of crystal of alum1 blue vitriol1 or ferroprussiate of potash1 c41 the whole of the crystal is beautifully lighted up during the passage of the electricity from one wire of the discharger to the other4 7,fig4 #bcb47 ,illustration3 ,fig4 #bcb4 ,a4 ,the ,leyden jar4 ,b4 ,large lump of alum1 with a hole bored through it in a line with ,c ,d4 ,the discharging wires are brought within three-eighths of an inch of each other1 and the whole crystal is lighted up with the brilliant electric sparks4 ,twelfth ,experiment4 ,when a piece of paper slightly damped is placed between the wires of the discharger1 the spark is increased to a much greater length1 on account of the conducting power of the water contained in the pores of the paper2 and taking all things into consideration1 the author considers he has witnessed the grandest effects from the coil invented and constructed by ,mr4 ,hearder1 the talented lecturer and electrician of the ,west of ,england4 ,thirteenth ,experiment4 ,electro-magnetic coil machines have been employed for a very considerable time in alleviating certain of the ills which flesh is heir to1 ,page #bdj by the administration of shocks4 ,these may be so regulated as to be hardly perceptible1 or may be so powerful that the pain becomes absolutely intolerable4 ,these coils are now made self-acting1 and consist of two coils of covered and insulated wire wound round a bundle of soft-iron wires1 with the necessary connecting screws for the voltaic battery4 ,the contact with the battery is made and broken with great rapidity by a simple form of break1 consisting of a tinned disc of iron held by a spring over the axis of the bundle of iron wires2 and the continual noise of the break1 which is alternately attracted down to the bundle and brought back by the spring1 when the coil is in contact with the battery1 demonstrates 7without the pain of taking the shock7 when the instrument is in full working order4 ,the coil machine is not only useful in a medical point of view1 but when properly arranged offers a good reception to a run-away bellringer1 and is an excellent preventive against illicit attempts at cheap rides by small boys4 ,illustration3 ,fig4 #bcc4 ,boy1 evidently shocked1 behind doctor's carriage provided with a small coil machine4 ,page #bda ,,chapter ,,xix4 ,,magneto-,,electricity4 ,illustration3 ,fig4 #bcd4 ,clarke's magneto-electrical machine4 ,the correlation of the physical forces1 heat1 light1 electricity1 magnetism1 and motion1 is one of the most interesting subjects for study that can be suggested to the lover of science4 ,the examination of the precise meaning of the term correlation1 so ably considered by ,professor ,grove1 indicates a necessary mutual or reciprocal dependence of one force on the other4 ,thus1 electricity will produce heat1 and vice vers2 motion1 such as friction1 produces electricity1 and the latter1 by its attraction and repulsion1 establishes itself as a source of motion4 ,electricity produces light1 also magnetism1 and contrariwise light is said to possess ,page #bdb the power of magnetizing steel1 whilst magnetism again produces light and electricity4 ,such are the intimate connexions that exist between these imponderable agents1 and we may trace cause and effect and its reversal amongst these forces1 until the mind is lost in the examination of the bewildering mazes1 and is content to return to the beaten track and work out experimentally the practical truths4 ,we have had occasion to notice in another part of this playbook the fact that a current of electricity causes the evolution of magnetism in its passage through various conducting media1 and the truth has been specially illustrated by the various experiments in the chapter devoted to electro-magnetism4 ,in commencing this portion of electrical science1 we have no new terms to coin for the title of the discourse1 as we merely reverse the other when we examine the nature and peculiarities of ,,magneto-,,electricity4 ,the source of the power must necessarily be a bar or horse-shoe shaped piece of steel permanently endowed with magnetism4 ,if the former is thrust into a cylinder of wood or pasteboard1 around which coils of covered copper wire have been carefully wound1 so that the extremities communicate with a galvanometer1 an immediate deflection of the needle occurs1 which1 however1 quickly returns to its first position1 but is again deflected in the opposite direction on the withdrawal of the steel magnet from the coil of copper wire4 7,fig4 #bce47 ,illustration3 ,fig4 #bce4 ,a ,b4 ,coil of copper wire4 ,c4 ,permanent bar magnet placed inside the coil1 when the galvanometer needle1 ,d1 is deflected4 ,the rapid entrance and exit of the steel magnet in the helix of copper wire would be insufficient to produce any quantity of electricity1 and the ingenuity of man has been taxed to arrange a method by which a magnet may be suddenly formed and destroyed inside a coil of insulated copper wire4 ,the difficulty1 however1 has been surmounted by several ingenious contrivances1 based on the principles first discovered by ,faraday2 and the one especially to be noticed is the revolution of a coil of copper wire enclosing a piece of soft iron1 called the armature1 before the poles of a powerful magnet4 ,the first machine was invented ,page #bdc by ,m4 ,hypolyte ,pixii1 of ,paris1 and in #ahcc1 ,mr4 ,saxton improved upon this machine1 and three years afterwards1 ,mr4 ,e4 ,m4 ,clarke described a very ingenious modification of the electro-magnetic machine1 which is depicted at page #bda of this chapter4 ,in this picture1 the letter ,a is the permanent fixed horse-shoe magnets1 which are very appropriately termed the battery magnets1 because they take the position that would otherwise be occupied by a voltaic battery1 and they are indeed the prime source of the electrical power that is evoked4 ,d is the intensity armature which screws into a brass mandril seated between the poles of the magnets ,a1 motion being communicated to it by the multiplying wheel1 ,e4 ,this armature or inductor has two coils of fine insulated copper wire of #aejj yards in length1 coiled on its cylinders1 the commencement of each coil being soldered to the bar ,d1 from which projects a brass stem1 also soldered into ,d1 carrying the break-piece ,h1 which is made fast in any position by a small binding-screw in a hollow brass cylinder to which the other terminations of the coils1 ,f ,f1 are soldered1 these being insulated by a piece of hard wood attached to the brass stem4 ,o is an iron wire spring pressing against one end of the hollow brass cylinder2 ,p is a square brass pillar2 ,q is a metal spring that rubs gently on the break-piece ,h2 ,t is a copper wire for connecting the brass pieces with the wood ,l between them1 and out of which ,p and ,o pass2 ,r ,r are two handles of brass with metallic wires1 the end of one being inserted into either of the brass pieces connected with ,p and ,o1 and the other into the brass stem that carries the break-piece ,h1 delivers a most severe shock directly the wheel is set in motion4 ,in ,saxton's electro-magnetic machine1 the permanent steel magnets are placed horizontally instead of perpendicularly1 and are composed of six or more horse-shoe-shaped pieces of steel4 ,the armatures1 or inductors1 or electro-magnets 7for they consist of pieces of soft round iron with wire wound round them71 are two in number1 and are adapted to exhibit either quantity or intensity effects4 ,the quantity armature is constructed of stout iron1 and covered with thick insulating wire4 ,the intensity armature is made of slighter iron1 and covered with from one thousand to two thousand yards of fine copper wire coated with silk4 ,the quantity armature is intended for the exhibition of results similar to those which are procurable from a voltaic battery1 such as the magnetic spark1 inducing magnetism in soft iron1 heating platinum wire4 ,the intensity armature is employed for the chemical decomposition of water and other bodies1 and likewise for the administration of those terrible blows to the nervous system which cause strong men of the mildest deportment to become painfully excited1 and to make those ejaculations which are so peculiar to the genus ,john ,bull4 ,,experiments ,,with ,,the ,,magneto-,,electric ,,machine4 ,first ,experiment4 ,the decomposition of water by the passage of electricity from one platinum plate to another1 has already been illustrated at page #aih4 ,the ,page #bdd same fact may likewise be displayed by the following arrangement of the machine4 7,fig4 #bcf47 ,illustration3 ,fig4 #bcf4 ,a4 ,apparatus for decomposing water and collecting the gases separately4 ,b ,b4 ,wires proceeding from the machine at ,m1 ,n4 ,q1 works on the single break1 ,h4 ,second ,experiment4 ,the electric light obtained by the passage of the electricity from the battery through the charcoal points1 is also an effect that can be produced by magneto-electric machines1 the wires leading from the points ,a ,b being insulated by glass handles1 and placed in the holes ,m ,n4 7,fig4 #bcg47 ,illustration3 ,fig4 #bcg4 ,the electric light obtained from the magneto machine4 ,page #bde ,third ,experiment4 ,the scintillation of iron wire is one of the most pleasing experiments with this apparatus1 and is performed by pressing gently one end of a piece of thin iron wire 7attached by means of a binding-screw to the upright bar ,a7 against the armature1 ,d4 7,fig4 #bch47 ,illustration3 ,fig4 #bch4 ,deflagration of iron wire4 ,fourth ,experiment4 ,the combustion of ether or other inflammable spirit may also be demonstrated with the aid of this powerful apparatus1 and the arrangement1 in common with the others employed by ,mr4 ,clarke1 is shown in ,fig4 #bci4 ,illustration3 ,fig4 #bci4 ,the break is removed1 and the double blades1 ,b1 fixed in its place4 ,the brass cup1 ,a1 containing mercury is so adjusted that the points will leave the surface of the mercury when the armature is vertical4 ,ether or alcohol poured on the surface is quickly inflamed by the electric spark4 ,with the assistance of the magneto-electric machine1 telegraphic communication may be conducted without the assistance of a battery4 ,it has also been applied to the art of electro-plating by ,mr4 ,j4 ,p4 ,woolrich1 of ,birmingham2 and whilst visiting that place1 the author had the opportunity of witnessing the arrangement employed4 ,it consists of a very powerful magneto-electric machine turned by a steam-engine1 and connected with the large troughs containing the silvering solution4 ,if it is required to deposit a thin coating of silver on the article1 a short period suffices for the action of the machine1 whilst a thick deposit of the precious metal is only obtained by the constant operation of the magnets for several hours4 ,at ,mr4 ,woolrich's factory1 the goods which were being coated with silver were all kept in motion1 moving slowly backwards and forwards in the trough by means of an eccentric connected ,page #bdf with the same steam-engine that worked the electro-magnetic machine4 7,fig4 #bdj47 ,illustration3 ,fig4 #bdj4 ,silvering and plating by the magneto machine1 turned by a steam-engine4 ,the magneto-electric telegraph patented by ,mr4 ,henley in #ahdh1 offers another example of the application of the electric current induced in electro-magnetic coils1 when they rotate in close proximity to the poles of a powerful steel magnet4 ,this telegraph is now in constant use by the ,english and ,irish ,magnetic ,telegraph ,company1 through a distance of more than #bajj miles4 ,the whole length of wires in use amounts to the astonishing quantity of #ac1ijj miles1 of which #fcej miles are hidden underground1 and #gejj conducted above4 ,this telegraph is considered to be one of the simplest and most economical yet brought into practical working4 ,page #bdg ,,chapter ,,xx4 ,,dia-,,magnetism4 ,at the end of the chapter devoted to the subject of light1 will be found an experiment devised and carried out by ,dr4 ,faraday1 in which it is shown that if a bar of a peculiar glass 7called after the inventor1 ,faraday's heavy glass1 or silicated borate of lead7 is subjected to the inductive action of a very powerful electro-magnet1 that it has the power of changing the direction of a ray of polarized light transmitted through it4 ,this effect is not confined to the poles of an electro-magnet1 but is also perceptible 7though in a diminished degree7 with ordinary magnets4 ,the result of this important experiment was communicated to the ,royal ,society by ,dr4 ,faraday on the #bgth ,november1 #ahde1 the enunciation of the fact by this learned philosopher being1 that when 'the line of magnetic force' is made to pass through certain transparent bodies parallel to a ray of polarized light traversing the same body1 the ray of polarized light experiences a rotation4 ,now1 the line of magnetic force means that continual flow of the magnetic current which passes from pole to pole1 and is indicated by iron filings sprinkled on paper placed above the poles of a magnet1 and usually termed magnetic curves1 or the curved lines of magnetic force4 7,fig4 #bda47 ,illustration3 ,fig4 #bda4 ,the curved lines of magnetic force4 ,the heavy glass already alluded to1 upon which the magnet exerts a certain influence1 is called ,,the ,,dia-,,magnetic2 and by this term is meant a body through which the lines of magnetic force are passing without affecting it like iron or steel4 ,at page #bab is a picture representing 7at ,figs4 #bja and #bjb7 the direction of the electricity and that of the magnetic current or whirl at right angles to it4 ,if1 then1 ,fig4 #bjb be considered as a piece of glass1 the arrow ,a ,b ,page #bdh will show the line of magnetic force1 the point ,b being the north pole1 and the shaft ,a the south pole of the magnet1 and the arrows traced round will represent direction4 ,this simple drawing expresses the whole of the law of the action of the magnet on the glass1 and if kept in view1 will give every position and consequence of direction resulting from it4 ,the phenomenon of the affection of the beam of polarized light is immediately connected with the magnetic force1 and this is supposed to be proved by the brightness of the polarized ray being developed gradually1 as the iron coiled with wire requires about two seconds to acquire its greatest power after being connected with the battery4 ,in another experiment of ,faraday's1 where a beam of polarized light was sent through a long glass tube containing water1 and introduced as a core inside a powerful electro-magnetic coil1 the image of a candle viewed with a proper eye-piece1 appeared or disappeared as the battery connexion was made or broken with the coil2 but this result is not considered by many philosophers to be conclusive of the action of magnetism on light1 but rather as an alteration of the refracting power of the medium through which the light passes4 ,these experiments were the precursors of the other effects of magnetism upon different kinds of matter which ,faraday discovered1 and he commenced his examination with a small bar of heavy glass suspended by a filament of silk between the poles of an electro-magnet1 and when the twisting or effects of torsion had ceased1 the battery was connected4 ,directly the current passed1 ,faraday's keen eye detected a movement of the glass1 and on repeating the experiment1 he discovered that the movement was not accidental1 but always took place in a certain fixed direction--viz41 a direction at right angles to a line drawn across and touching the two poles of a horse-shoe-shaped magnet--i4e41 supposing the feeder or bit of soft iron usually placed in contact with the poles of the horse-shoe-magnet to represent the axial line1 any line drawn across it at right angles would be called the equatorial line1 whilst the general space included between the poles of the magnet is called the magnetic field4 ,the movement of the heavy glass was therefore equatorial1 and it pointed east and west instead of north and south1 like iron and steel4 ,illustration3 ,fig4 #bdb4 ,a cube of copper suspended between the poles of a powerful electro-magnet4 ,by the use of the apparatus 7,fig4 #bdb7 ,faraday proved that every ,page #bdi substance1 whether solid1 fluid1 or gaseous1 was subject to magnetic influences1 assuming either the axial or equatorial position4 ,the apparatus consists of a prolongation of the poles of a powerful electro-magnet1 between which the cube of copper1 weighing from a quarter to half a pound1 suspended by a thread1 may be set spinning or rotating4 ,if the electro-magnet is connected with the battery1 the cube stops immediately1 and whilst still in the same position or in the magnetic field1 with the magnet in full action1 it is impossible to set it spinning or twisting round again4 7,fig4 #bdb47 ,a large number of other substances1 solid1 liquid1 and gaseous1 were submitted to the action of the magnet1 the liquids and gases being hermetically sealed in glass tubes1 and some of the results are detailed in the following list3 ,bodies that point axially1 or are paramagnetic1 like a suspended needle4 ,iron4 ,nickel4 ,cobalt4 ,manganese4 ,chromium4 ,cerium4 ,titanium4 ,palladium4 ,platinum4 ,osmium4 ,paper4 ,sealing-wax4 ,fluor spar4 ,peroxide of lead4 ,plumbago4 ,china ink4 ,berlin ,porcelain4 ,red-lead4 ,sulphate of zinc4 ,shell-lac4 ,silkworm-gut4 ,asbestos4 ,vermilion4 ,tourmaline4 ,charcoal4 ,all salts of iron1 when the latter is basic4 ,oxide of titanium4 ,oxide of chromium4 ,chromic acid4 ,salts of manganese4 ,salts of chromium4 ,oxygen1 which stands alone as a paramagnetic gas4 ,bodies that point equatorially1 or are diamagnetic1 like ,faraday's heavy glass4 ,bismuth4 ,antimony4 ,zinc4 ,tin4 ,cadmium4 ,sodium4 ,mercury4 ,lead4 ,silver4 ,copper4 ,gold4 ,arsenic4 ,uranium4 ,rhodium4 ,iridium4 ,tungsten4 ,rock crystal4 ,the mineral acids4 ,alum4 ,glass4 ,litharge4 ,common salt4 ,nitre4 ,phosphorus4 ,sulphur4 ,page #bej ,resin4 ,spermaceti4 ,iceland spar4 ,tartaric acid4 ,citric acid4 ,water4 ,alcohol4 ,ether4 ,sugar4 ,starch4 ,gum-arabic4 ,wood4 ,ivory4 ,dried mutton4 ,fresh beef4 ,dried beef4 ,apple4 ,bread4 ,leather4 ,fresh blood4 ,dried blood4 ,caoutchouc4 ,jet4 ,turpentine4 ,olive oil4 ,hydrogen4 ,carbonic acid4 ,carbonic oxide4 ,nitrous oxide 7moderately74 ,nitric oxide 7very slightly74 ,olefiant gas4 ,coal gas4 ,nitrogen is neither paramagnetic nor diamagnetic1 and is equivalent to a vacuum4 ,magnetically considered1 it is like space itself1 which may be considered as zero4 ,the term magnetic ,faraday proposes should be a general one1 like that of electricity1 and include all the phenomena and effects produced by the power1 and he proposes that bodies magnetic in the sense of iron should be called paramagnetic1 so that the division would stand thus3 ,magnetic 444 ,paramagnetic1 ,diamagnetic2 and it is this division which has been observed in the preceding tables4 99 99 99 99 99 ,all space above and within the limits of our atmosphere may be regarded as traversed by lines of force1 and amongst others are the lines of magnetic force which affect bodies1 as shown in the table of paramagnetic and diamagnetic bodies1 which have the same relation to each other as positive and negative1 or north and south1 in electricity and magnetism4 ,the lines of magnetic force are assumed to traverse void space without change2 but when they come in contact with matter of any kind they are either concentrated upon it or scattered according to the nature of the matter4 ,the power which urges bodies to the axial or equatorial lines is not a central force1 but a force differing in character in the axial or radial directions4 ,if a liquid paramagnetic body were introduced into the field of force1 it would dilate axially1 and form a prolate spheroid like a lemon1 while a liquid diamagnetic body would dilate equatorially1 and form an oblate spheroid like an orange4 ,plcker has demonstrated that if magnetic solutions are placed in watch glasses across the poles of the ,page #bea electro-magnet1 they are heaped up in a very curious manner4 ,the poles of the electro-magnet are pieces of soft iron1 which may be drawn away or approached at pleasure1 and according as the poles are nearer or further asunder1 the magnetic liquids1 such as solution of iron1 are heaped up in one or two directions1 as shown at ,b and ,c in ,fig4 #bdc4 ,illustration3 ,fig4 #bdc4 ,glass dish holding magnetic solution of iron1 and placed in the magnetic field4 ,the diamagnetic power1 doubtless1 says ,faraday1 has its appointed office1 and one which relates to the whole mass of the globe4 ,for though the amount of the power appears to be feeble1 yet1 when it is considered that the crust of the earth is composed of substances of which by far the greater portion belongs to the diamagnetic class1 it must not be too hastily assumed that their effect is entirely overruled by the action of the magnetic matters1 whilst the great mass of waters and the atmosphere must exert their diamagnetic action uncontrolled4 ,plcker has also announced--what at the time he believed to be true--the highly interesting and important fact that the optic axis of ,iceland or calcareous spar is repelled by the magnet and placed equatorially--a fact which ,plcker thought true of many other crystals when the magnetic axis is parallel to the longer crystallographic axis4 ,a piece of kyanite1 which is a mineral composed of sand1 clay1 often lime1 iron1 water1 and is used in ,india1 being cut and polished as a gem1 and sold frequently as an inferior kind of sapphire1 will1 it is said1 even under the influence of the earth's magnetism1 arrange itself like a magnetic needle4 ,plcker believed that he had discovered an existing relation between the forms of the ultimate particles of matter and the magnetic forces1 and he imagined that the results he obtained would lead gradually to the determination of crystalline form by the magnet4 ,the experiments of ,tyndal and ,knoblauch lead1 however1 to a very opposite series of conclusions1 and by ingeniously powdering the crystals with water1 and making them into a paste1 which was afterwards dried and suspended ,page #beb as a model in the magnetic field2 also by taking a slice of apple about as thick as a penny-piece1 with some bits of iron wire through it1 in a direction perpendicular to its flat surface1 they were found to set equatorially not by repulsion but by the attraction of the iron wires2 or instead of the iron by placing bismuth wires1 the apple now settled axially1 not by attraction but by the repulsion of the bismuth4 ,ipecacuanha lozenges1 ,carlisle biscuits also1 suspended in the magnetic field1 exhibited a most striking directive action4 ,the materials in these two cases were diamagnetic2 but owing to the pressure exerted in their formation their largest horizontal dimensions set from pole to pole1 the line of compression being equatorial2 and it is a universal law that in diamagnetic bodies the line along which the density of the mass has been induced by compression sets equatorial1 and in magnetic bodies axial4 ,hence they assume1 from these and many other conclusive experiments1 that crystallized bodies1 such as ,iceland spar1 take their position in the magnetic field without reference to the existence of an optic axis4 ,at the conclusion of a brilliant lecture at the ,royal ,institution by ,dr4 ,tyndal ,on the influence of material aggregation upon the manifestations of force1 in which ,plcker's experiments respecting the repulsion of the optic axis were gracefully discussed and his theory refuted1 the learned doctor said3 ,this evening's discourse is in some measure connected with this locality2 and thinking thus1 ,i am led to inquire wherein the true value of a scientific discovery consists8 ,not in its immediate results alone1 but in the prospect which it opens to intellectual activity--in the hopes which it excites--in the vigour which it awakens4 ,the discovery which led to the results brought before us to-night was of this character4 ,that magnet,e was the physical birthplace of these results2 and if they possess any value they are to be regarded as the returning crumbs of that bread which in #ahdf was cast so liberally upon the waters4 ,i rejoice1 ladies and gentlemen1 in the opportunity here afforded me of offering my tribute to the greatest workman of the age1 and of laying some of the blossoms of that prolific tree which he planted at the feet of the great discoverer of diamagnetism4,f ,footnote ,e3 ,alluding to a splendid magnet made by ,logeman1 which was sent to the ,exhibition in ,hyde-park in #ahea4 ,it could sustain a weight of #dcj pounds1 and was purchased by the ,royal ,institution for ,dr4 ,faraday4 ,footnote ,f3 ,dr4 ,faraday4 ,it was first observed by ,father ,bancalari1 of ,genoa1 that when the flame of a candle is placed between the poles of a magnet it is strongly repelled4 ,the flames of combustible gases from various sources are differently affected1 both by the nature of the combustible and by the nearness of the poles4 ,faraday repeated ,bancalari's experiments1 and by a certain arrangement of the poles of this magnet he obtained a powerful effect in the magnetic field1 and having the axial line of the magnetic force horizontal1 he found that when the flame of a wax taper was held near the axial line 7but on one side or the other71 and about one-third of the flame rising above the level of the upper surface of the ,page #bec poles1 as soon as the magnetic force was exerted the flame receded from the axial line1 moving equatorially until it took an inclined position1 as if a gentle wind was causing its deflection from the upright position4 ,when the flame was placed so as to rise truly across the magnetic axis1 the effect of the magnetism was very curious1 and is shown at ,a1 ,fig4 #bdd4 ,on raising the flame a little more the effect of the magnetic force was to intensify the results already mentioned1 and the flame actually became of a fish-tailed shape1 as at ,c1 ,fig4 #bdd2 and when the flame was raised until about two-thirds of it were above the level of the axial line1 and the poles approached very close1 the flame no longer rose between the poles1 but spread out right and left on each side of the axial line1 producing a double flame with two long tongues1 as at ,b1 ,fig4 #bdd4 ,illustration3 ,fig4 #bdd4 ,effect of magnetism on candle-flame between the poles of the magnet4 ,it was these experiments that led to the important discovery of the paramagnetic property of oxygen1 and proved in a decided manner that gaseous bodies when heated became more highly diamagnetic4 ,oxygen1 which 7tried in the air7 is powerfully magnetic1 becomes diamagnetic when heated4 ,a coil of platinum wire heated by a voltaic current1 and placed beneath the poles of ,faraday's apparatus1 occasioned a strong upward current of air2 but directly the magnetic action commences the ascending current divides1 and a descending current flows down between the upward currents4 ,the discovery1 says ,silliman1 of the highly paramagnetic character of oxygen gas1 and of the neutral character of nitrogen1 the two constituents of air1 is justly esteemed a fact of great importance in studying the phenomena of terrestrial magnetism4 ,we thus see that one-fifth of the air by volume consists of an element of eminent magnetic capacity1 after the manner of iron1 and liable to great physical changes of density1 temperature1 c41 and entirely independent of the solid earth4 ,in this medium hang the magnetic needles used as tests1 and as this magnetic medium is daily heated and cooled by the sun's rays1 its power of ,page #bed transmitting the lines of magnetic force is then affected1 influencing undoubtedly the diurnal changes of the magnetic needle4 ,for a complete digest of ,faraday's discoveries in diamagnetism the reader is referred to the second edition of ,dr4 ,noad's comprehensive and learned work entitled ,a ,manual of ,electricity4 ,coming always from the highest walks of philosophy to lower and common things one cannot help being reminded of the old-fashioned method of drawing up a sluggish fire1 and the natural query is suggested whether the poker is to be considered as a weak magnet1 and does influence and draw towards the fire a greater supply of magnetic oxygen gas8 7,fig4 #bde47 ,illustration3 ,fig4 #bde4 ,illustration3 ,the interior of the optical box at the ,polytechnic--looking towards the screen4 ,the assistants are supposed to be showing the dissolving views4 ,page #bee ,,chapter ,,xxi4 ,,light1 ,,optics1 ,,and ,,optical ,,instruments4 ,illustration3 ,fig4 #bdf4 ,the moon shines bright3--,in such a night as this4--,the ,merchant of ,venice4 ,to gild refined gold1 to paint the lily1 ,to throw a perfume on the violet1 ,to smooth the ice1 or add another hue ,unto the rainbow1 or with taper light ,to seek the beauteous eye of heaven to garnish1 ,is wasteful and ridiculous excess4 ,perfection admits of no addition1 and it is just this feeling that might check the most eloquent speaker or brilliant writer who attempted to offer in appropriate language1 the praises due to that first great creation of the ,almighty1 when the ,spirit of ,god moved upon the face of the waters and said1 ,let there be light4 ,if any poet might be permitted to laud and glorify this transcendant gift1 it should be the inspired ,milton2 who having enjoyed the blessing of light1 and witnessed the varied and beautiful phenomena that accompany it1 could1 when afflicted by blindness1 speak rapturously of its creation1 in those sublime strains beginning with-- ,page #bef ',let there be light1' said ,god1 and forthwith light ,ethereal1 first of things1 quintessence pure1 ,sprung from the deep3 and from her native east ,to journey through the airy gloom began1 ,sphered in a radiant cloud1 for yet the sun ,was not2 she in a cloudy tabernacle ,sojourn'd the while4 ,god saw the light was good1 ,and light from darkness by the hemisphere ,divided3 light the day1 and darkness night1 ,he named4 ,there cannot be a more glorious theme for the poet1 than the vast utility of light1 or a more sublime spectacle1 than the varied and beautiful phenomena that accompany it4 ,ever since the divine command went forth1 has the sun continued to shine1 and to remain1 till time shall be no more1 the great source of light to the world1 to be the means of disclosing to the eye of man all the beautiful and varied hues of the organic and inorganic world4 ,by the help of light we enjoy the prismatic colours of the rainbow1 the lovely and ever changing and ever varied tints of the forest trees1 the flowers1 the birds1 and the insects2 the different forms of the clouds1 the lovely blue sky1 the refreshing green fields2 or even the graceful adornment of the fair1 their beautiful dresses of exquisite patterns and colours4 ,light works insensibly1 and at all seasons1 in promoting marvellous chemical changes1 and is now fairly engaged and used for man's industrial purposes1 in the pleasing art of photography2 just as heat1 electricity1 and magnetism1 7all imponderable and invisible agents17 are employed usefully in other ways4 ,the sources from whence light is derived are six in number4 ,the first is the sun1 overwhelming us with its size1 and destroying life1 sometimes1 with his intense heat and light1 when the piercing rays are not obstructed by the friendly clouds and vapours1 which temper and mitigate their intensity1 and prevent the too frequent recurrence of that quick and dire enemy to man1 the coup de soleil4 ,the body of the sun is supposed to be a habitable globe like our own1 and the heat and light are possibly thrown out from one of the atmospheric strata surrounding it4 ,there are probably three of these strata1 the one believed to envelope the body of the sun1 and to be directly in contact with it1 is called the cloudy stratum2 next to1 and above this1 is the luminous stratum1 and this is supposed to be the source of heat and light2 the third and last envelope is of a transparent gaseous nature4 ,these ideas have originated from astronomers who have carefully watched the sun and discovered the presence of certain black spots called ,macul1 which vary in diameter from a few hundreds of miles to #dj or #ej1jjj miles and upwards4 ,there is also a greyish shade surrounding the black spots called the ,penumbra1 and likewise other spots of a more luminous character termed ,facul2 indeed the whole disc of the sun has a mottled appearance1 and is stippled over with minute shady dots4 ,the cause of this is explained by supposing that these various spots represent openings or breaks in the atmospheric strata1 through which the black body of the sun is apparent or other portions of the three strata1 just as if a black ball was covered with red1 then with yellow1 and finally with blue silk3 on cutting through the blue the yellow is apparent2 by snipping out pieces of the blue and yellow1 the red becomes visible2 and by slicing away a portion of the three silk coverings the black ball at last comes into view4 ,on a similar principle it is ,page #begsupposed that the variety of spots and eruptions on the sun's face or disc may be explained4 ,the evolution of light is not1 however1 confined to the sun1 and it emanates freely from terrestrial matter by mechanical action1 either by friction1 or in some cases by mere percussion4 ,thus the axles of railway carriages soon become red hot by friction if the oil holes are stopped up2 indeed hot axles are very frequent in railway travelling1 and when this happens1 a strong smell of burning oil is apparent1 and flames come out of the axle box4 ,the knife-grinder offers a familiar example of the production of light by the attrition of iron or steel against his dry grindstone4 ,the same result on a much grander scale is produced by the apparatus invented by the late ,jacob ,perkins2 the combustion of steel ensues under the action1 viz41 the friction of a soft iron disc revolving with great velocity against a file or other convenient piece of hardened steel4 7,fig4 #bdg47 ,illustration3 ,fig4 #bdg4 ,instrument for the combustion of steel4 ,the stand has a disc of soft iron fixed upon an axis1 which revolves on two anti-friction wheels of brass4 ,the disc1 by means of a belt worked over a wheel immediately below it1 is made to perform #ejjj revolutions per minute4 ,if the hardest file is pressed against the edge of the revolving disc1 the velocity of the latter produces sufficient heat by the great friction to melt that portion of the file which is brought in contact with it1 whilst some particles of the file are torn away with violence1 and being ,page #beh projected into the air1 burn with that beautiful effect so peculiar to steel4 ,if the experiment is performed in a darkened room1 the periphery of the revolving disc will be observed to have attained a luminous red heat4 ,thirty years ago every house was provided with a tinder-box and matches to strike a light4 ,since the advent of prometheans and lucifers1 the flint and steel1 the tinder1 and the matches dipped in sulphur1 have all disappeared1 and now the box might be deposited in any antiquarian museum under the portrait of ,guy ,fawkes1 and labelled1 an instrument for procuring a light1 extensively used in the early part of the nineteenth century4 7,fig4 #bdh47 ,illustration3 ,fig4 #bdh4 ,c4 ,the steel4 ,b4 ,the flint4 ,e4 ,the tinder4 ,d4 ,the matches of the old-fashioned tinder-box1 ,a4 ,the rubbing of a piece of wood 7hardened by fire1 and cut to a point7 against another and softer kind1 has been used from time immemorial by savage nations to evoke heat and light2 the wood is revolved in the fashion of a drill with unerring dexterity by the hands of the savage1 and being surrounded with light chips1 and gently aided by the breath1 the latent fire is by great and incessant labour at last procured4 ,how favourably the modern lucifers compare with these laborious efforts of barbarous tribes6 a child may now procure a light with a chemically prepared metal1 and great merit is due to that person who first devised a method of mixing together phosphorus and chlorate of potash and so ,page #bei adjusted these dangerous materials that they are as safe as the old tinder-box1 and have now become one of our domestic necessaries4 ,ignition1 or the increase of heat in a solid body1 is another source of light1 and is well illustrated in the production of illuminating power from the combustion of tallow1 oil1 wax1 camphine or coal gas4 ,the term ignition is derived from the ,latin 7ignis1 fire71 and is quite distinct1 and has a totally different meaning from that of combustion4 ,if a glass jar is filled with carbonic acid gas1 and a little tray placed in it containing some gun cotton1 it will be found impossible to fire the latter with a lighted taper1 i4e4 by combustion 7comburo1 to burn71 because the gas extinguishes flame which is dependent on a supply of oxygen2 whereas if a copper or other metallic wire is made red hot or ignited1 the carbonic acid has no effect upon the heat1 and the red hot wire being passed through the gas1 the gun cotton is immediately fired4 ,flame consists of three parts--viz41 of an outer film1 which comes directly in contact with the air1 and has little or no luminosity2 also of a second film1 where carbon is deposited1 and1 first by ignition1 and finally by combustion1 produces the light2 and thirdly1 of an interior space containing unburnt gas1 which is1 as it were1 waiting its turn to reach the external air1 and to be consumed in the ordinary manner4 7,fig4 #bdi47 ,chemical action and electricity have been so frequently mentioned in this work as a source of heat and light1 that it will be unnecessary to do more than to mention them here1 whilst phosphorescence 7the sixth source of light7 in dead and living matter1 a spontaneous production of light1 is well known and exemplified in the glow-worm1 the fire-fly1 the luminosity of the water of the ocean1 or the decomposing remains of certain fish1 and even of human bodies4 ,phosphorescence is still more curiously exemplified by holding a sheet of white paper1 a calcined oyster-shell1 or even the hand1 in the sun's rays1 and then retiring quickly to a darkened room1 when they appear to be luminous1 and visible even after the light has ceased to fall upon them4 ,illustration3 ,fig4 #bdi4 ,a candle flame4 #a4 ,outer flame4 #b4 ,inner flame1 which is badly supplied with oxygen1 and where the carbon is deposited and ignited4 #c4 ,the interior1 containing unburnt gas4 ,for the purpose of examining the temporary phosphorescence of various bodies1 ,m4 ,becquerel has invented a most ingenious instrument1 called the phosphorescope4 ,it ,page #bfj consists of a cylinder of wood one inch in diameter and seven inches long1 placed in the angle of a black box with the electric lamp inside1 so that three-fourths of the cylinder are visible outside1 and the remaining fourth exposed to the interior electric light4 ,by means of proper wheels the cylinder1 covered with any substance 7such as ,becquerel's phosphori71 is made to revolve #cjj times in a second1 and by using this or a lesser velocity1 the various phosphori are first exposed to a powerful light and then brought in view of the spectator outside the box4 ,it is understood that light is produced by an emanation of rays from a luminous body4 ,if a stone is thrown from the hand1 an arrow shot from a bow1 or a ball from a cannon1 we perfectly understand how either of them may be propelled a certain distance1 and why they may travel through space2 but when we hear that light travels from the sun1 which is ninety-five millions of miles away from the earth1 in about seven minutes and a half1 it is interesting to know what is the kind of force that propels the light through that vast distance1 and also what is supposed to be the nature of the light itself4 ,there are two theories by which the nature of light1 and its propagation through space1 are explained2 they are named after the celebrated men who proposed them1 as also from the theoretical mechanism of their respective modes of propulsion3 thus we have the ,newtonian or corpuscular theory of light1 and the ,huyghenian or undulatory theory2 the first named after ,sir ,isaac ,newton1 and the second after ,huyghens1 another most learned mathematician4 ,many years before ,newton made his grand discovery of the composition of light in the year #afgb1 mathematicians were in favour of the undulatory theory1 and it numbered amongst its supporters not only ,huyghens1 but ,descartes1 ,hook1 ,malebranche1 and other learned men4 ,mankind has always been glad to follow renowned leaders1 it is so much easier1 and is in most cases perhaps the better course1 to resign individual opinion when more learned men than ourselves not only adopt but insist upon the truth of their theories2 and this was the case with the corpuscular theory1 which had been written upon systematically and supported by ,empedocles1 a philosopher of ,agrigentum in ,sicily1 who lived some #ddd years before the ,christian era1 and is said to have been most learned and eloquent2 he maintained that light consisted of particles projected from luminous bodies1 and that vision was performed both by the effect of these particles on the eye1 and by means of a visual influence emitted by the eye itself4 ,in course of time1 and at least #bjjj years after this theory was advanced1 philosophers had gradually rejected the corpuscular theory1 until the great ,newton1 about the middle of the seventeenth century1 advanced as a champion to the rescue1 and stamping the hypothesis with his approval1 at once led away the whole army of philosophers in its favour1 so that till about the beginning of the nineteenth century the whole of the phenomena of light were explained upon this hypothesis4 ,the corpuscular theory1 reduced to the briefest definition1 supposes light to be really a material agent1 and requires the student to believe ,page #bfa that this agent consists of particles so inconceivably minute that they could not be weighed1 and of course do not gravitate2 the corpuscles are supposed to be given out bodily 7like sparks of burning steel from a gerb firework7 from the sun1 the fixed stars1 and all luminous bodies2 to travel with enormous velocity1 and therefore to possess the property of inertia2 and to excite the sensation of vision by striking bodily upon the expanded nerve1 the retina1 the quasi-mind of the eye4 ,dr4 ,young remarks1 that according to this projectile theory the force employed in the free emission of light must be about a million million times as great as the force of gravity at the earth's surface1 and it must either act with equal intensity on all the particles of light1 or must impel some of them through a greater space than others1 if its action be more powerful1 since the velocity is the same in all cases--for example1 if the projectile force is weaker with respect to red light than with respect to violet light1 it must continue its action on the red rays to a greater distance than on the violet rays4 ,there is no instance in nature besides of a simple projectile moving with a velocity uniform in all cases1 whatever may be its cause2 and it is extremely difficult to imagine that such an immense force of repulsion can reside in all substances capable of becoming luminous1 so that the light of decaying wood1 or two pebbles rubbed together1 may be projected precisely with the same velocity as the light emitted by iron burning in oxygen gas1 or by the reservoir of liquid fire on the surface of the sun4 ,now one of the most striking circumstances respecting the propagation of light1 is the uniformity of its velocity in the same medium4 ,these and other difficulties in the application of the corpuscular theory aroused the attention of the late ,dr4 ,young1 and in the year #ahja he again revived and supported the neglected undulatory theory with such great ability that the attention of many learned mathematicians was directed to the subject1 and now it may be said that the corpuscular theory is almost1 if not entirely1 rejected1 whilst the undulatory theory is once more1 and deservedly1 used to explain the theory of light1 and its propagation through space4 ,by this hypothesis it is assumed that the whole universe1 including the most minute pores of all matter1 whether solid1 fluid1 or gaseous1 are filled with a highly elastic rare medium of a most attenuated nature1 called ether1 possessing the property of inertia but not of gravitation4 ,this ether is not light1 but light is produced in it by the excitation on the part of luminous bodies of a vibratory motion1 similar to the undulation of water that produces waves1 or the vibration of air affording sound4 ,water set in motion produces waves4 ,air set in motion produces waves of sound4 ,ether1 i4e4 the theoretical ether pervading all matter1 likewise set in motion1 produces light4 ,the nature of a vibratory medium is indeed better understood by reference to that which we know possesses the ordinary properties of matter--viz41 the air2 and by tracing out the analogy between the propagation of sound and light1 the difficulties of the undulatory theory very quickly vanish4 ,to illustrate vibration it is only necessary to procure a finger glass1 and having supported a little ebony ball attached to a silk thread by a bent brass ,page #bfb wire directly over it1 so that the ball may touch either the outside or the inside of the glass1 attention must be directed to the quiescence of the ball when a violin bow is lightly moved over the edge of the glass without producing sound1 and to the contrary effect obtained by so moving and pressing the bow that a sharp sound is emitted1 when immediately the little ball is thrown off from the edge1 the repulsive action being continued as long as the sound is produced by the vibration of the glass4 7,fig4 #bej47 ,illustration3 ,fig4 #bej4 ,a4 ,the finger glass4 ,b4 ,the violin bow4 ,c4 ,the ebony ball4 ,the dotted ball shows how it is repelled during the vibration of the glass4 ,here the vibrations are first set up in the glass1 and being communicated to the surrounding air1 a sound is produced2 if the same experiment could be performed in a vacuum1 the glass might be vibrated1 but not being surrounded with air1 no sound would be produced4 ,this fact is proved by first ringing a bell with proper mechanism fixed under the receiver placed on the air-pump plate2 the sound of the bell is audible until the pump is put in motion and the receiver gradually exhausted1 when the ringing noise becomes fainter and fainter1 until it is perfectly inaudible4 ,this experiment is made more instructive by gradually admitting the air again into the exhausted vessel1 and at the same time ringing the bell1 when the sound becomes gradually louder1 until it attains its full power4 ,the sun and other luminous bodies may be compared to the finger glass1 and are supposed to be endowed naturally with a vibratory motion 7a sort of perpetual ague71 only instead of the air being set in motion1 the ether is supposed to be thrown into waves1 which travel through space1 and convey the impression of light from the luminous object4 ,another familiar example of an undulatory medium is shown by throwing a stone into a pool of water2 the former immediately forces down and displaces a certain number of the particles of the latter1 consequently the surrounding molecules of water are heaped up above their level2 by the force of gravitation they again descend and throw up another wave1 this in subsiding raises another1 until the force of the original and loftier ,page #bfc wave dies away at the edge of the pool into the faintest ripples4 ,it must however be understood that it is not the particles of water first set in motion that travel and spread out in concentric circles2 but the force is propagated by the rising and falling of each separate particle of water as it is disturbed by the momentum of the descending wave before it4 ,when standing at a pier-head1 or on a rock against which the sea dashes1 it is usual to hear the observer cry out1 if the weather is stormy and the waves very high1 ,oh6 here comes a great wave6 as if the water travelled bodily from the spot where it was first noticed1 whereas it is simply the force that travels1 and is exerted finally on the water nearest the rock4 ,it is in fact a progressive action1 just as the wind sweeps over a wide field of corn1 and bends down the ears one after the other1 giving them for the time the appearance of waves4 ,the principle of successive action is well shown by placing a number of billiard balls in a row1 and touching each other2 if the first is struck the motion is communicated through the rest1 which remain immovable1 whilst the last only flies out of its place4 ,the force travels through all the balls1 which simply act as carriers1 their motion is limited1 and the last only changes its position4 ,progressive movement is also well displayed by arranging six or eight magnetized needles on points in a row1 with all their north poles in one direction4 7,fig4 #beb47 ,illustration3 ,fig4 #bea4 ,boy throwing stones into water and producing circular waves4 ,illustration3 ,fig4 #beb4 ,a ,b4 ,series of needles arranged as described4 ,c4 ,the bar magnet1 with the north pole ,n towards the needles4 ,the dotted lines show the direction gradually assumed by all the needles1 commencing at ,d4 ,on approaching the north pole of a bar magnet to the same pole of one ,page #bfd end of the series of needles1 it is very curious to see them turn in the opposite direction progressively1 one after the other1 as the repulsive power of the bar magnet gradually operates upon the similar poles in the magnetic needles4 ,the undulations of the waves of water are also perfectly shown by using the apparatus consisting of the trough with the glass bottom and screen above it1 as described at page #aj4 ,the transmission of vibrations from one place to another is also admirably displayed in ,professor ,wheatstone's ,telephonic ,concert 7see page picture71 where the musical instruments1 as at the ,polytechnic1 were placed by the author in the basement1 and the vibration only conducted by wooden rods to the sounding-boards above1 so that the music was laid on like gas or water4 ,these vibrations or undulations in air1 water1 and the theoretical ether1 have therefore been called waves of water1 waves of sound1 and waves of light1 just as if three clocks were made of three different metals1 the mechanism would remain the same1 though the material1 or in this case the medium1 be different in each4 ,any increase in the number of vibrations of the air produces acute1 whilst a decrease attends the grave sounds1 and when the waves succeed each other not less than sixteen times in a second1 the lowest sound is produced4 ,light and colours are supposed to be due to a similar cause1 and in order to produce the red ray1 no less than #dgg millions of millions of vibrations must occur in a second of time2 the orange1 #ejf2 yellow1 #ece2 green1 #egg2 blue1 #fbb2 indigo1 #feh2 violet1 #fii2 and white light1 which is made up of these colours1 numbers #eda millions of millions of undulations in a second4 ,although light travels with such amazing rapidity1 there is of course a certain time occupied in its passage through space--there is no such thing as instantaneity in nature4 ,a certain period of time1 however small1 must elapse in the performance of any act whatever1 and it has been proved by a careful observation of the time at which the eclipses of the satellites of ,jupiter are perceived1 that light travels at the rate of #aib1ejj miles per second1 and by the aberration of the fixed stars1 #aia1eae1 the mean of these two sets of observations would probably afford the correct rate4 ,such a velocity is1 however1 somewhat difficult to appreciate1 and therefore1 to assist our comprehension of their great magnitude1 ,sir ,j4 ,herschel has given some very interesting comparative calculations1 and coming from such an authority we can readily believe them to be correct4 ,a cannon-ball moving uniformly at its greatest velocity would require seventeen years to reach the sun4 ,light performs the same distance in about seven minutes and a half4 ,the swiftest bird1 at its utmost speed1 would require nearly three weeks to make the tour of the earth1 supposing it could proceed without stopping to take food or rest4 ,light performs the same distance in less time than is required for a single stroke of its wing4 ,dismissing for the present the theory of undulations1 it will be necessary to examine the phenomena of light1 regarding it as radiant matter1 without reference to either of the contending theories4 ,page #bfe ,light issues from the sun1 passes through millions of miles to the earth1 and as it falls upon different substances1 a variety of effects are apparent4 ,there is a certain class of bodies which obstruct the passage of the rays of light1 and where light is not1 a shadow is cast1 and the substance producing the shadow is said to be opaque4 ,wood1 stone1 the metals1 charcoal1 are all examples of opacity2 whilst glass1 talc1 and horn allow a certain number of the rays to travel through their particles1 and are therefore called transparent4 ,nature1 however1 never indulges in sudden extremes1 and as no substance is so opaque as not 7when reduced in thickness7 to allow a certain amount of light to pass through its substance1 so1 on the other hand1 however transparent a body may be1 a greater or lesser number of the rays are always stopped1 and hence opacity and transparency are regarded as two extremes of a long chain2 being connected together by numerous intermediate links1 they pass by insensible gradations the one into the other4 ,if a gold leaf1 which is about the one two-hundredth part of an inch in thickness1 is fixed on a glass plate and held before a light1 a green colour is apparent1 the gold appearing like a green1 semi-transparent substance4 ,when plates of glass are laid one above the other1 and the flame of a candle observed through them1 the light decreases enormously as the number of glass-plates are increased4 ,even in the air a considerable portion of light is intercepted4 ,it has been estimated that of the horizontal sunbeams passing through about two hundred miles of air1 one two-thousandth part only reaches us1 and that no sensible light can penetrate more than seven hundred feet deep into the sea2 consequently1 the vast depths discovered in laying the ,atlantic telegraph must be in absolute darkness4 ,illustration3 ,fig4 #bec4 ,light is thrown out on all sides from a luminous body like the spokes of a cart-wheel1 and in the absence of any obstruction1 the rays are distributed equally on all sides1 diverging like the radii drawn from the centre of a circle4 ,as a natural consequence arising from the divergence of each ray from the other1 the intensity of light decreases as the distance from the luminous source increases1 and vice vers4 ,perhaps the best mechanical notion of this law is afforded by an ordinary fan2 the point from which the sticks radiate1 and where they all meet1 may be ,page #bff termed the light2 the sticks are the rays proceeding from it4 7,fig4 #bec47 ,the fan is held in one hand1 and the first finger of the other can be made to touch all the sticks if placed sufficiently near to ,a2 and supposing the sticks are called rays of light1 the intensity must be great at that point1 because all the rays fall upon it2 but if the finger is removed towards the outer edge--viz41 to ,b1 it now only touches some three or four sticks2 and pursuing the analogy1 a very few rays fall upon that point--hence the light has decreased in intensity1 or to speak correctly1 ,light decreases inversely as the squares of the distance4 ,this law has already been illustrated at page #ac2 and as an experiment1 the rays from the oxy-hydrogen lantern may be permitted to pass out of a square hole 7say two inches square71 and should be thrown on to a transparent screen divided into squares by dark lines1 so that the light at a certain distance illuminates one of them2 then it will be found that at twice the distance1 four may be illuminated1 at three times nine1 and so on4 7,fig4 #bed47 ,illustration3 ,fig4 #bed4 ,lantern at the three distances from the transparent screen1 which is divided into nine equal squares4 ,upon this law is based the use of photometers1 or instruments for measuring light1 and supposing it was required to estimate roughly the illuminating power of any lamp1 as compared with the light of a wax candle six to the pound1 the experiment should be conducted in a dark room1 from which every other light but that from the lamp and candle under examination must be excluded4 ,the lamp1 with the chimney only1 is now placed say twelve feet from the wall1 and a stick or rod is placed upright and about two inches from the latter1 so that a shadow is cast on the wall2 if the candle is now lighted and allowed to burn up properly1 two shadows of the stick will be apparent1 the one from the lamp being black and distinct1 and the other from the candle extremely faint1 until it is approached nearer the ,page #bfg wall--say to within three feet--when the two shadows may be now equal in blackness4 7,fig4 #bee47 ,after this is apparent to one or more persons1 the distances of the lamp and candle from the wall are carefully measured1 and being squared1 and the greater divided by the lesser number1 the quotient gives the illuminating power4 ,for example3 ,the lamp was #ab feet from the wall #ab #ab #add4 ,the candle was #c feet #c #c #i4 #i7 #add ---- #af ,therefore the illuminating power of the lamp is equal to #af wax candles six to the pound4 ,illustration3 ,fig4 #bee4 ,a4 ,the lamp4 ,b4 ,the candle4 ,c4 ,the rod throwing the two shadows1 marked ,d and ,e1 on a white wall or a sheet of paper4 ,there are other and more refined means of working out the same fact1 but for a rough approximation to the truth1 the plan already described will answer very fairly4 ,a most amusing effect can be produced on the principle that every light casts its own shadow1 called the dance of death1 or the dance of the witches2 either of these agreeable subjects are drawn1 and the outlines cut out of a sheet of cardboard4 ,if a wet sheet is stretched or hung on one side of a pair of folding doors partly open1 and between which the cardboard is tacked up1 and the space left at the top and bottom closed with a dark cloth1 directly the room before the sheet is darkened and a lighted candle held behind the figure cut out in the cardboard1 one shadow or image is thrown upon the sheet1 and these shadows may be increased according to the number of candles used1 and if they are held by two or three persons1 and moved up and down1 or sideways1 the shadows follow the direction of the candles1 and present the appearance of a dance4 7,fig4 #bef47 ,page #bfh ,illustration3 ,fig4 #bef4 ,before the curtain4 ,illustration3 ,fig4 #beg4 ,behind the curtain4 ,page #bfi ,another very comic effect of shadow is that called jumping up to the ceiling1 and when carried out on a large scale by the author on an enormous sheet suspended in the centre transept of the ,crystal ,palace1 ,sydenham1 it had a most laughable effect1 and caused the greatest amusement to the children of all ages4 7,fig4 #beh47 ,illustration3 ,fig4 #beh4 ,the laughable effect of the shadows at the ,crystal ,palace4 ,this very telling result is produced by placing an oxy-hydrogen light some feet behind a large sheet1 and of course if any one passes between the two a shadow of the individual is cast upon the sheet1 then by walking towards the light the figure diminishes in size1 and by jumping over it the shadow appears to go up to the ceiling1 and to come down when the jump is made in the opposite direction over the light and towards the sheet4 ,the rationale of this experiment is very simple1 and is ,page #bgj another proof of the distribution of light from a luminous source being in every direction4 ,by jumping over the light the radii projected from the candle over the sheet are crossed1 and the shadow rises or falls as the figure passes upwards or downward4 7,fig4 #bei47 ,illustration3 ,fig4 #bei4 ,the rays of light marked ,a ,b ,c ,d ,e proceeding from a lighted candle or oxy-hydrogen light4 ,the arrow pointing to the right shows how these rays are crossed in jumping up to the ceiling2 and the second arrow1 pointing to the left1 shows the reverse4 ,a beam of light is defined to be a collection of rays1 and it is a convenient definition1 because it prevents confusion to speak only of one ray in attempting to explain how light is disposed of under peculiar circumstances4 ,the smallest portion of light which it is supposed can be separated is therefore called a ray1 and it will pass through any medium of the same density in a perfectly straight line2 but if it passes out of that medium into another of a different density1 or into any other solid1 fluid1 or gaseous matter1 it may be disposed of in four different ways1 being either reflected1 refracted1 polarized1 or absorbed4 ,the reflection of light is the first property that will be considered1 and it will be found that every substance in nature possesses in a greater or lesser degree the power of throwing off the rays of light which fall upon them4 ,thus if we go into a room perfectly darkened1 containing every kind of work produced by nature or art1 such as flowers1 birds1 boxes of insects1 rich carpets1 hangings1 pictures1 statuary1 jewellery1 c41 they cannot excite any pleasure because they are invisible1 but directly a lighted lamp is brought into the chamber1 then the rays fall upon all the surrounding objects1 and being reflected from their surfaces enter the eye1 and there produce the phenomena of vision4 ,this connexion between luminous and non-luminous bodies becomes very apparent when we consider that the sun would appear only as an intense light in a dark background1 if the earth was not surrounded with the various strata of air1 in which are placed clouds and vapours that collectively reflect and scatter the light1 so as to cause it to be endurable to vision4 ,it is when the sky is very clear during ,july or ,august that the heat becomes so intense1 directly clouds begin to form and float about1 the heat is then moderated4 ,many years ago1 ,baron ,alexander ,funk1 visiting some silver mines in ,sweden1 observed1 that in a clear day it was as dark as pitch underground in the eye of the pit at sixty or seventy fathoms deep2 whereas1 on a cloudy or rainy day he could even see to read at #ajf fathoms deep4 ,inquiring of the miners1 he was informed that this is always the case1 and ,page #bga reflecting upon it he imagined very properly that it arose from this circumstance--that when the atmosphere is full of clouds1 light is reflected from them into the pit in all directions1 so that thereby a considerable proportion of the rays are reflected perpendicularly upon the earth2 whereas when the atmosphere is clear there are no opaque bodies to reflect the light in this manner1 at least1 in a sufficient quantity1 and rays from the sun itself can never fall perpendicularly in ,sweden4 ,the use of reflecting surfaces has now become quite common in all crowded cities1 and especially in ,london1 where even the rays of light are too few to be lost1 and flat or corrugated mirrors are placed at various angles1 either to throw the light from the outside on the white-washed ceiling within1 and thus obtain a better diffused light through the apartment1 or it is reflected bodily to some back room1 or rather dark brick box1 where perhaps for half a century candles have been required at an early hour in the afternoon4 ,the brilliant cut in diamonds is such an arrangement of the posterior facets1 or cut faces of the jewel1 that all light reaching them shall be thrown back and reflected1 and thus impart an extraordinary brilliancy to the gem4 ,the intense glare of snow in the ,alpine regions has long been noticed1 and the reflected light is so powerful1 that philosophers were even disposed to believe that snow possessed a natural or inherent luminosity1 and gave out its own light4 ,mr4 ,boyle1 however1 disproved this notion by placing a quantity of snow in a room from which all foreign light was excluded1 and neither he nor his companion could observe that any light was emitted1 although1 on the principle of momentary phosphorescence1 it is quite possible to conceive that if the snow was suddenly brought into a darkened room after exposure to the rays of the sun1 that it would give out for a few seconds a perceptible light4 ,in trying such an experiment1 one person should expose the snow to the sun1 and bring it into a perfectly darkened room to a second person1 whose eyes would be ready to receive the faintest impression of light1 and if any phosphorescence existed1 it must be apparent4 ,the property of reflection is also illustrated on a grand scale in the illumination of our satellite1 the moon1 and the various planetary bodies which shine by light reflected from the sun1 and have no inherent self-luminosity4 ,aristotle was well aware that it is the reflection of light from the atmosphere which prevents total darkness after the sun sets1 and in places where the sun's rays do not actually fall during the daytime4 ,he was also of opinion that rainbows1 halos1 and mock suns1 were all occasioned by the reflection of the sunbeams in different circumstances1 by which an imperfect image of the sun was produced1 the colour only being exhibited1 but not the proper figure4 ,the image1 ,aristotle says1 is not single1 as in a mirror1 for each drop of rain is too small to reflect a visible image1 but the conjunction of all the images is visible4 ,aristotle ascribed all these effects to the reflection of light1 and it will be noticed when we come to the consideration of the refraction of light1 that of course his views must be seriously modified4 ,page #bgb ,the reflection of light is affected rather by the condition of the surface than the whole body of a substance1 as a piece of coal may be covered with gold or silver leaf and caused to shine1 whilst the brightest mirror is dimmed by the thinnest film of moisture4 ,from whatever surface light is reflected1 it always takes place in obedience to two fixed laws4 ,first4 ,the incident and reflected rays always lie in the same plane4 ,second4 ,the angle of incidence is equal to the angle of reflection4 ,with a single jointed two-foot rule1 both of these laws are easily illustrated4 ,the rule may be held in the hand1 and one end being marked with a piece of white paper may be called the incident ray1 i4e41 the ray that falls upon the surface2 and the other is the reflected ray1 the one cast off or thrown back4 ,a perpendicular is raised by holding a stick upright at the joint4 7,fig4 #bfj47 ,illustration3 ,fig4 #bfj4 ,a ,d4 ,a two foot rule2 the end ,a may be termed the incident ray1 and the end ,d the reflected ray4 ,s4 ,the stick held perpendicularly4 ,the angle ,a ,b ,c is equal to the angle ,d ,e ,f1 and the whole may be moved in any direction or plane1 either horizontal or perpendicular1 ,g ,g4 ,the reflecting surface4 ,one of the most simple and pleasing delusions produced by the reflection of light1 is that afforded by cutting through the outline of a vase1 or statuette1 or flower1 drawn on cardboard1 and if certain points are left attached1 so that the design may not fall out1 all the effect of solidity is given by bending back the edges of the cardboard1 so that the light ,page #bgc from a candle placed behind it1 may be reflected from the back edge of one cardboard on to the design1 which is bent back4 ,the light reflected from one surface on to the other1 imparts a peculiarly soft and marble-like appearance1 and when the design is well drawn and cut1 and placed in a good position1 the illusion is very perfect1 and it appears like a solid form instead of a mere design cut out of cardboard4 7,fig4 #bfa47 ,illustration3 ,fig4 #bfa4 ,cardboard design in frame1 cut and bent back4 ,the lighted candle is behind4 ,the leaf at the side of the above picture is intended to give an idea of the mode of cutting out the designs1 and in this case the leaf would be cut and bent back1 and a small attachment slip of cardboard left to prevent it falling out4 ,the cardboard design is always bent toward the light1 which is placed behind it4 ,as a good illustration of the importance of reflected light and its connexion with luminous bodies1 a beam of light from the oxy-hydrogen lantern may be allowed to pass above the surface of a table1 when it will be noticed that the latter is lighted up only when the beam is reflected downward by a sheet of white paper4 ,by reference to the two laws of reflection already explained1 it is easy to trace out on paper1 with the help of compasses and rule1 the effect of plane1 concave1 and convex surfaces on parallel1 diverging1 or converging rays of light1 and it may perhaps assist the memory if it is remembered that a plane surface means one that is flat on both sides1 such as a looking-glass3 a convex surface is represented by the outside of a watch-glass2 a concave surface1 by the inside of a watch-glass2 parallel ,page #bgd rays are like the straight lines in a copy-book2 diverging and converging rays1 are like the sticks of a fan spread out as the sticks separate or diverge2 the sticks of the fan come together1 or converge at the handle4 ,the reflection of rays from a plane surface may be better understood by reference to the annexed diagram4 7,fig4 #bfb47 ,illustration3 ,fig4 #bfb4 ,a ,i1 ,a ,k4 ,two diverging rays incident on the plane surface1 ,d4 ,a ,d is perpendicular1 and is reflected back in the same direction4 ,a ,i is divergent1 and is thrown off at ,i ,l4 ,the incident and reflected rays forming equal angles1 as proved by the perpendicular1 ,h4 ,any image reflected in a plane mirror appears as far behind it as the object is before it1 and the dotted lines meeting at ,g show the apparent position of the reflected image behind the glass1 as seen at ,g4 ,the same fact is also shown in the second diagram1 where the reflected picture1 ,i ,m1 appears at the same distance behind the surface of the mirror as the object1 ,a ,b1 is before it4 ,by the proper arrangement of plane mirrors1 a number of amusing delusions may be produced1 one of which is sometimes to be met with in the streets1 and is called the art of looking through a four-inch deal board4 ,the spectator is first requested to look into a tube1 through which he sees whatever may be passing the instrument at the time2 the operator then places a deal board across the middle of the tube1 which is cut away for that purpose1 and to the astonishment of the juveniles the view is not impaired1 and the spectator still fancies he is looking through a straight tube2 this however is not the case1 as the deception is entirely carried out by reflection1 and is explained in the next cut4 7,fig4 #bfc47 ,page #bge ,illustration3 ,fig4 #bfc4 ,a ,a ,a ,a4 ,the apertures through which the spectator first looks4 ,b4 ,the piece of wood1 four inches thick4 ,c1 ,d1 ,e1 ,f1 are four pieces of looking-glass1 so placed that rays of light entering at one end of the tube are reflected round to the other where the eye of the observer is placed4 ,during the siege of ,sebastopol numbers of our best artillerymen were continually picked off by the enemy's rifles1 as well as by cannon shot1 and in order to put a stop to the foolhardiness and incautiousness of the men1 a very ingenious contrivance was invented by the ,rev4 ,wm4 ,taylor1 the coadjutor of ,mr4 ,denison in constructing the first ,big ,ben bell4 ,it was called the reflecting spy-glass1 and by its simple construction rendered the exposure of the sailors and soldiers1 who would look over the parapet or other parts of the works to observe the effect of their shot1 perfectly unnecessary2 whilst another form was constructed for the purpose of allowing the gunner to lay or aim his gun in safety4 ,the instruments were shown to ,lord ,panmure1 who was so convinced of the importance of the invention1 that he immediately commissioned the ,rev4 ,wm4 ,taylor to have a number of these telescopes constructed2 and if the siege had not terminated just at the time the invention was to have been used1 no doubt a great saving of the valuable lives of the skilled artillerymen would have been effected in the allied armies4 ,the principle of the reflecting spy-glass may be comprehended by reference to the next cut4 7,fig4 #bfd47 ,illustration3 ,fig4 #bfd4 ,a picture of enemy's battery is supposed to be on the mirror1 ,a1 whence it is reflected to ,b1 and from that to the artilleryman at ,c4 ,by placing two mirrors at an angle of #de1 the reflected image of a person gazing into one is thrown into the other1 and of course the effect is somewhat startling when a death's head and cross bones1 or other ,page #bgf cheerful subject1 is introduced opposite one mirror1 whilst some person who is unacquainted with the delusion is looking into the other4 ,two adjoining rooms might have their looking-glasses arranged in that manner1 provided there is a passage running behind them4 7,fig4 #bfe47 ,illustration3 ,fig4 #bfe4 ,a4 ,a mirror at an angle of #de degrees4 ,the arrows show the direction of the reflected image4 ,b4 ,the second mirror1 also at an angle of #de degrees2 the face of the person looking in at ,a is reflected at ,b4 ,c is the partition between the rooms4 ,one of the most startling effects that can be displayed to persons ignorant of the common laws of the reflection of light1 is called the magic mirror1 and is described by ,sir ,walter ,scott in his graphic story of that name4 ,the apparatus for the purpose must be well planned and fixed in a proper room for that purpose1 and if carefully conducted1 may surprise even the learned4 ,a long and somewhat narrow room should be hung with black cloth1 and at one end may be placed a large mirror1 so arranged that it will turn on hinges like a door4 ,the magician's circle may be placed at the other end of the chamber in which the spectators must be rigidly confined1 and there is very little doubt that the arrangement about to be described was formerly used by clever astrologers who pretended to look into the future1 and to hold communication with the supernatural powers4 ,the credulity of the persons who consulted these wise men1 is not surprising when we consider the ignorance of the public generally of common physical laws1 and of the wonders that may be worked without the assistance of the evil one2 moreover1 the initiated took great care to conceal the machinery of their mysteries1 never imparting the illusive tricks even to their most faithful dependents except under solemn oaths of secrecy1 because they derived in many cases considerable profit by their pretended conjurations and juggling tricks1 and therefore were interested in keeping the outer world in ignorance4 ,the wizards were always careful to impress those who came to consult them with the awful nature of the incantations they were about to perform1 and with such a powerful auxiliary as ,page #bgg fear1 and a well-darkened room1 they diverted the thoughts of the more curious1 and prevented them watching the proceedings too closely4 ,theatrical effects were not disdained1 such as suppressed and dismal groans1 sham thunder1 and the wizard usually heightened his own inspiring personal appearance by wearing of course a long beard and flowing robe trimmed with hieroglyphics1 and with the assistance of a ponderous volume full of cabalistic signs1 a few skulls and cross bones1 an hour-glass1 a pair of drawn swords1 a black cat1 a charcoal fire1 and sundry drugs to throw into it1 a very tolerable collection of imps1 familiars1 and demons1 might be expected to attend without the modern practice of spirit-rapping4 ,as before stated1 the delusion must be carefully conducted1 and a confederate is necessary in order to use the phantasmagoria1 or magic lantern4 ,the slides of course were painted to suit the fortune to be unfolded--an easy road to riches for the gentlemen1 a tale of love1 ending in matrimony1 for the ladies4 ,the spectators being placed in the magic circle1 are directed to look into the mirror2 they may even be ordered singly to fetch a skull off the mantel-shelf beside the mirror1 and whilst doing so to look full into the mirror1 and then return to the circle4 ,absolute silence is enjoined1 and soft music is now heard2 the darkened room is lit up for the moment by a little yellow or green fire thrown on to the charcoal fire1 and now looking into the mirror1 it no longer reflects surrounding objects1 but a picture1 at first small and faint1 and then gradually becoming large and clearer1 is apparent4 ,the picture is made visible by the confederate gently drawing the mirror from its position parallel with the frame to an angle of #de degrees1 and then throwing on from the side a picture from a magic-lantern4 ,the picture is small and indistinct whilst the confederate holds it near the mirror and out of focus1 but as he moves backwards and focuses the lenses1 the picture gradually increases in size1 and the reflecting angles having been well planned beforehand1 only those in the circle will be able to see the picture1 and great fun may be elicited from the magic mirror by pretending to tell the future fate of a very slim person1 and introducing him by a succession of pictures which gradually assume a ,john ,bull rotundity of figure1 surrounded by dozens of children2 whilst to young ladies who are engaged1 a provoking picture of an old maid may be introduced2 indeed1 there is no end to the innocent fun that may be extracted from the magic mirror1 and the whole plan of the delusion may be better understood by reference to the next picture4 7,fig4 #bff47 ,monsieur ,salverte very properly remarks that man is credulous from his cradle to his tomb2 but the disposition springs from an honourable principle1 the consequences of which precipitate him into many errors and misfortunes4444 ,the novelty of objects1 and the difficulty of referring them to known objects1 will not shock the credulity of unsophisticated men4 ,there are some additional sensations which he receives without discussion1 and their singularity is perhaps a charm which causes him to receive them with greater pleasure4 ,man almost always loves and seeks the marvellous4 ,is this taste natural8 ,page #bgh ,illustration3 ,the magic mirror4 ,illustration3 ,fig4 #bff4 ,plan of room4 ,a ,a4 ,the frame of the looking-glass4 ,a ,b4 ,mirror put back to an angle of #de degrees4 ,c4 ,the confederate who manages the lantern and shuts the glass to the frame after each fortune is told4 ,d4 ,the magic circle1 to which the rays are reflected4 ,page #bgi ,does it spring from the education which during many ages the human race has received from its first instructors8 ,a vast and novel question1 but with which ,i have nothing to do4 ,it is sufficient to observe that as the lover of the wonderful always prefers the most surprising to the most natural account1 this last has been too frequently neglected1 and is irrevocably lost4 ,occasionally1 however 7and we shall cite more than one instance71 simple truth has escaped from the power of oblivion4 ,credulous man may be deceived once1 or more frequently2 but his credulity is not a sufficient instrument to govern his whole existence4 ,the wonderful excites only a transient admiration4 ,in #agih1 the ,french savans remarked with surprise how little the spectacle of balloons affected the indolent ,egyptian4444 ,but man is led by his passions1 and particularly by hope and fear4 ,when parallel rays fall upon a convex mirror1 they are scattered and dispersed in all directions1 and the image of an object reflected in a convex mirror appears to be very small1 being reduced in size because the reflected picture ,i ,m is nearer the surface of the mirror than the object ,a ,b4 ,no4 #a4 7,fig4 #bfg47 ,illustration3 ,fig4 #bfg4 ,a ,b1 ,d ,h4 7,no4 #b7 represent two parallel rays incident on the convex surface ,b ,h1 the one 7,a ,b7 perpendicularly1 the other 7,d ,h7 obliquely4 ,c is the centre of convexity4 ,h ,e is the reflected ray of the oblique incident one1 ,d ,h2 whilst ,c ,h ,i is the perpendicular4 ,convex mirrors are not employed in any optical deception on a large scale1 although some ingenious delusions are producible from cylindrical and conical mirrors1 and are thus described by ,sir ,david ,brewster3 ,among the ingenious and beautiful deceptions of the seventeenth century1 we must enumerate that of the re-formation of distorted pictures by reflection from cylindrical and conical mirrors4 ,in these representations1 the original image from which a perfect picture is produced1 ,page #bhj is often so completely distorted1 that the eye cannot trace in it the resemblance to any regular figure1 and the greatest degree of wonder is of course excited1 whether the original image is concealed or exposed to view4 ,these distorted pictures may be drawn by strict geometrical rules1 and ,i have shown a simple method of executing them4 ,let ,m be an accurate cylinder made of tin-plate or of thick pasteboard4 ,out of the further side of it cut a small aperture1 a b c d1 and out of the nearer side cut a larger one1 ,a ,b ,c ,d 7white letters71 the size of the picture to be distorted2 having perforated the outline of the picture with small holes1 place it in the opening ,a ,b ,c ,d 7white letters71 so that its surface may be cylindrical2 let a candle or a bright luminous object--the smaller the better--be placed at ,s1 as far behind the picture ,a ,b ,c ,d 7white letters7 as the eye is afterwards to be placed before it1 and the light passing through the small holes will represent on a horizontal plane a distorted image of the picture at ,a ,b ,c ,d1 which1 when sketched in outline with a pencil1 shaded1 and coloured1 will be ready for use4 ,if we now substitute a polished cylindrical mirror of the same size in place of ,m1 then the distorted picture1 when laid horizontally at ,a ,b ,c ,d1 will be restored to its original state when seen by reflection at ,a ,b ,c ,d 7white letters7 in the polished mirror4 ,the effect of a cylindrical mirror on a distorted picture is shown at ,no4 #b1 being copied from an old one seen by ,sir ,d4 ,brewster4 ,illustration3 ,fig4 #bfh4 ,by looking at a reflection of the face in a dish-cover or the common surface of a bright silver spoon or of a silver mug1 the latter truly becomes ugly as the image is seen reflected from its surface1 and ,page #bha assumes the most absurd form as the mouth is opened or shut1 and the face advanced or removed from the silver vessel4 7,fig4 #bfi47 ,illustration3 ,fig4 #bfi4 ,distorted image produced by an irregular convex surface4 ,in the writings of the ancients there are to be found certain indications of the results of illusions produced by simple optical arrangements1 and the sudden and momentary apparition 7from the gloom of perfect darkness7 of splendid palaces1 delightful gardens1 c41 with which-the concurrent voice of antiquity assures us-the eyes of the beholders were frequently dazzled in the mysteries1 such as the evocation and actual appearance of departed spirits1 the occasional images of their umbr1 and of the gods themselves4 ,from a passage in ,pausanias1 7,boeotic ,,xxx471 when1 speaking of ,orpheus1 he says there was anciently at ,aornos1 a place where the dead were evoked1 ,greek3 nekuomanteion1 we learn that in those remote ages there were places set apart for the evocation of the dead4 ,homer relates1 in the eleventh book of the ,odyssey1 the admission of ,ulysses alone into a place of this kind1 when his interview with his departed friend was interrupted by some fearful voice1 and the hero1 apprehending the wrath of ,proserpine1 withdrew2 the priests who managed these deceptive exhibitions no doubt adopted this method of getting rid of their visitor1 who might become too inquisitive1 and discover the secret of the mysteries4 ,of all the reflecting surfaces mentioned1 none produce more interesting deceptions than the concave mirror1 and there is very little doubt that silver mirrors of this form were known to the ancients1 and employed in ,page #bhb some of their sacred mysteries4 ,mons4 ,salverte has industriously collected in his valuable work the most interesting proofs of their use1 and quotes the following passage of ,damascius1 in which the results obtainable from a concave mirror are clearly apparent4 7,fig4 #bgj47 ,illustration3 ,fig4 #bgj4 ,the picture of a human face1 possibly reflected from a concave mirror concealed below the floor of the temple2 the opening being hidden by a raised mass of stone1 and the worshippers confined to a certain part of the temple1 and not allowed to approach it4 ,he says3--,in a manifestation which ought not to be revealed 444 there appeared on the wall of the temple a mass of light which at first seemed very remote2 it transformed itself in coming nearer into a face evidently divine and supernatural1 of a severe aspect1 but mixed with gentleness1 and extremely beautiful4 ,according to the institution of a mysterious religion1 the ,alexandrians honoured it as ,osiris and ,adonis4 ,parallel rays thrown upon a concave surface are brought to a focus or converge1 and when an object is seen by reflection from a concave surface1 the representation of it is various1 both with regard to its ,page #bhc magnitude and situation1 according as the distance of the object from the reflecting surface is greater or less4 7,fig4 #bga47 ,when the object is placed between the focus of parallel rays and the centre1 the image falls on the opposite side of the centre1 and is larger than the object1 and in an inverted position4 ,the rays which proceed from any remote terrestrial object are nearly parallel at the concave mirror--not strictly so1 but come diverging to it in separate pencils1 or1 as it were1 bundles of rays1 from each point of the side of the object next the mirror2 therefore they will not be converged to a point at the distance of half the radius of the mirror's concavity from its reflecting surface1 but in separate points at a little greater distance from the concave mirror4 ,the nearer the object is to the mirror1 the further these points will be from it1 and an inverted image of the object will be formed in them1 which will seem to hang pendant in the air1 and will be seen by an eye placed beyond it 7with regard to the mirror71 in all respects like the object1 and as distinct as the object itself4 ,no4 #b4 7,fig4 #bga47 ,illustration3 ,fig4 #bga4 ,no4 #a4 ,a ,b1 ,d ,h represent two parallel rays incident on the concave surface ,b ,h1 whose centre of concavity is ,c4 ,b ,f and ,h ,f are the reflected rays meeting each other in ,f1 and ,a ,b being perpendicular to the concave surface1 is reflected in a straight line4 ,no4 #b4 ,a ,b4 ,the object4 ,i ,m4 ,the image4 ,illustration3 ,fig4 #bgb4 ,a ,b represents the object1 ,s ,v the reflecting surface1 ,f its focus of parallel rays1 and ,c its centre4 ,through ,a and ,b1 the extremities of the object1 draw the lines ,c ,e and ,c ,n1 which are perpendicular to the surface1 and let ,a ,r1 ,a ,g1 be a pencil of rays flowing from ,a4 ,these rays proceeding from a point beyond the focus of parallel rays1 will1 after reflection1 converge towards some point on the opposite side of the centre1 which will fall upon the perpendicular1 ,b ,c1 produced1 but at a greater distance from ,c than the radiant ,a from which they diverged4 ,for the same reason1 rays flowing from ,b will converge to a point in the perpendicular ,n ,c produced1 which shall be further from ,c than the radiant ,b1 from whence it is evident that the image ,i ,m is larger than the object ,a ,b1 that it falls on the contrary side of the centre1 and that their positions are inverted with respect to each other4 ,page #bhd ,it appears1 from a circumstance in the life of ,socrates1 that the effects of burning-glasses were known to the ancients2 and it is probable that the ,romans employed the concave speculum for the purpose of lighting the sacred fire4 ,this is very likely to be true1 considering that the priests who conducted the heathen worship of ,osiris and ,adonis were acquainted with the use of concave metallic specula1 as already described at page #bhb4 ,the effects that can be produced with the aid of concave mirrors are very impressive1 because they are not merely confined to the reflection of inanimate objects1 but life and motion can be well displayed by them2 thus1 if a man place himself directly before a concave mirror1 but further from it than its centre of concavity1 he will see an inverted image of himself in the air between him and the mirror of a less size than himself2 and if he hold out his hand towards the mirror the hand of the image will come out towards his hand and coincide with it1 being of an equal bulk when his hand is in the centre of concavity1 and he will imagine he may shake hands with his image4 7,fig4 #bgc47 ,illustration3 ,fig4 #bgc4 ,a concave mirror1 showing the appearance of the inverted and reflected image in the air4 ,by using a large concave mirror of about three feet in diameter1 the author was enabled to show all the results to a large audience that were usually visible to one person only4 ,whilst experimenting with a concave mirror1 by holding out the hand in the manner described1 a bystander will see nothing of the image1 because none of the reflected rays that form it enter his eyes4 ,this circumstance is well illustrated by placing a concave mirror opposite the fire1 and allowing the image of the flames projected from it to fall upon a well-polished mahogany table4 ,if the door of the room opens towards the mirror1 and a spectator unacquainted with the properties of concave mirrors should enter the apartment1 the person would be greatly startled to see flames apparently playing over the surface of the table1 whilst another spectator might enter from another door and see nothing but a long beam of light1 rendered visible by the floating particles of dust4 ,to give proper effect to this experiment the concave mirror should be large1 and no other light must illuminate the room except that from the fire4 ,on the same polished table the appearance of a planet with a revolving ,page #bhe satellite may be prettily shown by darkening the fire with a screen1 and placing a lighted candle before it1 which will be reflected by the concave mirror1 and appear on the table as a brilliant star of light1 and the satellite may be represented by the flame of a small wax taper moved around the large burning candle4 ,the following is the arrangement used by the author at the ,polytechnic ,institution for the purpose of exhibiting the properties of the concave mirror4 ,a lantern enclosing a very brilliant light1 such as the electric or lime light1 is required for the illumination of the objects which are to be projected on to the screen4 ,the lantern and electric lamp of ,duboscq was preferred1 although1 of course1 any bright light enclosed in a box1 with a plain convex lens to project the beam of light when required1 will answer the purpose4 7,fig4 #bgd47 ,illustration3 ,fig4 #bgd4 ,a ,b4 ,portable screen of light framework1 covered with black calico4 ,c ,c ,c ,c4 ,square aperture just above the shelf1 ,d ,d1 upon which the object--viz41 a bottle half full of water--is placed4 ,e4 ,duboscq lantern to illuminate the object at ,d ,d4 ,by removing the diaphragm required to project the picture of the charcoal points on to the screen1 a very intense beam of light is obtained1 which may be focussed or concentrated on any opaque object by another double convex lens1 conveniently mounted with a telescope stand1 so that it may be raised or lowered at pleasure4 ,this lens is independent of the lantern1 and may be used or not at the pleasure of the operator4 ,the object is now placed on a shelf fixed to the screen1 with a square aperture just above it4 ,the object of the screen is to cut off all extraneous rays of light reflected from the mirror1 or to increase the sharpness of the outline of the picture of the object4 ,the screen and object being arranged1 and the light thrown on from the lantern1 the next step is to adjust the concave mirror1 and by moving it towards the ,page #bhf object1 or backwards1 as the case requires1 a good image1 solid and quasi-stereoscopic1 is projected on to the screen4 7,fig4 #bge47 ,illustration3 ,fig4 #bge4 ,a4 ,the concave mirror4 ,b4 ,the lantern4 ,c4 ,the portable screen1 shelf1 and object4 ,d4 ,the inverted image of the bottle filling with water1 with the neck downwards1 and when thrown on the disc at ,d producing a most curious illusion4 ,the act of filling the bottle with water1 or better still with mercury1 is one of the most singular effects that can be shown2 and if all the apparatus is enclosed in a box1 so that the picture on the screen only is apparent1 the illusion of a bottle being filled in an inverted position is quite magical1 and invariably provokes the inquiry1 how can it be done8 ,the study of numismatics1 the science of coins and medals1 is generally considered to be limited to the taste of a very few persons1 and any description of a collection of coins at a lecture would be voted a great bore1 unless1 of course1 the members of the audience happened to be antiquaries2 great light1 however1 may be thrown on history by a study of these interesting remains of bygone times1 and a lecture on this subject1 illustrated with pictures of coins thrown on to the disc by a concave mirror in the manner described1 might be made very pleasing and instructive4 ,coins1 or plaster casts of coins gilt1 flowers1 birds1 white mice1 the human face and hands1 may all1 when fully illuminated1 be reflected by the concave mirror on to the disc4 ,a ,daguerreotype picture at a certain angle appears1 when reflected by the concave mirror1 to be like any ordinary collodion negative1 and all the lights and shadows are reversed1 so that the face of the portrait appears black1 whilst the black coat is white4 ,on placing the ,daguerreotype in another position1 easily found by experiment1 it is now reflected in the ordinary manner1 showing an enlarged and perfect portrait on the disc4 ,in using the ,daguerreotype the glass in front of it must be removed4 ,the pictures from the concave mirror may be also projected on thick smoke procured from ,page #bhg smouldering damped brown paper1 or from a mixture of pitch and a little chlorate of potash laid on paper1 and allowed to burn slowly by wetting it with water4 ,an image reflected from smoke would be visible to a number of spectators1 just as the light from the furnace fires of the locomotive is frequently visible at night1 being reflected on the escaping column of steam4 ,it was probably with the help of some kind of smoke and the concave speculum that the deception practised on the worshippers at the temple of ,hercules at ,tyre was carried out1 as it is mentioned by ,pliny that a consecrated stone existed there from which the gods easily rose4 ,at the temple of ,esculapius at ,tarsus1 and that of ,enguinum in ,sicily1 the same kind of optical delusions were exhibited as a portion of the religious ceremonies1 from which no doubt the priests obtained a very handsome revenue1 much more than could be obtained in modern times by the mere exhibition of such wonders at ,adelaide ,galleries1 ,polytechnics1 or ,panopticons4 ,the smoke from brown paper is very useful in showing the various directions of the rays of light when reflected from plane1 convex1 and concave surfaces4 ,the equal angles of the incident and reflected rays may be perfectly shown by using the next arrangement of apparatus4 7,fig4 #bgf47 ,illustration3 ,fig4 #bgf4 ,a4 ,rays of light slightly divergent issuing from the lantern1 and received on a little concave mirror1 which brings the rays almost parallel1 and reflects them to ,e1 a piece of looking-glass1 from which they are again reflected4 ,c is the incident1 and ,d the reflected rays4 ,f4 ,smoke from brown paper4 ,a very dense white smoke is obtained by boiling in separate flasks 7the necks of which are brought close together7 solutions of ammonia and hydrochloric acid4 ,the opposite properties of convex and concave mirrors--the former scattering and the latter collecting the rays of light which fall upon them--are also effectively demonstrated by the help of the same illuminating ,page #bhh source and proper mirrors1 the smoke tracing out perfectly the direction of the rays of light4 7,fig4 #bgg47 ,illustration3 ,fig4 #bgg4 ,the smoke shows the rays of light falling on a convex mirror1 and rendered still more divergent4 ,the smoke developes the cone of rays reflected from a concave mirror in the most beautiful manner1 and by producing plenty of ,page #bhi smoke1 and turning the mirror about--the position of the focus 7focus1 a fire-place71 is indicated by a brilliant spot of light1 and the reason the images of objects reflected by the concave mirror are reversed1 may be better understood by observing how the rays cross each other at that point4 7,fig4 #bgh47 ,illustration3 ,fig4 #bgh4 ,the smoke shows rays of light falling on the concave mirror4 ,in this experiment attention should be directed to the bright point1 ,e1 the focus where the convergent rays meet4 ,one of the most perfect applications of the reflection of light is shown in the ,gregorian reflecting telescope1 or in that magnificent instrument constructed by ,lord ,rosse1 at ,parsonstown1 in ,ireland4 7,fig4 #bgi47 ,illustration3 ,fig4 #bgi4 ,lord ,rosse's gigantic telescope4 ,the description of nearly all elaborate optical instruments is somewhat tedious1 but we venture to give one diagram1 with the explanation of the ,gregorian reflecting telescope4 7,fig4 #bhj47 ,illustration3 ,fig4 #bhj4 ,the ,gregorian reflecting telescope4 ,at the bottom of the great tube ,t ,t ,t ,t1 7,fig4 #bhj71 is placed the large concave mirror ,d ,u ,v ,f1 whose principal focus is at ,m2 and in its middle is a round hole ,p1 opposite to which is placed the small mirror ,l1 concave towards the greater one1 and so fixed to a strong wire ,m1 that it may be moved farther from the great mirror or nearer to it1 by means of a long screw on the outside of the tube1 keeping its axis still in the same line ,p ,m ,n with that of the great one4 ,now since in viewing a very remote object we can scarcely see a point of it but what is at least as broad as the great mirror1 we may consider the rays of each pencil1 which flow from every point of the object1 to be parallel to each other1 ,page #bij and to cover the whole reflecting surface ,d ,u ,v ,f4 ,but to avoid confusion in the figure1 we shall only draw two rays of a pencil flowing from each extremity of the object into the great tube1 and trace their progress through all their reflections and refractions to the eye f1 at the end of the small tube t t1 which is joined to the great one4 ,let us then suppose the object ,a ,b to be at such a distance1 that the rays ,e flow from its lower extremity ,b1 and the rays ,c from its upper extremity ,a4 ,then the rays ,c falling parallel upon the great mirror at ,d1 will be thence reflected by converging in the direction ,d ,g2 and by crossing at i in the principal focus of the mirror1 they will form the upper extremity i of the inverted image i ,k1 similar to the lower extremity ,b of the object ,a ,b2 and passing on the concave mirror ,l 7whose focus is at ,n7 they will fall upon it at g and be thence reflected1 converging in the direction ,n1 because g m is longer than g n2 and passing through the hole ,p in the large mirror1 they would meet somewhere about r1 and form the lower extremity d of the erect image a d1 similar to the lower extremity ,b of the object ,a ,b4 ,but by passing through the plano-convex glass ,r in their way they form that extremity of the image at b4 ,in like manner the rays ,e which come from the top of the object ,a ,b and fall parallel upon the great mirror at ,f1 are thence reflected converging to its focus1 where they form the lower extremity ,k of the inverted image i ,k1 similar to the upper extremity ,a1 of the object ,a ,b2 and passing on to the smaller mirror ,l and falling upon it at h1 they are thence reflected in the converging state h o2 and going on through the hole ,p of the great mirror1 they would meet somewhere about q1 and form there the upper extremity a of the erect image a d1 similar to the upper extremity ,a of the object ,a ,b2 but by passing through the convex glass ,r1 in their way1 they meet and cross sooner1 as at a1 where that point of the erect image is formed4 ,the like being understood of all those rays which flow from the intermediate points of the object1 between ,a and ,b1 and enter the tube ,t ,t1 all the intermediate points of the image between a and b will be formed2 and the rays passing on from the image through the eye-glass ,s1 and through a small hole e in the end of the lesser tube t t1 they enter the eye f which sees the ,page #bia image a d 7by means of the eye-glass71 under the large angle c e d1 and magnified in length1 under that angle1 from c to d4 ,to find the magnifying power of this telescope1 multiply the focal distance of the great mirror by the distance of the small mirror1 from the image next the eye1 and multiply the focal distance of the small mirror by the focal distance of the eye-glass2 then divide the product of the latter1 and the quotient will express the magnifying power4 7,fig4 #bhj47 ,we now come to that much disputed and often quoted experiment of ,archimedes1 who is stated to have employed metallic concave specula or some other reflecting surface by which he was enabled to set fire to the ,roman fleet anchored in the harbour of ,syracuse1 and at that time besieging their city1 in which the great and learned philosopher was shut up with the other inhabitants4 ,the story handed down to posterity was not disputed till about the seventeenth century1 when ,descartes boldly attacked the truth of it on philosophical grounds1 and for the time silenced those who supported the veracity of this ancient ,joe ,miller4 ,nearly a hundred years after this time1 the neglected ,archimedes fiction was again examined by the celebrated naturalist ,buffon1 and the account of his experiments detailed by the author of ,adversaria1 in ,chambers' ,journal1 is so logical and conclusive1 that we give a portion of it verbatim4 ,for some years prior to #agdg1 the ,french naturalist ,buffon had been engaged in the prosecution of those researches upon heat which he afterwards published in the first volume of the ,supplement to his ',natural ,history4' ,without any previous knowledge1 as it would seem1 of the mathematical treatise of ,anthemius 7,greek3 peri paradoxn mchanmatn71 in which a similar invention of the sixth century is described1,g ,buffon was led1 in spite of the reasonings of ,descartes1 to conclude that a speculum or series of specula might be constructed sufficient to obtain results little1 if at all1 inferior to those attributed to the invention of ,archimedes4 ,footnote ,g3 ,see ,gibbon's ,decline and ,fall1 chap4 xl41 section v41 note g4 ,this1 after encountering many difficulties1 which he had foreseen with great acuteness1 and obviated with equal ingenuity1 he at length succeeded in effecting4 ,in the spring of #agdg1 he laid before the ,french ,academy a memoir which1 in his collected works1 extends over upwards of eighty pages4 ,in this paper1 he describes himself as in possession of an apparatus by means of which he could set fire to planks at the distance of #bjj1 and even #baj feet1 and melt metals and metallic minerals at distances varying from twenty-five to forty feet4 ,this apparatus he describes as composed of #afh plain glasses1 silvered on the back1 each six inches broad by eight inches long4 ,these1 he says1 were ranged in a large wooden frame1 at intervals not exceeding the third of an inch2 so that1 by means of an adjustment behind1 each should be moveable in all directions independently of the rest--the spaces between the glasses being further of use in allowing the operator to see from behind the point on which it behoved the various disks to be converged4 ,page #bib ,these results ascertained1 ,buffon's next inquiry was how far they corresponded with those ascribed to the mirrors of ,archimedes--the most particular account of which is given by the historians ,zonaras and ,tzetzes1 both of the twelfth century4,h ',archimedes1' says the first of these writers1 'having received the rays of the sun on a mirror1 by the thickness and polish of which they were reflected and united1 kindled a flame in the air1 and darted it with full violence on the ships which were anchored within a certain distance1 and which were accordingly reduced to ashes4' ,the same ,zonaras relates that ,proclus1 a celebrated mathematician of the sixth century1 at the siege of ,constantinople1 set on fire the ,thracian fleet by means of brass mirrors4 ,tzetzes is yet more particular4 ,he tells us1 that when the ,roman galleys were within a bow-shot of the city-walls1 ,archimedes caused a kind of hexagonal speculum1 with other smaller ones of twenty-four facets each1 to be placed at a proper distance2 that he moved these by means of hinges and plates of metal2 that the hexagon was bisected by 'the meridian of summer and winter2' that it was placed opposite the sun2 and that a great fire was thus kindled1 which consumed the ,roman fleet4 ,footnote ,h3 ,quoted by ,fabricius in his ,biblioth4 ,grc41 vol4 ii41 pp4 #eea1 #eeb4 ,from these accounts1 we may conclude that the mirrors of ,archimedes and ,buffon were not very different either in their construction or effects4 ,no question1 therefore1 could remain of the latter having revived one of the most beautiful inventions of former times1 were there not one circumstance which still renders the antiquity of it doubtful3 the writers contemporary with ,archimedes1 or nearest his time1 make no mention of these mirrors4 ,livy1 who is so fond of the marvellous1 and ,polybius1 whose accuracy so great an invention could scarcely have escaped1 are altogether silent on the subject4 ,plutarch1 who has collected so many particulars relative to ,archimedes1 speaks no more of it than the former two2 and ,galen1 who lived in the second century1 is the first writer by whom we find it mentioned4 ,it is1 however1 difficult to conceive how the notion of such mirrors having ever existed could have occurred1 if they never had been actually employed4 ,the idea is greatly above the reach of those minds which are usually occupied in inventing falsehoods2 and if the mirrors of ,archimedes are a fiction1 it must be granted that they are the fiction of a philosopher4 ,supposing that ,archimedes really did project the concentrated rays of the sun on the ,roman vessels1 one cannot help pitying the ignorance of the ,admiral ,marcellus4 ,had this officer been acquainted with the laws of the reflection of light1 he might have laughed to scorn the power of ,archimedes1 and by receiving the unfriendly rays on one of the bright brazen convex shields of his soldiers1 ,marcellus could have scattered the concentrated rays1 and prevented the burning of his vessels4 ,in these days of learning it therefore appears strange to find any one advocating the possible use of specula or reflecting mirrors for the purposes of offence or defence1 but ,m4 ,peyrard a few years ago proposed ,page #bic to produce great effects by mounting each mirror in a distinct frame1 carrying a telescope so that one person could direct the rays to the object intended to be set on fire1 and he gravely calculated1 presuming on the ignorance of the attacked1 that with #eij glasses of about twenty inches in diameter1 he could reduce a fleet to ashes at the distance of a quarter of a league6 and with glasses of double that size at the distance of half a mile6 ,what effect a shell or shot would produce upon this ancient weapon is not stated2 this we may safely leave our readers to determine for themselves4 ,the experiment of ,archimedes has long been a favourite one with the boys4 7,fig4 #bha47 ,illustration3 ,fig4 #bha4 ,one of the miseries of reflection4 ,the total internal reflection of light by a column of water is an experiment that admits of great variety so far as colour is concerned1 and is one of the most novel and beautiful experiments with light presented to the public within the last few years4 ,the author had the pleasure of introducing it in the first place at the ,polytechnic ,institution1 where the optical novelty excited the greatest attention1 and received the approbation of her ,most ,gracious ,majesty1 and his ,royal ,highness the ,prince ,consort1 with the ,royal ,family1 who were pleased to pay a private evening visit to the ,polytechnic1 and amongst other things minutely examined the ,illuminated ,cascade1 which had been erected by ,mons4 ,duboscq of ,paris4 ,the illumination of the descending columns of water was obtained by converging the rays from a powerful electric light upon the orifice from ,page #bid which the water escaped1 the ,duboscq lantern already explained being employed1 and in front of it were placed three cylinders1 each having a circular window behind and opposite the lens1 and an aperture of about one inch in diameter on the opposite side for the escape of water4 ,the lantern used was of a peculiar shape1 and had three sides1 the electric light being in the centre of them1 and passing through three separate plano-convex lenses to the three cylinders from which the water escaped4 ,illustration3 ,fig4 #bhb4--;,fig4 #a4 ,a4 ,the electric light4 ,b ,c ,d4 ,the three sides and lenses of the lantern4 ,e ,f ,g4 ,the three cylinders of water1 each with a circular glass window and orifices at ,z ,z ,z1 from which the water and rays of light pass out4--,fig4 #b4 ,h4 ,section of one side of the ,duboscq lantern4 ,i ,i4 ,cylinder of water1 which enters from below4 ,k ,k4 ,the stream of illuminated water4 ,l ,l4 ,bit of coloured glass held between the lantern and the cistern of water4 ,attention may be directed to the fact that the light merely passes out of the orifices as a diverging beam of light until the flow of water commences1 when the rays are immediately taken up and reflected from ,page #bie point to point inside the arched column of water1 and illuminating the latter in the most lovely manner1 it appears sometimes like a stream of liquid metal from the iron furnace1 or like liquid ruby glass1 or of an amethyst or topaz colour1 according to the colours of the plates of glass held between the mouths of the lantern and the circular windows in the cylinders of water4 ,the same experiment created quite a furore at the ,crystal ,palace when it was introduced in one of the author's lectures delivered in that noble place of amusement4 ,in order that our readers may understand the arrangement of the apparatus1 we have given at page #bid a ground plan view of it1 as also the appearance of the cascade when exhibited at the ,polytechnic to the ,royal party4 7,fig4 #bhd47 ,illustration3 ,fig4 #bhc4 ,a ,b4 ,the sides of the cascade4 ,the dotted lines show the reflection of only two rays of the beam of light passing down inside the water4 ,another curious effect observed with the illuminated cascade1 is the descent of balls of light as the reflection is cut off for a moment by passing the finger through the stream of water1 showing that a certain time is occupied in the reflection of light from one end of the cylinder of water to the other2 indeed the best idea of the rationale of the experiment is formed by substituting in imagination a silver tube highly polished in the interior1 for the descending jet of water4 ,the reflection of sound takes place precisely in the same manner1 and the vibrations of the air are reflected from plane1 concave1 and convex surfaces4 ,it is on this principle that waves of sound thrown off from different surfaces 7as of hard rocks71 produce the effect of the echo4 ,the sounds arrive at the ear in succession1 those reflected nearest the ear being first1 and the reflecting surfaces at the greatest distance sending the waves of sound to the ear after the former4 ,at ,lurley ,falls on the ,rhine1 there is an echo which repeats seventeen times4 ,whispering galleries1 again1 illustrate the reflection of sound from continuous curved surfaces1 just as the arched column of water reflects from its interior curved surfaces the rays of light4 ,speaking-tubes are well known in which the waves of sound are successively reflected from the sides1 exactly like the ,illuminated ,cascade 7,fig4 #bhc74 ,the speaking-trumpet is also another and familiar example of the same principle4 ,probably when ,albertus ,magnus constructed the brazen head1 which had the power of talking1 it was nothing more than a metallic head with a few wheels and visible mechanism inside1 but connected with a lower apartment by a hollow metal tube1 where ,albertus ,magnus descended1 and astonished the ignorant with ,page #bif the then unknown principle of the speaking tube4 ,light entering at one end of a bright metallic tube is reflected from the sides of the tube till it reaches the other1 and precisely the same effect occurs in the interior of the cascade of water4 7,fig4 #bhd74 ,illustration3 ,fig4 #bhd4 ,end of ,polytechnic ,hall1 where the illuminated cascade was displayed to her ,majesty1 ,h4,r4,h4 the ,prince ,consort1 and ,royal party4 ,the cascades issued from behind some artificial rock-work4 ,,the ,,kaleidoscope4 ,if this article on light and optics had gone minutely into the mathematical and purely scientific portion of the subject1 we should have had frequent occasion to mention the name of ,sir ,david ,brewster1 a distinguished philosopher1 whose name is peculiarly identified with this interesting branch of physics4 ,it is always pleasing to find men of such standing not only devoting themselves to arguments which college wranglers would study with pleasure1 but also descending to a lower level1 and inventing optical instruments that delight and amuse the non-scientific and juvenile part of the community4 ,the names of ,sir ,david ,brewster and ,professor ,wheatstone have been connected during the last few years with the invention of the stereoscope1 an instrument ,page #bih that will be noticed in another part of this book1 but here we shall describe one of the most original optical instruments ever devised1 and although it is now regarded as a mere toy1 its merits are very great4 ,the title of the instrument is borrowed from the ,greek ,greek3 kalos1 beautiful1 ,greek3 eidos1 a form or appearance1 ,greek3 skope1 to see2 and the public certainly endorsed the name when they purchased #bjj1jjj of these instruments in ,london and ,paris during the space of three months4 ,it is said that the sensation it excited in ,london1 throughout all ranks of the community1 was astonishing1 and people were everywhere seen1 even at the corners of the streets1 looking through the kaleidoscope4 ,the essential parts of this instrument are two mirrors of unsilvered black parallel glass1 or plate glass painted black on one side1 which should be from six to ten inches in length1 and from one inch to an inch and a half in breadth at the object end1 while they are made narrower at the other end1 to which the eye is applied4 ,the mirrors are united at their lower edges by a strip of black calico fixed with common glue1 and are left open at the upper edges1 and retained at the proper angle by a bit of cork properly blackened4 ,the angles are #cf1 #cj1 #be-e_/g1 #bb1 #bj1 #ah1 which divide the circumference into #aj1 #ab1 #ad1 #af1 #ah1 #bj parts1 thus #cf #aj #cfj1 or #ah #bj #cfj1 and the strictest attention must be paid to this part of the adjustment1 or the figures produced will not be symmetrical4 ,after the mirrors are adjusted to ,page #bih the proper angle1 the space between the two upper edges should be covered across with black velvet and the mirrors placed in a tin or brass tube1 so that the broad ends shall barely project beyond the end1 while the narrow end is placed so that the angle formed by the junction of the mirrors shall be a little below the middle of that end of the tube4 ,a cover with a circular aperture in the centre is then to be fitted to the narrow end of the mirrors1 which should in general be furnished with a convex lens whose focal length is an inch or two greater than the length of the mirrors4 ,a case for holding the objects1 and for communicating to them a revolving motion1 is fitted to the object end of the tube4 ,the objects best suited for producing pleasing effects are small fragments of coloured glass1 wires of glass1 both spun and twisted1 and of different colours and shades of colours1 and of various shapes1 in curves1 angles1 circles2 also1 beads1 bugles1 fine needles1 small pieces of lace1 and fragments of fine sea-weed are very beautiful4 ,m4 ,sturm1 of ,prague1 has lately fixed the images of the kaleidoscope1 so that they are available for the production of patterns in every branch of silk1 cotton1 and mixed fabrics4 ,photographs could be taken of the most beautiful of these accidental designs1 which only occur once1 and if not copied are lost4 ,illustration3 ,fig4 #bhe4 ,a ,b4 ,the tube containing the two mirrors1 shown by dotted lines4 ,a4 is the small end where the eye is placed4 ,b4 ,the object end4 ,c ,d4 ,another view of the mirrors arranged to place in the tube2 the shaded portion represents the black velvet4 ,e4 ,double convex lens4 ,f4 ,box to contain objects1 and usually fitted with ground glass outside4 ,,chapter ,,xxii4 ,,the ,,refraction ,,of ,,light4 ,this term appears to be often confounded with that of reflection1 and signifies the bending or breaking back of a ray of light 7re1 back1 and frango1 to break72 and it will be remembered that when light falls on the surface of a solid 7either liquid or gaseous7 body1 it may be reflected 7re1 back1 and flecto1 to bend71 refracted1 polarized1 or absorbed4 ,in the previous chapter the property of the reflection of light has been fully investigated1 and in this one refraction only will be considered4 ,it is a property which has been1 and will continue to be1 of the greatest practical utility in its application to the construction of all magnifying glasses1 whether belonging to the telescope1 microscope1 magic lantern1 or the dissolving views2 or the minor refracting instruments--such as spectacles1 opera-glasses1 c42 and it should be remembered that their magnifying power depends solely on the property of refraction4 ,if substances such as glass had not been endowed with this property1 it would be difficult to understand how the great discoveries in the science of astronomy could have been made1 or what information we could have gained respecting those interesting truths so constantly revealed by the aid of the microscope4 ,numerous instances might be quoted of the value of this latter instrument in the detection of adulteration1 and the examination of organic structures4 ,when so many talented and industrious scientific men are at work with this ,page #bii instrument1 it is perhaps invidious to point to one singly1 though we must make an exception in favour of ,professor ,ehrenberg1 of ,berlin1 whose microscope did such good service in procuring undeniable proof of the ,simonides' fraud2 he has made use of it again to detect the thief that stole a barrel of specie1 which had been purloined on one of the railways4 ,one of a number of barrels1 that should have contained coin1 was found on arrival at its destination to have been emptied of its precious contents1 and re-filled with sand4 ,on ,professor ,ehrenberg being consulted1 he sent for samples of sand from all the stations along the different lines of railway that the specie had passed1 and by means of his microscope identified the station from which the sand must have been taken4 ,the station once discovered1 it was not difficult to hit upon the culprit in the small number of employs on duty there4 ,illustration3 ,fig4 #bhf4 ,the simplest case of refraction occurs in tracing the course of a ray of light through the air1 and into the medium water2 in this case it passes from a rare to a dense medium1 and the fact itself is well illustrated by the next diagram1 in which the shaded portion represents water1 and the paper that it is drawn upon the air4 ,the line ,a ,b is a perpendicular ray of light1 which passes straight from the air into and through the water1 without being changed in its direction4 ,the line ,c ,d is another ray1 inclined from the perpendicular1 and entering the water at an angle1 does not pass in the straight line indicated by the dotted line1 but is refracted or bent towards the perpendicular at ,d ,e4 ,this fact reduced to the brevity of scientific laws is thus expressed3--,when a ray of light falls perpendicularly on a refracting surface1 it does not experience any refraction or change of direction4 ,when light passes out of a rare into a dense medium1 as from air into water1 the angle of incidence is greater than the angle of refraction4 ,and when light passes from a dense into a rare medium1 as out of water into air1 the reverse takes place1 and the angle of incidence is smaller than the angle of refraction4 ,in order to illustrate these laws1 a zinc-worker or tinman may construct a little tank1 with glass windows in the front and sides1 the latter being as deep as the half-circle described on the back metal plate of the tank1 which of course rises higher1 in order to show the full circle2 this should be japanned white1 and a perpendicular and horizontal black line described upon it--the whole1 with the exception of the circle1 being japanned black4 ,if the ,duboscq lantern is arranged with the little mirror1 as described in fig4 #bgf1 page #bhg1 the ray of light may be thrown perpendicularly1 or at an angle1 through the water1 ,page #cjj and the actual breaking back of the ray of light is rendered distinctly apparent4 7,fig4 #bhg47 ,illustration3 ,fig4 #bhg4 ,a4 ,duboscq lantern4 ,b4 ,the mirror4 ,b ,c4 ,the incident ray4 ,c ,d4 ,the refracted ray4 ,e ,f4 ,tank1 containing water up to the horizontal line of the circle4 ,the refraction of light is also well displayed by ,duboscq's apparatus1 with the plano-convex lens1 and a brass arrow as an object1 with another double convex lens to focus it4 ,when a good sharp outline of the arrow is obtained on the disc1 a portion of the rays of light producing it may then be truly broken out or refracted by laying across the brass arrow a square bar of plate glass4 7,fig4 #bhh74 ,illustration3 ,fig4 #bhh4 ,a4 ,rays of light from the electric light4 ,b4 ,the cap1 with figure of arrow cut out4 ,c4 ,the bar of plate glass4 ,d4 ,the double convex glass to focus ,e1 the image on the disc1 and portion refracted at ,b4 ,there are many simple ways in which the refraction of light is displayed1 such as the apparent breaking of an oar where it enters the water1 or the remarkable manner in which the bottom is lifted up when we look1 at any angle1 through the clear water of a deep river or lake2 the latter circumstance has unhappily led to most serious accidents1 in consequence of children being induced by the apparent shallowness of ,page #cja the water to get in and bathe4 ,fish1 again1 unless seen perpendicularly from a boat1 always appear nearer than their true position1 and the ,indians1 when they spear fish1 always take care to strike as near the perpendicular as possible2 experienced shots know they must aim a little lower and nearer than the apparent position of a fish in order to hit it4 ,having learnt that light is bent from its course1 it might be supposed that all objects looked at through plate glass should appear distorted2 but it must be remembered that the sides of the glass being nearly parallel1 an equal amount of refraction occurs in every direction--so that1 unless the window is glazed with uneven wavy glass1 the object1 for all practical purposes1 does not apparently change its position1 being neither moved to the right or the left1 or upward or downward4 ,in order to bend the rays of light in the required direction1 the glass must be cut into certain figures called prisms1 plane glasses1 spheres1 and lenses1 some of which are shown in the annexed cut4 7,fig4 #bhi47 ,illustration3 ,fig4 #bhi4 ,illustration3 ,fig4 #bij4 ,a ,b4 ,a double convex lens4 ,c is a ray of light1 which falls perpendicularly on ,a ,b1 and therefore passes on straight to ,f1 the focus4 ,d ,d4 ,rays falling at an angle on ,a ,b1 refracted to focus1 ,f4 ,it would be tedious to trace out1 by a regular series of diagrams1 the passage of light through the variety of combinations of lenses2 and as the plane1 convex1 and concave surfaces have been examined with respect to their effect on the reflection of light1 they may be referred to again with regard to their influence in refracting light4 ,in the latter it will be found that convex and concave lenses have just the opposite properties of mirrors2 thus1 a convex lens receiving parallel rays will cause them to converge to a focus4 7,fig4 #bij47 ,the case of short-sighted persons arises from too great a convexity of the eye1 which makes a very near focus2 and that of old people is a flattening of the eye1 by which the focus is thrown to a greater distance4 ,the remedy for the latter is a convex spectacle-glass1 whilst a concave lens is required for the former1 to scatter the rays and prevent their coming to a point too soon4 ,page #cjb ,the action of a concave refracting surface is again the opposite to a concave reflecting surface--the former disperses the rays of light1 whilst1 the latter collects them4 ,a concave lens1 as might be expected1 produces exactly the contrary effect on light to that of a concave mirror4 7,fig4 #bia47 ,illustration3 ,fig4 #bia4 ,a ,b4 ,a double concave lens4 ,c41 is a ray of light which falls perpendicularly on ,a ,b1 and passes through without any alteration of its course4 ,d ,d4 ,rays falling at an angle on ,a ,b1 are refracted and diverged4 ,these facts are well shown with the aid of the lantern and electric light4 ,the rays of light are refracted in a visible manner when received on a concave or convex lens1 provided a little smoke from paper is employed1 as in the mirror experiments4 7,fig4 #bib47 ,illustration3 ,fig4 #bib4 ,a4 ,the electric light4 ,b4 ,the lens4 ,bearing these elementary truths in mind1 it will not be difficult to follow out a complete set of illustrations explanatory of the construction and use of various popular optical contrivances4 ,page #cjc ,,chapter ,,xxiii4 ,,refracting ,,optical ,,instruments4 ,i4 ,the ,magic ,lantern4 ,no other optical instrument has ever caused so much wonderment and delight1 from its origin to the present time1 as this simple contrivance4 ,for a long time its true value was overlooked1 and only ridiculous or comic slides painted1 but its educational importance is now being thoroughly appreciated1 not only on account of the size of the diagrams that may be represented on the disc1 but also from the fact that the attention of an audience is better secured in a room when the only object visible is the diagram under explanation4 ,the lenses it contains are a bull's eye or plano-convex1 nearest the light1 and a double convex glass1 for the purpose of focussing the picture which is inverted and placed between the two lenses4 7,fig4 #bic47 ,illustration3 ,fig4 #bic4 ,the magic lantern4 ,in many books full directions are given for painting the glass slides1 but this is an art that requires very great practice and experience4 ,a person may know how to draw and paint on paper or canvas1 but it is quite a different thing where glass is concerned1 and unless the juvenile artist has taken lessons from a regular painter on glass1 his or her efforts are likely to be very unsatisfactory4 ,in many popular works embracing the subject of optics1 full directions are given on the mode of painting the slides for the magic lantern1 or dissolving views2 a new era1 however1 has dawned upon this mode of illustration1 in the preparation of photographs on glass of the most lovely description1 and now instead of exhibiting mere daubs of weak colouring1 photographic pictures of singular perfection can be procured of ,messrs4 ,negretti and ,zambra1 ,holborn1 who have turned their attention especially to this branch1 and supply slides of all sizes4 ,,ii4 ,the ,dissolving ,views4 ,this very pleasing modification of the ordinary magic lantern is displayed with the assistance of two lanterns of the same size1 provided with lamps and lenses which are exactly alike4 ,they are best arranged ,page #cjd on one board1 side by side1 and if kept parallel with each other1 the circles of light thrown from the two lanterns would not coincide on the screen2 it is therefore necessary to place one of them at an angle which will vary according to the distance from the screen4 ,the task of making the two circles of light overlap each other precisely on the disc1 is called centering the lanterns1 and is the first thing that must be attended to before exhibiting the slides4 ,the slides for the dissolving views are all painted of the same size1 and supposing a scene such as a church with a bridal procession and the trees in full foliage1 to represent summer1 is first thrown on to the disc1 it may be changed to winter by putting another picture of the same subject1 but painted to represent bare trees1 and the church and ground covered with snow1 and a grave open1 with a funeral procession4 ,the two pictures must not be projected on the screen at the same time1 and here the dissolving mechanism is required2 it consists of two fans so arranged that they may be raised or lowered by a rack-work and handle2 one fan in descending covers one of the nozzles of the lanterns1 and the other leaves the second lantern open1 and free to project the picture2 the dissolving is managed by slowly moving the handle of the rack-work1 so that one quarter of the picture already on the disc is cut off1 and one quarter of the new one thrown on4 ,as the movement proceeds1 one half of the old picture is shut out1 and one half of the new slide takes its place1 and so on1 till the whole of the original picture is cut off by the fan and the new one comes into view1 and it is in this way the effect of the change from summer to winter is produced4 7,fig4 #bid47 ,illustration3 ,fig4 #bid4 ,nozzle of one lantern1 with the fan1 ,a1 raised1 and in the position to throw a picture on the disc4 ,b4 ,the other fan shutting off the second lantern4 ,when two pictures such as those already described1 dissolve one into the other1 of course the same building or other marked portion of the subject1 must strictly coincide in each picture on the disc1 or else the two pictures are apparent1 and the illusion is destroyed4 ,the pictures must all be centered before the exhibition commences4 ,by the arrangement of ,mons4 ,duboscq1 one electric light serves to illuminate both lanterns by making use of mirrors4 ,the dissolving apparatus is likewise very ,page #cje simple1 and consists of two diamond-shaped openings in a brass frame1 which open and shut alternately by a slide worked with a handle4 ,the single light is not to be recommended1 as it is somewhat troublesome to manage properly4 7,fig4 #bie47 ,illustration3 ,fig4 #bie4 ,a4 ,the electric light4 ,b ,b4 ,the two sets of lenses for the two pictures4 ,c4 ,the dissolving mechanism4 ,d4 ,the picture on screen4 ,when dissolving views are required on a grand scale1 the lenses must be exceedingly large1 and the condenser 7corresponding with the bull's-eye of the simple magic lantern7 should be at least nine or eleven inches in diameter1 and the front glasses must be of a superior make4 ,the lenses for a large lantern lit by the oxy-hydrogen light1 are arranged as in the next cut4 7,fig4 #bif47 ,illustration3 ,fig4 #bif4 ,a4 ,the lime light4 ,b4 ,the condensers4 ,c4 ,the picture4 ,d ,d4 ,the front lenses for focussing1 with rack-work4 ,at the ,polytechnic the author had no less than six lanterns working at or about the same time1 to produce effects1 in the views illustrating the voyages of ,sinbad the ,sailor2 and in order to obtain the increased ,page #cjf results required for dioramic effects1 such for instance as the ,siege of ,delhi1 showing the bursting of the shells1 c41 the four fixed lanterns 7the fronts of which are shown in the next cut7 were always employed4 ,the two upper lanterns are dissolved by discs of brass worked by the hand1 and the lower ones with the fans4 7,fig4 #big47 ,illustration3 ,fig4 #big4 ,fronts of the four lanterns1 showing how the dissolving mechanism is arranged4 ,behind the scenes always has a great attraction for young people2 we have1 therefore1 in the frontispiece1 with the help of ,mr4 ,hine 7who painted a great number of the photographs shown at the ,polytechnic during the author's management71 given a section of the large theatre taken whilst the effective scene of the ,siege of ,delhi was in progress4 ,the optical effects were assisted by various sounds in imitation of war's alarms1 for the production of which1 more volunteers than were required would occasionally trespass behind the screen1 and produce those terrific sounds that some persons of a nervous temperament said were really stunning4 ,in a page picture1 we have also given a correct drawing of the interior of the optical box at the ,polytechnic1 with the four fixed lanterns1 and side cupboards to hold the glass pictures4 ,the four lanterns worked on a railway1 with wheels and a circular turn-table2 they could be removed1 and the microscope arranged in their places4 ,illustration3 ,before and behind the screen at the ,polytechnic during the exhibition of the dioramic effects of the siege of ,delhi4 p4 #cjf ,page #cjg ,,iii4 ,the ,oxy-,hydrogen ,microscope4 ,many persons will recollect the first exhibition of this instrument in ,bond-street1 by ,mr4 ,j4 ,t4 ,cooper1 and ,mr4 ,cary1 succeeded by the ,adelaide ,gallery exhibition of scientific wonders and an oxy-hydrogen microscope4 ,the apparatus for this purpose consists of three condensing lenses and an object glass4 ,the objects1 such as live aquatic insects1 are placed in glass troughs containing water2 the other objects1 ferns1 feathers1 butterflies1 alg1 c4 c41 being mounted on slides in the ordinary way with ,canada balsam4 7,fig4 #bih47 ,illustration3 ,fig4 #bih4 ,a4 ,the lime light4 ,c ,c ,c4 ,condensers4 ,d4 ,the object1 such as a tank of water containing live insects4 ,e4 ,the object glasses4 ,,iv4 ,the ,physioscope4 ,this instrument1 brought out at the ,polytechnic during the time that ,mr4 ,j4 ,f4 ,goddard managed the optical department of the institution1 always excited the greatest mirth and astonishment amongst the numerous visitors2 and habitus of the old place may remember the good-natured inimitable maudlin simper with which poor ,mr4 ,tait 7who was one of the living objects shown on the disc7 used to drink off the glass of wine and then wink at the audience4 ,when we say ,mr4 ,tait used to wink1 of course it is understood that he was personally invisible1 and his apparition or image only appeared on the disc4 ,the countenance is brilliantly illuminated by the oxy-hydrogen light1 and being placed near the lenses1 the rays are reflected from the face into the physioscope1 and being properly focused1 and the inversion of the image corrected1 the perfect representation of the human countenance is apparent on the disc4 ,the lenses and concave reflectors required are shown in the section of the physioscope4 ,messrs4 ,carpenter and ,westley1 of ,regent-street1 have brought the manufacture of magic lanterns to great perfection2 and ,mr4 ,collins1 of the ,polytechnic1 constructs every kind of dissolving view apparatus1 oxy-hydrogen microscopes1 physioscopes1 c4 7,fig4 #bii47 ,with this instrument any opaque objects 7provided they reflect light properly7 may be displayed to a large audience4 ,plaster casts appear with singular beauty and softness1 whilst flowers1 stuffed birds1 and especially humming birds1 are excellent objects for the physioscope4 ,page #cjh ,illustration3 ,fig4 #bii4 ,a4 ,one or more lime lights1 throwing rays reflected by concave mirrors on to the face ,b1 from whence they are reflected to ,c ,c1 the first condensers4 ,d ,d4 ,object glasses4 ,this instrument is made by ,mr4 ,collins1 who has the tools for making the reflectors with correct curves4 ,the picture of the face on the disc is covered with black spots if the reflectors are not perfect4 ,v4 ,the ,camera ,obscura4 ,a dark chamber is the name of a most amusing1 and now1 in the improved form1 extremely valuable instrument for photographic purposes4 ,it is occasionally to be met with in public gardens1 and there is a very good one on the ,hoe at ,plymouth4 ,the construction of the camera for observing the surrounding country is very simple1 and merely consists of a flat mirror placed at an angle1 by which the picture is reflected through a double-convex lens on to a white table beneath4 7,fig4 #cjj47 ,illustration3 ,fig4 #cjj4 ,a4 ,the mirror4 ,b4 ,the convex lens4 ,c4 ,the white table4 ,page #cji ,the term focusing1 or the art of moving the lenses so that a sharp image may be obtained1 has been frequently mentioned in this article1 and perhaps it may be as well to describe the mode of ascertaining the focal distance of a lens by experiment4 ,hold the lens opposite the window so that a bright picture of the window-sash may be obtained on a sheet of paper pinned against the wall1 and the distance of the lens from the paper will be the focal length4 ,if the lens has a very long focal length1 it may be determined as follows3--,measure the distance between the lens and the object1 and also from the image2 multiply these distances together1 and divide the product by their sums2 the quotient will give the focal distance4 ,,vi4 ,the ,decomposition of ,light--its ,analysis and ,synthesis4 ,it is in the ,italian language that the bride1 the emblem of purity1 is called ,lucia 7,lux1 light72 and surely if an illustration were required of beauty and singleness1 light would be named poetically as appropriate2 but physically it is not of a single nature1 it is composite1 and made up of seven colours4 ,the instrument required to refract a ray of light sufficiently to break it into its elementary colours is called the prism1 and is a solid having two plane surfaces1 called its refracting surfaces1 with a base equally inclined to them4 7,fig4 #cja47 ,illustration3 ,fig4 #cja4 ,the prism4 ,the base1 ,a ,b1 is equally inclined to the refracting surfaces1 ,c ,a1 ,c ,b4 ,it was in #afgb that ,sir ,isaac ,newton made his celebrated analysis of light1 by receiving a sunbeam 7as it passed through a hole in a shutter7 on to the refracting surface of a prism1 and throwing the image or spectrum on to a screen1 where he observed the seven colours1 red1 orange1 yellow1 green1 blue1 indigo1 and violet1 and thus proved that there are different species of light1 and that each species is disposed both to suffer a different degree of refrangibility in passing out of one medium into another1 and to excite in us the idea of a different colour from the rest2 and that bodies appear of that colour which arises from the composition of those colours the several species they reflect are disposed to excite4 ,sir ,isaac ,newton's name would have been immortalized by this discovery alone1 even if he had not possessed that transcendent ability which raised him above all other mathematicians and physicists4 ,it is at the same time interesting to know that the ancient author ,claudian 7,a4,d4 #dbj7 inquires whether colour really belongs to the substances themselves1 or whether by the reflection of light they cheat the eye--enquires sitve color proprius rerum1 lucisne repulsa eludant aciem4 ,sir ,isaac ,newton determined that the spectrum could be divided into #cfj equal parts1 of which red occupied #de1 orange #bg1 yellow #dh1 green #fj1 blue #fj1 indigo #dj1 violet #hj4 ,he also discovered that if the highly refracted rays1 the seven colours1 or spectrum were received into ,page #caj a concave mirror or a double-convex lens1 that they again united and formed white light4 ,in order to demonstrate the properties of the prism in various positions1 the next diagram may be adduced4 7,fig4 #cjb47 ,illustration3 ,fig4 #cjb4 ,a4 ,the ray of light passing through two prisms ,b placed base to base4 ,in this position the light passes through to the second prism1 ,c1 without alteration4 ,at ,c the decomposition of light occurs1 and the spectrum is shown at ,d ,d4 ,the top prism at ,b used singly would reflect the ray to ,e without decomposing it into the coloured rays4 ,the rainbow is the most beautiful natural optical phenomenon with which we are acquainted2 it is only seen in rainy weather when the sun illuminates the falling rain1 and the spectator has the sun at his back4 ,there are frequently two bows seen1 the interior and exterior bow1 or the primary and secondary1 and even within the primary rainbow1 and in contact with it1 and outside the secondary one1 there have been seen other bows beyond the number stated4 ,the primary or inner rainbow consists of seven different coloured bows1 and is usually the brightest1 being formed by the rays of light falling on the upper parts of the drops of rain4 ,the exterior bow is formed by the rays of light falling on the lower parts of the drops of rain2 and in both cases the rays of light undergo refraction and reflection1 hence the opinion of ,aristotle1 that the rainbow is caused only by the reflection of light1 is not correct4 ,the first refraction occurs when the rays of light enter1 and the second when they emerge from the spheroids of water in the first bow2 the refracted rays undergo only one reflection1 whereas in the second the brilliancy of the colours is impaired by two reflections4 ,the spectrum from the electric light is one of the most gorgeous exhibitions of colour that can be conceived2 and the instruments required for the purpose are illustrated in ,no4 #a 7,fig4 #cjc71 whilst the ,page #caa synthesis of the coloured rays and production of white light is shown at ,no4 #b of the same figure4 7,fig4 #cjc47 ,illustration3 ,fig4 #cjc4 ,no4 #a4 ,a4 ,the electric light4 ,b4 ,the narrow slit through which the light passes to the convex lens1 ,c4 ,d4 ,the prism4 ,e4 ,the spectrum4 ,no4 #b is the same for ,a ,b ,c ,d2 but ,f is the convex lens collecting the scattered rays1 and forming white light at ,g4 ,,vii4 ,duration of the ,impression of ,light4 ,if a circular disc is painted with the prismatic colours taken in the same proportion with respect to each other in which they are exhibited in the spectrum made by the prism1 and the wheel is turned swiftly1 then the individual colours disappear1 and nearly white light is apparent4 ,the cause is due to the same principle that creates the appearance of a complete circle of fire when a burning squib is moved quickly round before it is thrown away to burst1 and as it is evident that the burning squib cannot be in every part of the circle at the same moment1 there must be some inherent faculty belonging to the human eye which enables it to retain for a definite period the impression of images that may fall upon it2 and this principle has been so far pressed1 as it were1 beyond its limits1 that it is gravely asserted the image of a man's murderer might be discovered on the retina of the eye-ball if that could be examined sufficiently quick after death4 ,the fixture of the picture is said to be due to a sort of natural photographic process2 but such fanciful statements often lead the mind into dream-land only1 and so we will return to the fact of the duration of the impression of light on the eye as evidenced by several ingenious optical instruments1 and especially by the scientific inventions of ,dr4 ,faraday1 ,dr4 ,paris1 and of ,mr4 ,thomas ,rose of ,glasgow4 ,by careful experiment ,m4 ,d',arcy found that the light of a live coal moving at the distance of #afe feet1 maintained its impression on the ,page #cab retina during the seventh part of a second4 ,hence the cause of the recomposition of white light when the colours on the disc are quickly rotated4 ,each colour at any point succeeds the other before the impression of the last is gone from the eye1 and provided the colours move round within the seventh part of a second1 they are all impressed together on the eye1 and meeting on the retina1 produce the effect of white light4 ,,viii4 ,the ,phenakistiscope4 ,this amusing instrument consists of a turning wheel upon which figures appear to jump1 walk1 or dance4 ,the disc or wheel is of cardboard1 upon which are painted 7towards the periphery7 figures in eight1 ten1 or twelve postures4 ,thus1 if it is desired to represent clowns turning round in a circle1 twelve different positions of the figure in the act of turning are painted on the disc1 and above each of the figures on the wheel a slit is cut about one inch long1 and a quarter of an inch wide in a direction corresponding with the radii of the circle4 ,this simple form of the instrument is used by placing the figured side towards a looking-glass and then causing it to revolve at a certain speed1 which is ascertained by experiment2 and as the spectator looks through the slits into the looking-glass1 the clowns appear to turn round4 ,at the ,polytechnic ,institution there are two of these wheels with looking-glasses1 and although the same designs have done duty for many years1 they still attract the public attention4 7,fig4 #cjd47 ,illustration3 ,fig4 #cjd4 ,design for the phenakistiscope4 ,the spectator is supposed to be looking towards a mirror through the slits4 ,it is supported by a handle through the centre1 round which it is twirled by the other hand4 ,in the ,journal of the ,royal ,institution ,mr4 ,faraday has described some very interesting experiments and optical illusions produced by the revolution of wheels in different directions and velocities4 ,the wheels are made of cardboard1 and by cutting out two cog wheels of an equal size1 and placing one above the other on a pin1 the usual hazy tint when the cogs are acting is apparent when they are whirled round2 but if the two cog wheels are made to move in opposite directions1 there will be the extraordinary appearance of a fixed spectral wheel4 ,if the cogs are cut in a slanting direction on both wheels1 the spectral wheel will exhibit slanting cogs2 but if one wheel is turned so that the cogs shall point in opposite directions1 then the spectral wheel will have straight cogs4 ,a number of such wheels set in motion in a darkened room1 and illuminated suddenly with the light from the electric spark1 appear to stand perfectly still1 although moving with a great velocity4 ,an expensive instrument has been constructed by ,duboscq1 for the ,page #cac purpose of showing the usual phenakistiscope effects on the screen with the magic lantern2 a very limited picture1 however1 is shown1 and there is still great room for the improvement of the apparatus4 7,fig4 #cje47 ,illustration3 ,fig4 #cje4 ,phenakistiscope made by ,duboscq1 of ,paris4 ,no4 #a4 ,apparatus in elevation with the condensers4 ,no4 #b4 ,section of the apparatus4 ,a4 ,the light4 ,b4 ,condenser1 or plano-convex lens4 ,c4 ,round glass disc with design painted on it4 ,d4 ,wooden disc with four double-convex lenses placed at equal distances from each other1 so as to coincide with ,c1 whilst rotating4 ,both the latter and ,c rotate1 and the picture is focussed on the disc by the lenses ,f4 ,no4 #c4 ,glass plate1 with device painted thereon4 ,page #cad ,,ix4 ,the ,thaumatrope4 ,this very simple toy was invented by the late ,dr4 ,paris1 who gave it an appropriate name1 compounded of the ,greek words1 ,greek3 thauma1 wonder1 ,greek3 trep1 to turn4 ,the duration of the impressions of light on the eye is very apparent whilst using this toy1 which is usually made of a circular piece of cardboard1 having on one side a painting of a man's head1 and on the other a hat2 or a picture of a lighted candle on one face of the cardboard1 and an extinguisher on the other2 or a gate1 and a horseman leaping it4 ,each pair of designs painted on opposite sides of the cardboard appear to be one when twisted round by strings tied to the opposite edges of the cardboard circle4 ,the rationale of this experiment being1 that the picture of one design--such as the head and face--is retained by the eye until the hat appears1 and being mutually impressed upon the nerve of vision at very nearly the same instant of time1 they appear as one picture4 ,x4 ,the ,kalotrope4 ,this is an optical arrangement by ,mr4 ,thomas ,rose1 of ,glasgow1 primarily designed for showing the illusions of the phenakistiscope and kindred devices to a numerous audience2 but more remarkable for its presentations of very beautiful spectra1 composed of the multiplication1 combination1 and involution of simple figures disposed around a disc4 ,the arrangement consists of a movement for giving considerable velocity to two concentric wheels1 working nearly in contact1 and moving in contrary directions4 ,but the only part of the apparatus that requires special explanation and illustration is the device disc and the disc of apertures2 the first of which is placed on the hinder wheel1 and the second on the front wheel4 ,we give figures of the two discs1 premising1 however1 that each is capable of an almost infinite variety of characters4 ,no4 #a 7,fig4 #cjf7 presents in its four quadrants the perforations for four distinct discs of apertures2 and ,no4 #b is a device disc1 consisting of twelve equidistant black balls4 ,under a the balls will be presented as twenty-four ovals2 under b1 as forty-eight involved figures1 beautifully variegated2 under c1 as an elaborate lacework2 and under d1 as a rich variegation of form and colour4 ,every fresh disc of devices and disc of apertures of course opens up a new field of effect4 ,thus1 if we take a disc bearing twelve repeats of a ball in the interior of a ring1 each repeat being so painted that its position is advanced in the ring until it reaches in the twelfth ring the point whence it started1 and place this on the back disc of the kalotrope1 having previously removed the first one1 no effect is observed when the wheel is rotated beyond the spreading out of the design and general appearance of hazy black circles4 ,when1 however1 the disc1 with twelve slits or apertures1 is now placed on the front wheel1 and the two rotated in opposite directions1 then the whole figure starts as it were into existence1 and each ball apparently moves round the interior of its circle4 ,page #cae ,the apparatus was produced at the ,royal ,polytechnic ,institution by the author1 and excited much interest4 7,fig4 #cjf47 ,illustration3 ,fig4 #cjf4 ,nos4 #a and #b are the discs4 ,no #c4 ,kalotrope in elevation4 ,no4 #d4 ,side view of kalotrope1 showing the multiplying wheels and the perforated and painted discs moving in opposite directions4 ,,xi4 ,the ,photodrome4 ,this is a second optical arrangement by ,mr4 ,rose for showing spectral illusions2 and it is superior to the last1 inasmuch as it offers to the public lecturer a most effective means of presenting these deceptions to a large audience4 ,it differs from the kalotrope in several important points4 ,it dispenses with the discs of apertures1 and leaves the device disc with its face fully exposed to the spectators4 ,the effects are produced by a powerful light1 thrown through the tube of a lantern1 and broken by a wheel working across it4 ,the apparatus1 as it at present stands in the inventor's possession1 consists of two distinct parts2 the one a movement for the device discs1 and the other for the light4 ,a wheel four feet in diameter is connected with a train of movement capable of giving it five hundred or six hundred revolutions per minute4 ,on this wheel the device disc is placed1 in full view of the spectators1 and set in motion4 ,from an opposite gallery the light is thrown1 and ,page #caf broken by a wheel of such diameter and number of apertures as will admit the velocity of the photodrome 7or light-runner7 to be at least six times the velocity of the device disc2 whilst the apertures are of such width as to restrict the duration of the light-flash to about one-two-thousandth of a second4 ,the wheel working across the light has a train of movement for raising the velocity to two thousand revolutions per second4 ,the management of the apparatus is very simple4 ,the device-wheel is brought to a steady1 rapid rotation1 and the operator on the light then works his wheel with gradually increasing velocity1 until he overtakes the figures of the device1 where1 by mere delicacy of touch1 he is able to hold them stationary or give them motion1 at pleasure4 ,theories of light and colour still agitate the scientific world1 although that man must be bold who will assert that his hypothesis is fitted to explain every difficult point that arises as our experimental knowledge increases4 ,mr4 ,g4 ,j4 ,smith1 of the ,perth ,academy1 has propounded a very ingenious theory of light and colour1 supported by some clever experiments4 ,but1 as ,solomon says1 there is nothing new under the sun1 and in an able paper ,mr4 ,rose1 of ,glasgow1 lays claim to the anticipations of ,mr4 ,smith's theory as follows3-- ,my attention has been directed to a paper entitled ',the ,theory of ,light1' by ,g4 ,john ,smith1 ,esq41 ,m4,a41 of ,perth ,academy4 ,i think it is now nearly two years since ,i communicated an interesting fact to ,professor ,faraday1 and to a member of our local ,philosophical ,institution1 which may fairly claim to have anticipated ,mr4 ,smith's theory4 ,the fact was this3 that if a piece of intensely white card be held in one hand1 with the light of a powerful gas-jet falling upon it1 and if the other hand has command of the gas-tap1 as the light is gradually reduced1 the card will assume the prismatic colours down to intense blue1 and as the light is restored the colours will present themselves in inverse order4 ,the experiment showed1 very conclusively to my mind1 that light is homogeneous1 and that what we name colour is only the various affection of the optic nerve by a greater or lesser radiation of light from a focal point in an imperfect reflector--say1 in the instance1 a white card4 ,i apprehend that ,mr4 ,smith confuses his theory when he speaks of alternations of light and shadow producing colour4 ,shadow1 or darkness1 is mere negation of light4 ,we do not see mixtures of light and darkness1 or blackness and whiteness1 but light in its several degrees of intensity4 ,mr4 ,smith's experiments present only what my kalotrope has done1 and what my later device1 the photodrome 7now nearly three years old7 is doing in a much more perfect manner4 ,it is one of the mysteries intelligible only to the initiated1 that whilst ,mr4 ,smith's paper seems to have been received with great favour by the ,british ,association1 my communication relative to the photodrome was voted 'not sufficiently practical4' 99 99 99 99 99 ,since ,i have come before the public with an experiment1 which in any view is an interesting one1 permit me to reproduce it under several distinct conditions1 and to add a brief narrative of remarkable presentations of colour that have come before me1 and which1 so far as ,i am ,page #cag aware1 are perfectly novel1 or known only through the more recent experiments of ,mr4 ,smith4 ,professor ,faraday very courteously acknowledged my communication of the experiment with the card1 but said that it only partially succeeded with him1 and added that probably this was owing to some decay of sensitiveness in his eyes4 ,more likely ,i failed to state with sufficient clearness the conditions of the experiment1 since ,i have always found nine persons out of ten perfectly agreed as to the effects produced when they have been at my side4 ,the transitions from white to yellow1 orange1 red1 and thence to intense blue1 are1 ,i may say1 invariably admitted4 ,success depends on a very slow and regular reduction and restoration of the light4 ,i have given one method of performing the experiment1 and will add other two4 ,allow the light to remain undisturbed1 and begin by holding the card near to it2 then keep the hand steady and the eye intently fixed upon the card1 and retire gradually with your back to the light1 and the colours will change in the order of the prismatic spectrum from yellow to intense blue4 ,on returning backwards towards the light the colours will again present themselves1 but in inverse order4 ,in this form of the experiment we are certain that the light remains precisely the same throughout4 ,the third method is this3 ,place a circle of white card1 about three inches in diameter1 in the centre of a black board1 and let a spectator stand within twelve inches of the board1 with his eyes fixed upon the card4 ,let an operator be provided with a light so covered that it shall not fall on the eye of the spectator2 then1 as he retires with the light or returns with it1 the spectator will see the colours as before4 ,this arrangement evidently subjects the experiment to a severe test1 since the black board enhances the whiteness of the card1 and tends to preserve it4444 ,whilst pursuing my principal object1 ,i frequently noticed most remarkable presentations of colour2 but1 as the conditions were for the most part unsuitable to the lecture-room1 ,i gave them only a passing regard4 ,allow me to instance a few of the experiments4 ,the first refers to the kalotrope1 which may be briefly described as an arrangement of two concentric wheels1 working nearly in contact and in contrary directions4 ,discs of various devices are provided for the hinder wheel1 and a number of perforated black discs for the one in front4 ,when a disc charged with twelve black radii is placed on the hinder wheel1 the six spokes of the front wheel1 in passing rapidly across it1 convert the twelve black radii into twenty-four apparently stationary white radii upon a tinted ground4 ,here is a remarkable presentation of the complementary1 inasmuch as it is placed permanently before the eye by persistence4 ,the second experiment is performed with the photodrome1 which consists of an independent wheel to receive the device discs1 and an apparatus 7altogether apart1 and1 if desired1 out of sight7 by which flashes of light are thrown upon the disc in rapid and regular succession4 ,now1 if a disc charged with twelve dark blue balls1 nearly in contact1 be placed upon the wheel1 and a little natural light be allowed to fall ,page #cah upon it1 so soon as it is thrown into rapid revolution1 and flashes of artificial light 7insulated in a lantern7 are duly measured out upon it1 we see twelve apparently stationary light-blue balls upon a zone of bright orange4 ,here1 again1 there is nothing for which we are not prepared2 the complementary is suddenly presented1 and it is maintained permanently before the eye by persistence4 ,a third experiment may prove interesting in its relation to ,mr4 ,smith's ingenious theory4 ,place the kalotrope opposite a bright northern noonday sky1 remove the front wheel1 and affix to the hinder wheel one of the perforated black discs used for the kalotropic effects4 ,the experimentalist stands at the back of the instrument1 and can see the sky only through the apertures in the black disc4 ,cause these apertures to pass the eye at intervals varying from one-half to one-sixth of a second1 and very remarkable presentations of colour are seen4 ,under the lower velocities the sky flashes1 and assumes an unnatural brilliancy1 and the intervals of the fourth and fifth of a second give it sometimes a crimson1 at others a deep purple colour4 ,now1 what are we to infer from this experiment8 ,certainly not that the pulsations have absolutely produced variety of colour4 ,at every pulsation the full natural light falls upon the eye1 and the intervals between the pulsations give time for the reaction necessary to the suggestion of complementary colour1 and that under manifold modifications arising out of the ever-changing condition of the eye during the experiment4 ,if the apertures pass the eye with a velocity exceeding one-sixth of a second1 the effect ceases4 ,there is then perfect persistence1 and the eye apprehends nothing but the ordinary light of the sky1 reduced in intensity1 with nothing to break its uniformity or give it a chromatic character4 ,a fourth experiment is kindred to the last4 ,place the kalotrope under the same adjustment and management as before1 in front of a brilliant sunset1 and the spectator will see1 with more than a poet's vision1 ',the rich hues of all glorious things4' ,,xii4 ,the ,kaleidoscopic ,colour-top4 ,this invention by ,john ,graham1 of ,tunbridge1 is designed to show that when white or coloured light is transmitted to the eye through small openings cut into patterns or devices1 and when such openings are made to pass before the eye in rapid successive jerks1 both form and colour are retained upon the nerve of the visual organ sufficiently long to produce a compound pattern1 all the parts of which appear simultaneously1 although presented in succession4 ,the instrument forms1 therefore1 a pleasing illustration of the law that the eye requires an almost inappreciably short space of time to receive an impression1 and that such impression is not directly effaced1 but remains for an assignable though very limited period4 ,the results are obtained by rotating two discs on a wheel1 the lower disc containing colours1 and the upper one the ,page #cai openings2 this latter disc is made to vibrate as well as to rotate1 thus allowing the eye to receive the coloured light reflected from below1 which light assumes1 at the same time1 the forms of the patterns through which it has been transmitted4 ,the instrument serves also to illustrate most of the important phenomena of colour4 ,,xiii4 ,simple ,microscopes and ,telescopes4 ,the ,stanhope lenses are now sold at such a cheap rate1 and are so useful as simple portable microscopes1 that it is hardly worth while to detail any plan by which a cheap single-lens magnifier may be obtained4 ,eloquent vendors of cheap microscopes are to be found in the streets1 who make their instrument of a pill-box perforated with a pin-hole1 in which a globule of glass fixed with ,canada balsam is placed2 and the spherical form of the drop affords the magnifying power3 or a thin platinum wire may be bent into a small circular loop1 and into this may be placed a splinter of flint-glass2 if the flame of a spirit-lamp is urged upon the loop of platinum wire and glass by the blowpipe until it melts1 a small double-convex lens may be obtained1 which will answer very well as a magnifying-glass4 ,practice makes perfect1 and after two or three trials1 a good single lens may be obtained1 which can be mounted between two small pieces of lead1 brass1 or cardboard1 properly fixed together1 with holes through them just large enough to retain the edge of the tiny lens4 ,a prism can be made of two small pieces of window-glass stuck together with a lump of soft beeswax1 and if a few drops of water are placed in the angle1 they are retained by capillary attraction4 ,the prism is used by holding it against a large pin-hole or small slit in a bit of card1 and directing them towards the sky1 when the beautiful colours of the spectrum will be apparent if the card and prism are brought close to the eye4 ,the most simple form of the refracting telescope is made with a lens of any focal length exceeding six inches1 placed at one end of a tin or cardboard tube1 which must be six inches longer than the focal length of the lens2 the tube may be in two parts1 sliding one within the other1 and when the eye is placed at the other end1 an inverted image of the object looked at1 is apparent4 ,by using two double-convex lenses1 a more perfect simple astronomical telescope is obtained4 ,the object-glass1 i4e41 the lens next the object looked at1 must be placed at the end of a tin or pasteboard tube larger than its focus1 and the second lens1 called the eye-glass1 because next the eye1 is a smaller tube1 termed the eye-tube2 and if the focal length of the object-glass is three feet1 the eye-glass must have a one-inch focus1 and of course the eye-tube and glass must slide freely in the tube containing the object-glass4 ,an object-glass of forty feet focus will admit of an eye-glass of only a four-inch focus1 and will1 therefore1 magnify one hundred and twenty times4 ,a tube of forty feet in length would of course be very troublesome to manage1 and therefore it is usual to adopt the plan originally devised by ,huygens1 viz41 that of placing the object-glass in a short tube on the ,page #cbj top of a high pole with a ball-and-socket joint1 whilst the eye-glass is brought into the same line as the object-glass1 and focused with a tube and rack-work properly supported4 ,in an ordinary terrestrial telescope there are four lenses1 in order that the objects seen by its assistance shall not be inverted2 and whenever objects are examined by a common telescope1 they are found to be fringed1 or surrounded with prismatic colours4 ,this disagreeable effect is corrected by the use of achromatic lenses1 in which two kinds of glass are united2 and the light decomposed by one glass1 uniting with the colours produced by the other form white light1 thus a double convex lens of crown glass1 ,c ,c1 may be united with a plano-convex lens of flint glass1 ,f ,f1 which must have a focus about double the length of that of the crown-glass lens4 ,the concave lens corrects the colour or chromatic aberration of the other1 and leaves about one-half of the refracting power of the convex lens as the effective magnifying power of the compound lens4 ,the ,french opticians cement the lenses very neatly together1 and use them in ordinary spy and opera glasses4 7,fig4 #cjg47 ,illustration3 ,fig4 #cjg4 ,a compound achromatic lens1 composed of ,c ,c1 the double-convex lens of crown-glass1 and ,f ,f1 the plano-concave lens of flint-glass4 ,,xiv4 ,the ,stereoscope4 ,this instrument has now attained a popularity quite equal to1 if it does not surpass1 that formerly enjoyed by the kaleidoscope1 and without entering upon the much-vexed question of priority of discovery1 it is sufficient again to mention with the highest respect the names of ,sir ,david ,brewster and ,professor ,wheatstone as identified with the discovery and use of this most pleasing optical instrument4 ,the principle of the stereoscope 7meaning1 solid ,i see7 is copied from nature3 i4e41 when both eyes are employed in the examination of an object1 two separate pictures1 embracing dissimilar forms1 are impressed upon the retin1 and produce the effect of solidity2 if the pictures formed at the back of the eyes could be examined by another person with a stereoscope1 they would come together1 and also produce the effect of solidity4 ,stereoscopic pictures are obtained by exposing sensitized paper in the camera to the picture of an object taken in two positions1 or two cameras are employed to obtain the same result4 ,if the latter mode is adopted1 the stereoscopic pictures must not be taken from positions too widely separated from each other2 or else1 when the two pictures are placed in the stereoscope1 they will stand out with a relief that is quite unnatural1 and the object will appear like a very reduced solid model1 instead of having the natural appearance presented by pictures which have been taken at positions too distant from each other4 ,sir ,david ,brewster says1 ,in order to obtain photographic pictures mathematically exact1 we must construct a binocular camera which will ,page #cba take the pictures simultaneously1 and of the same size2 that is1 by a camera with two lenses of the same aperture and focal length1 placed at the same distance as the two eyes4 ,as it is impossible to grind and polish two lenses1 whether single or achromatic1 of exactly the same focal lengths1 even if we had the very same glass for each1 ,i propose to bisect the lenses1 and construct the instrument with semi-lenses1 which will give us pictures of precisely the same size and definition4 ,these lenses should be placed with their diameters of bisection parallel to one another1 and at a distance of #b inches1 which is the average distance of the eyes in man2 and when fixed in a box of sufficient size1 will form a binocular camera1 which will give us at the same instant1 with the same lights and shadows1 and of the same size1 such dissimilar pictures of statues1 buildings1 landscapes1 and living objects1 as will reproduce them in relief in the stereoscope4 ,thus with a single camera provided with semi-lenses1 or two lenses of the same focal length1 stereoscopic pictures can be obtained4 ,to bring the images of the two pictures together1 and produce the effect of solidity2 either of two instruments may be employed4 ,the reflecting stereoscope is the invention of ,professor ,wheatstone4 ,the refracting or lenticular stereoscope that of ,sir ,david ,brewster4 ,the former is constructed by placing two upright boards on a wooden stand at a moderate distance from each other2 the stereoscopic pictures are attached to these boards1 which may be made to move up or down1 and if the pictures are held in grooves1 they may be pulled right or left at pleasure1 and thus four movements are secured--viz41 upward1 downward1 right1 or left4 ,between the two stereoscopic pictures are placed two looking-glasses1 so adjusted that their backs form an angle of ninety degrees with each other4 7,fig4 #cjh47 ,illustration3 ,fig4 #cjh4 ,wheatstone's reflecting stereoscope4 ,the pictures are illuminated at night by a lamp or gas flame placed at the back of the mirrors1 which1 when fixed together1 have the same shape as a prism2 indeed1 ,professor ,wheatstone substituted a prism for the mirrors1 and thus paved the way for the invention of the lenticular stereoscope4 ,page #cbb ,the stereoscopic effect is obtained by bringing the eyes close to the inclined mirrors1 so that the two reflected images coincide at the intersection of the optic axis2 the coincidence of the images is further secured by moving either picture a little to the right or left1 and if the upright boards move bodily in grooves to or from the centre mirror1 the greatest nicety of adjustment is procured4 ,during the last three years of the author's directorship of the ,polytechnic--viz41 in #ahef1 #aheg1 #aheh--nearly the whole of the pictures shown by the dissolving-view apparatus were coloured photographs from ,mr4 ,hine's original pictures1 painted two feet square in blue and white1 and reduced on the glass to about six inches square4 ,the collodion film being frequently thick and difficult to penetrate with light1 was etched and scratched away where required1 and filled in with colour1 and when these pictures were looked at with one eye only1 they appeared to be almost solid or stereoscopic on the disc4 ,the lenticular stereoscope consists of a box of a pyramidal shape1 open at the base1 and provided with grooves in which are placed the stereoscopic pictures2 if the latter are taken on glass the base of the box is held directly against the light1 but if they are daguerreotypes or paper pictures1 then a side light is reflected upon them by means of a lid covered in the inside with tinfoil1 which is raised or lowered at pleasure from the top part of the box4 ,two semi-lenses are now fitted into the narrow part of the box1 and are placed at such a distance from each other that the centres of the semi-lenses correspond with the pupil of the eyes1 and this distance has already been stated to amount to #b inches4 7,fig4 #cji47 ,illustration3 ,fig4 #cji4 ,brewster's lenticular stereoscope4 ,the principle of the lenticular stereoscope is perhaps better seen by reference to the next diagram1 in which the centres of the semi-lenses 7i4e41 a lens cut in half7 are placed at #b inches apart1 with their thin edges towards each other1 and marked1 ,a ,b1 ,fig4 #caj4 ,the centres of the two stereoscopic pictures ,c ,d correspond with the centres of the lenses1 and the rays of light diverging from ,c ,d fall upon the semi-lenses1 and being refracted nearly parallel are1 by the prismatic form of the semi-lenses1 deflected from their course1 and leave the surfaces of the lenses in the same direction as if they actually emanated from ,e2 and as all images of bodies appear to come in a straight line from the point whence they are seen1 the two pictures are superimposed on each other1 and together produce the appearance of solidity1 so that a stereoscopic result is obtained when the spectral images of the two stereoscopic pictures are made to overlap each other4 ,by taking one of the semi-lenses in each hand1 and looking at the two pictures1 the over-lapping ,page #cbc of the spectral images becomes very apparent1 so that the combined spectral images1 and not the pictures themselves1 are seen when we look into a stereoscope4 7,fig4 #caj47 ,illustration3 ,fig4 #caj4 ,sir ,david ,brewster says1 ,in order that the two images may coalesce without any effort or strain on the part of the eye1 it is necessary that the distance of the similar parts of the two drawings be equal to twice the separation produced by the prism4 ,for this purpose measure the distance at which the semi-lenses give the most distinct view of the stereoscopic pictures1 and having ascertained by using one eye the amount of the refraction produced at that distance1 or the quantity by which the image of one of the pictures is displaced1 place the stereoscopic pictures at a distance equal to twice that quantity--that is1 place the pictures so that the average distance of similar parts in each is equal to twice that quantity4 ,if this is not correctly done1 the eye of the observer will correct the error by making the images coalesce1 without being sensible that it is making any such effort4 ,when the dissimilar stereoscopic pictures are thus united1 the solid will appear standing as it were in relief between the two plane representations4 ,,xv4 ,the ,stereomonoscope4 ,m4 ,claudet1 whose name has long been celebrated in connexion with the art of photography1 has described an instrument by which a single picture is made to simulate the appearance of solidity1 and he states that by means of this arrangement a number of persons may observe the effect at the same time4 ,the apparatus required is very simple1 consisting of a large double convex lens1 and a screen of ground glass4 ,the ,page #cbd object ,a1 ,fig4 #caa1 is highly illuminated1 and placed in the focus of a double convex lens ,b1 when an image of the object is projected1 and will be found suspended in the air in the conjugate focus of the lens at ,c1 and from this point the rays of light will diverge as from a real object1 which will be seen by separate spectators at ,d ,d and ,e ,e2 and if the screen of ground glass is placed at ,g ,g1 the image will appear with all the effect of length1 breadth1 and depth1 which belong to solid bodies4 7,fig4 #caa47 ,illustration3 ,fig4 #caa4 ,the stereomonoscope4 ,an image formed on ground glass in this manner can be seen only in the direction of the incident rays1 and the stereoscopic effect is not apparent when the image is received on a calico or transparent screen1 on account of the rays being scattered in all directions4 ,,xvi4 ,the ,stereomoscope4 ,illustration3 ,fig4 #cab4 ,the stereomoscope4 ,this arrangement is an important modification of the other1 and consists of a screen of ground glass 7,a ,b1 ,fig4 #cab71 and two convex ,page #cbe lenses 7,c ,d1 and ,e ,f7 arranged in such a manner that they will project images of the stereoscopic pictures1 ,g ,h1 at the same point on the screen1 ,a ,b4 ,it might be thought that a confusion of images would result from projecting two pictures on one point1 ,p--viz41 the focus of the two lenses2 but as each photograph can be seen only in the direction of its own rays1 it follows that if the eyes are so placed that each receives the impression of one stereoscopic picture1 the two images must coalesce1 and a stereoscopic effect will be the result1 as is apparent at ,k ,k and ,l ,l2 so that several persons may look at the stereoscope at one time4 7,fig4 #cab47 ,,xvii4 ,the ,pseudoscope4 ,illustration3 ,fig4 #cac4 ,horizontal section of the pseudoscope1 showing at ,a ,b two prisms placed against a block of wood about two inches long and one inch and a half wide1 and cut out in the centre to admit the nose at ,d4 ,the eyes are supposed to be looking at the globe1 ,c1 in the direction of the arrows4 ,e ,e4 ,brass plates blackened1 which shut out the side light1 and assist in keeping the prisms in position4 ,this curious optical instrument1 as its name implies1 produces a false image by the refracting power of prisms1 and is the invention of ,professor ,wheatstone4 ,when used with both eyes1 the same as the stereoscope1 it inverts the relief of a solid body1 and makes it appear exactly as if it were an intaglio1 or sunk beneath the line surrounding it4 ,for instance1 a terrestrial globe when looked at through the pseudoscope appears to be concave1 like ,wyld's ,globe in ,leicester-square1 instead of convex4 ,a vase with raised ornaments upon it looks as if it had been turned 7to reverse the usual expression7 outside in1 and ,page #cbf the whole of its convexity is turned to concavity2 and of course a face seen under these circumstances looks very curious4 7,fig4 #cac47 ,the cause is perhaps somewhat difficult to understand2 but by taking other and more simple examples of the same effect1 the principle may be gradually comprehended4 ,sir ,david ,brewster1 in his ,letters on ,natural ,magic1 remarks that one of the most curious phenomena is that false perception in vision by which we conceive depressions to be elevations1 and elevations depressions--or by which intaglios are converted into cameos1 and cameos into intaglios4 ,this curious fact seems to have been observed at one of the early meetings of the ,royal ,society of ,london1 when one of the members1 in looking at a guinea through a compound microscope of new construction1 was surprised to see the head upon the coin depressed1 while other members could only see it embossed1 as it really was4444 ,the best method of observing this deception is to view the engraved seal of a watch with the eye-piece of an achromatic telescope1 or with a compound microscope1 or any combination of lenses which inverts the objects that are viewed through it2 a single convex lens will answer the purpose1 provided we hold the eye six or eight inches behind the image of the seal formed in its conjugate focus4 ,after bringing forward various interesting experiments in further explanation of the cause1 ,sir ,d4 ,brewster states it to be his belief that the illusion is the result of an operation of our own minds1 whereby we judge of the forms of bodies by the knowledge we have acquired of light and shadow4 ,hence1 the illusion depends on the accuracy and extent of our knowledge on this subject2 and while some persons are under its influence1 others are entirely insensible to it4 ,this statement is borne out by experience1 as the author1 whilst ,resident ,director of the ,polytechnic1 had four of ,wheatstone's pseudoscopes placed in the gallery1 with proper objects behind them2 and he frequently noticed that some visitors would look through the instrument and see no alteration of the convex objects1 whilst others would shout with delight1 and call their friends to witness the strange metamorphosis1 who in their turn might disappoint the caller by being perfectly insensible to its strange effects4 ,the pseudo-effects of vision are not confined to the results already explained1 but are to be observed especially whilst travelling in a coach1 when the eyes may be so fixed as to give the impression of movement to the trees and houses1 whilst the coach appears to stand still4 ,in railway carriages1 after riding for some time and then coming to a stand still1 if another train is set slowly in motion by the one at rest1 it frequently happens that the latter appears to be moving instead of the former4 ,page #cbg ,,chapter ,,xxiv4 ,,the ,,absorption ,,of ,,light4 ,the analysis of light has been explained in a previous chapter1 and it has been shown how the spectrum is produced4 ,colour1 however1 may be obtained by other means1 and the property enjoyed by certain bodies1 of absorbing certain coloured rays in preference to others1 offers another mode of decomposing light4 ,the property of absorption is shown to us in every kind of degree by innumerable natural and artificial substances2 and by examining the spectrum through a wedge of blue glass1 ,sir ,david ,brewster was enabled to separate the seven colours of the spectrum into the three primary colours1 red1 yellow1 and blue1 which he proved existed at every point of the spectrum1 and by over-lapping each other in various proportions1 produce the compound colours of orange1 green1 indigo1 and violet4 ,connected with this property is the remarkable effect produced by coloured light on ordinary colours1 and the sickly hue cast upon the ghost in a melodrama1 or the fiery complexion imparted to the hair of ,der ,freischutz1 or the jaundiced appearance presented by every member of a juvenile assembly when illuminated with a yellow light from the salt and burning spirit of snapdragon1 are too well known to require a lengthened description here4 ,if a number of colours are painted on cardboard1 or groups of plants1 flowers1 flags1 and shawls1 are illuminated by a mono-chromatic light1 and especially the light procured from a large tow torch well supplied with salt and spirit1 the effect is certainly very remarkable2 at the same time it shows how completely substances owe their colour to the light by which they are illuminated1 and it also indicates why ladies cannot choose colours by candle light1 unless of course they propose to wear the dress only at night1 when it is quite prudent to see the colours in a room lit with gas2 and this fact is so well known that with the chief drapers1 such as at ,messrs4 ,halling1 ,pearce1 and ,stone's1 ,waterloo ,house1 a darkened room lit with gas is provided during the daytime to enable purchasers of coloured dresses to judge of the effect of artificial light upon them4 ,whilst the flowers1 c41 are lighted up with the yellow light1 a magical change is brought about by throwing on suddenly the rays from the oxy-hydrogen light1 when the colours are again restored2 or if the latter apparatus is not ready1 the combustion of phosphorus in a jar of oxygen will answer the same purpose4 ,the light obtained from the combustion of gas affords an excess of the yellow or red rays of light1 which causes the difference between candlelight and daylight colours already alluded to4 ,page #cbh ,,chapter ,,xxv4 ,,the ,,inflection ,,or ,,diffraction ,,of ,,light4 ,in this part of the subject it is absolutely necessary to return to the theory of undulations with which the present subject was commenced4 ,the inflection of light offers a third method by which rays of light may be decomposed and colour produced4 ,the phenomena are extremely beautiful1 although the explanation of them is almost too intricate for a popular work of this kind4 ,the cases where colour is produced by inflection are more numerous than might at first be supposed2 thus1 if we look at a gaslight or the setting sun through a wire gauze blind1 protecting the eye with a little tank of dilute ink1 a most beautiful coloured cross is apparent4 ,an extremely thin film of a transparent matter1 such as a little naphtha or varnish dropped on the surface of warm water or soap bubbles1 or a very thin film of glass obtained by blowing out a bulb of red-hot glass till it bursts1 or an exquisitely thin plate of talc or mica1 all present the phenomena of colour1 although they are individually transparent1 and in ordinary thicknesses quite colourless4 ,illustration3 ,fig4 #cad4 ,the two lenses1 with the plate or film of air between them1 and producing seven coloured rings when the lenses are brought sufficiently close to each other by the screws4 ,sir ,isaac ,newton brought his powerful intellect to bear on these facts1 and as a preliminary step invented an instrument for measuring the exact thickness of those transparent substances that afforded colour1 and the apparatus displaying ,newton's rings is still a favourite optical experiment4 ,it consists of a plano-convex lens1 ,a4 7,fig4 #cad71 a slice1 as it were1 from a globe of glass twenty-eight feet in diameter1 or the radius of whose convex surface is fourteen feet4 ,this plano-convex lens is placed on another double convex lens1 ,b41 whose convex surfaces have a radius of fifty feet each1 consequently the lenses are very shallow1 and the space 7,c ,c7 included between them being filled with air1 can of course be accurately measured4 7,fig4 #cad47 ,it is usual to mount the lenses in brass rings which are brought together with screws1 when the most beautiful coloured rings are apparent1 and are produced by the extreme thinness of the film or plate of air enclosed between the two lenses2 and ,page #cbi the relative thicknesses of the plates of air at which each coloured light is reflected are as follows3-- ,red #acc #aj millionths of an inch4 ,orange #abj ,yellow #aac ,green #aje ,blue #ih ,indigo #ib ,violet #hc ,by dividing an inch into ten millions of parts1 and by taking #acc of such parts1 the thickness of the film of air required to reflect the red ray is obtained1 and in like manner the other colours require the minute thicknesses of air recorded in the table above4 ,when the thickness of the film of air is about #ab_/agh1jjj;dths of an inch1 the colours cease to become visible1 owing to the union of all the separate colours forming white light1 but if the ,newton rings are produced in mono-chromatic light1 then a greater number of rings are apparent1 but of one colour only1 and alternating with black rings1 i4e41 a dark and a yellow succeeding each other2 this fact is of great importance as an illustration of the undulatory theory1 and demonstrates the important truth1 that two rays of light may interfere with each other in such a manner as to produce darkness4 ,sir ,david ,brewster remarks that1 ,from his experiments on the colours of thin and of thick plates1 ,newton inferred that they were produced by a singular property of the particles of light1 in virtue of which they possess1 at different joints of their paths1 fits or dispositions to be reflected from or transmitted by transparent bodies4 ,sir ,isaac does not pretend to explain the origin of these fits1 or the cause which produces them1 but terms them fits of transmission and fits of reflexion4 ,sir ,isaac ,newton objected to the theory of undulations because experiments seemed to show that light could not travel through bent tubes1 which it ought to do if propagated by undulations like sound2 and it was reserved for the late ,dr4 ,young to prove that light could and would turn a corner1 in his highly philosophical experiments illustrating the inflection or bending in of the rays of light4 ,dr4 ,young placed before a hole in a shutter a piece of thick paper perforated with a fine needle1 and receiving through it the diverging beams on a paper screen1 found that when a slip of cardboard one-thirtieth of an inch in breadth was held in such a beam of light1 that the shadow of the card was not merely a dark band1 but divided into light and dark parallel bands1 and instead of the centre of the shadow being the darkest part1 it was actually white4 ,dr4 ,young ascertained that if he intercepted the light passing on one side of the slip of card with any opaque body1 and allowed the light to pass freely on the other side of the slip of cardboard1 that all the bands and the white band in the centre disappeared1 and hence he concluded that the bands or fringes within the shadow were produced by the interference ,page #ccj of the rays bent into the shadow by one side of the card1 with the rays bent into the shadow by the other side4 7,fig4 #cae74 ,illustration3 ,fig4 #cae4 ,in order to show how two waves may interfere so as to exalt or destroy each other1 two sets of waves may be propagated on the surface of a still tank or bath of water1 from the two points ,a ,a 7,fig4 #cae71 the black lines or circles representing the tops of the waves4 ,it will be seen that along the lines ,b ,b the waves interfere just half way between each other1 so that in all these directions there will be a smooth surface1 provided each set of waves is produced by precisely the same degree of disturbing force1 so as to be perfectly equal and alike in every respect1 and the first wave of one set exactly half a wave in advance of the first wave of the other1 while at the curve in the direction of all the line ,c ,c1 the waves coincide1 and produce elevations or undulations of double extent2 in the intermediate spaces1 intermediate effects will1 of course1 be produced4 ,professor ,wheatstone has invented some very simple and beautiful acoustic apparatus for the purpose of proving that the same laws of interference exist also in sound1 which1 as already stated1 consists in the vibrations or undulation of the particles of air4 ,page #cca ,the nature and effects of interference are also admirably illustrated by the following models of ,mr4 ,charles ,woodward1 ,president of the ,islington ,scientific ,institution1 and to whom we have already alluded4 ,illustration3 ,fig4 #caf4--,no4 #a4 ,a model of waves with moveable rods4--,no4 #b4 ,a model of fixed waves4--,no4 #c4 ,intensity of waves doubled by the superposition and coincidence of two equal systems4--,no4 #d4 ,waves neutralized by the superposition and interference of two equal systems1 the raised part of one wave accurately fitting into and making smooth the hollow of the other1 illustrating the fact that two waves of light or sound may destroy each other4 ,illustration3 ,fig4 #cag4 ,appearance of ,newton's rings when produced in yellow light1 #a1 #c1 #e1 #g1 being the yellow rings1 and #b1 #d1 #f1 #h1 the dark rings4 ,light by the odd numbers2 darkness by the even numbers4 ,the central spot1 where the two surfaces are in contact1 is dark4 ,returning again to the coloured rings1 we find that ,newton discovered that at whatever thickness of the film of air the coloured ring first appeared1 there would be found at twice that thickness the dark ring1 at three times the coloured1 at four times the dark1 and so on1 the coloured rings regularly occurring at the odd numbers1 and the dark ones at the even numbers4 ,this discovery is well illustrated by the models 7,fig4 #caf72 and it maybe noticed at ,no4 #c that the highest and the lowest parts of the waves ,page #ccb interfere1 but coincide and produce a wave of double intensity2 the little crosses of the upper model are in a straight line with the numbers #a1 #c1 #e1 #g1 and are supposed to represent the coloured rings1 whilst in ,no4 #d the upper series of waves is half an undulation in advance of the lower2 and if the eye is again directed from the little crosses downward1 the figures #b1 #d1 #f1 #h1 even numbers1 are apparent1 and represent the dark rings1 when the waves of light destroy each other4 ,the phenomena of thin plates1 such as colours from soap bubbles1 and the films of varnish1 are well explained by the law of interference4 ,the light reflected from the second surface of the film of air 7which must of course1 however thin1 have two surfaces1 viz41 a upper and a lower one7 interferes with the light reflected from the first1 and as they come from different points of space1 one set of waves is in advance of the other1 ,no4 #d1 ,fig4 #caf2 they reach the eye with different lengths of paths1 and by their interference form alternately the luminous and dark fringes1 bands1 or circles4 ,bridge's diffraction apparatus1 manufactured only by ,elliott ,brothers1 offers itself specially as a most beautiful drawing-room optical instrument4 ,the purpose of this apparatus is to illustrate in great variety1 and in the most convenient and compact form1 the phenomena of the diffraction or interference of light4 ,this is attained by the assistance of photography4 ,transparent apertures in an opaque collodion film are produced on glass1 and a point of light is viewed through the apertures4 ,page #ccc ,the forms of the apertures are exceedingly various1--triangles1 squares1 circles1 ellipses1 parabolas1 hyperbolas1 and combinations of them1 besides many figures of fanciful forms1 are included in the set4 ,when an image of the sun is viewed through these apertures1 figures of extraordinary beauty1 both of form and colour1 are produced2 and of each of these many variations may be obtained by placing the eye-glass of the telescope at different distances from the object glass4 ,many of the figures produced1 especially when the telescope is out of focus1 might suggest very useful hints to those concerned in designing patterns4 ,although the phenomena are chiefly of interest to the student of science1 in consequence of their bearing on theories of light1 yet their beauty and variety render them amusing to all4 ,a few words on the mode of using the apparatus may be of service4 7,fig4 #cah47 ,illustration3 ,fig4 #cah4 ,elliott ,brothers' diffraction apparatus4 ,choose a very bright day1 for then only can the apparatus be used4 ,place the mirror in the sun1 and let the light be reflected on the back of the blackened screen4 ,the lens which is inserted into this screen will then form an exceedingly bright image of the sun4 ,then at the distance of not less than twelve feet1 clamp the telescope to a table in such a position as to view the image thus formed4 ,put the eccentric cap on the end of the telescope1 clean the glass objects carefully1 and attach them to the cap so that they may be turned each in order before the telescope4 ,in this manner1 all those which consist of a series of figures may be viewed4 ,then detach the eccentric cap1 and replace it by the other4 ,into it place any of the single objects4 ,in viewing some of the figures1 brightness is advantageous--in others1 delicacy2 in the former case1 let the lens of long focus be inserted in the screen--in the latter case1 that of shorter focus4 ,in every case1 let the phenomena be observed not only when the telescope is in focus1 but also when the eye-glass is pushed in to various distances4 ,mr4 ,warren de la ,rue has ingeniously taken advantage of the colours produced by thin films of varnish1 and actually fixed the lovely iridescent colour produced in that manner on highly polished paper1 which is termed iridescent paper4 ,a tank of warm water at #hj ,fahr41 about ,page #ccd six inches deep1 and two feet six inches square1 is provided1 and a highly glazed sheet of white or black paper being first wetted on a perforated metallic plate1 is then sunk with the plate below its surface1 care being taken to avoid air bubbles4 ,a peculiar varnish is then allowed to trickle slowly down a sort of tongue of metal placed in the middle of one of the sides of the tank1 and directly the varnish touches the surface of the water it begins to spread out in exquisitely thin films1 and by watching the operation close to a window and skimming away all the imperfect films1 a perfect one is at last obtained1 and at that moment the paper lying on the metal plate is raised from the bottom of the tank1 and the delicate film of varnish secured4 ,when dry1 the iridescent colours are apparent1 and the paper is employed for many ornamental purposes4 ,an extremely simple and pretty method of producing ,newton's rings has been invented by ,reade1 and is called ,reade's iriscope4 ,a plate of glass of any shape 7perhaps circular is the best7 is painted on one side with some quickly drying black paint or varnish1 and after the other side has been cleaned1 it is then rubbed over with a piece of wet soap1 and this is rubbed off with a clean soft duster4 ,a tube of about half an inch in diameter1 and twelve inches long1 is provided1 and is held about one inch above the centre of the soaped side of the glass plate1 and directly the breath is directed down the tube on the glass1 an immense number of minute particles of moisture are deposited on the glass1 and these by inflection decompose the light1 and all the colours of the rainbow are produced4 7,fig4 #cai47 ,illustration3 ,fig4 #cai4 ,reade's iriscope4 ,the iridescent colours seen upon the surface of mother-of-pearl1 which ,mr4 ,simonds' excellent commercial dictionary tells us is the name for the iridescent shell of the pearl oyster1 and other molluscs1 are referrible to fine parallel lines formed by its texture1 and are reproducible1 according to ,brewster's experiments1 by taking impressions of them in soft wax4 ,the gorgeous colours of certain shells and fish1 the feathers of birds1 ,barton's steel buttons1 are not due to any inherent pigment or colouring matter that could be extracted from them1 but are owing either to the peculiar fibrous1 or parallel-lined1 or laminated 7plate-like7 surfaces upon which the light falls1 and being reflected in paths of different lengths1 interference occurs1 and coloured light is produced4 ,page #cce ,,chapter ,,xxvi4 ,,the ,,polarization ,,of ,,light4 ,this branch of the phenomena of light includes some of the most remarkable and gorgeous chromatic effects2 at the same time1 regarded philosophically1 it is certainly a most difficult subject to place in a purely elementary manner before the youthful minds of juvenile philosophers1 and unless the previous chapter on the diffraction of light is carefully examined1 the rationale of the illustrations of polarized light will hardly be appreciated4 ,we have first to ask1 ,what is polarized light8 ,the answer requires us again to carry our thoughts back to the consideration of the undulatory theory of light1 already illustrated and partly explained at pages #bfb1 #ccj4 ,after perusing this portion of the subject1 it might be considered that waves of light were constituted of one motion only1 and that an undulation might be either perpendicular or horizontal1 according to circumstances4 7,fig4 #cbj47 ,illustration3 ,fig4 #cbj4--,no4 #a4 ,a wire bent to represent a perpendicular vibration1 which if kept in the latter position1 will only pass through a perpendicular aperture4--,no4 #b4 ,a wire bent to represent a horizontal wave which will only pass through a horizontal aperture4 ,this simple condition of the waves of light could not1 however1 be reconciled theoretically with the actual facts1 and it is necessary in regarding a ray of light1 to consider it as a combination of two vibrating motions1 one of which1 for the sake of simplicity1 may be considered as perpendicular1 and the other horizontal2 and this idea of the nature of ,page #ccf an undulation of light originated with the late ,dr4 ,young1 who while considering the results of ,sir ,d4 ,brewster's researches on the laws of double refraction1 first proposed the theory of transversal 7cross-wise7 vibration4 ,dr4 ,young illustrated his theory with a stretched cord1 which if agitated or violently shaken perpendicularly1 produces a wave that runs along the cord to the other end1 and may be often seen illustrated on the banks of a river overhung with high bushes2 the bargemen who drive the horses pulling the vessel by a rope1 would be continually stopped by the stunted thick bushes1 but directly they approach them1 they give the horse a lash1 and then violently agitate the rope vertically1 which is thrown into waves that pass along the rope1 and clear the bushes in the most perfect manner4 7,fig4 #cba47 ,illustration3 ,fig4 #cba4 ,bargeman throwing his tow-rope into waves to get it over the thick bushes4 ,illustration3 ,fig4 #cbb4 ,a section of a wave of common light made up of the transversal vibration1 ,a ,b and ,c ,d4 ,now if a similar movement is made with the stretched rope from right to left1 another wave will be produced1 which will run along the cord in an horizontal position1 and if the latter is compared with the perpendicular undulation1 it will be evident that each set of waves will be in planes at right angles to and independent of each other4 ,this is supposed to be the mechanism of a wave of common light1 so that if a section is taken of such an undulation1 it will be represented by a circle ,a ,b ,c ,d 7,fig4 #cbb71 with two diameters ,a ,b1 and ,c ,d2 or a better mechanical notion of a wave of common ,page #ccg light is acquired from the inspection of another of ,mr4 ,woodward's cardboard models4 7,fig4 #cbc47 ,illustration3 ,fig4 #cbc4 ,model of a wave of common light4 ,the existence of an alternating motion of some kind at minute intervals along a ray is1 says ,professor ,baden ,powell1 as real as the motion of translation by which light is propagated through space4 ,both must essentially be combined in any correct conception we form of light4 ,that this alternating motion must have reference to certain directions transverse to that of the ray is equally established as a consequence of the phenomena2 and these two principles must form the basis of any explanation which can be attempted4 ,a beam of common light is therefore to be regarded as a rapid succession of systems of waves in which the vibrations take place in different planes4 ,if the two systems of waves are separated the one from the other1 viz41 the horizontal from the perpendicular1 they each form separately a ray of polarized light1 and as ,fresnel has remarked1 common light is merely polarized light1 having two planes of polarization at right angles to each other4 ,to follow up the mechanical notion of the nature of polarized light1 it is necessary to refer again to ,woodward's card wave model 7,fig4 #cbc71 and by separating the two cards one from the other it may be demonstrated how a wave of common light reduced to its skeleton or primary form is reducible into two waves of polarized light1 or how the two cards placed together again in a transversal position form a ray of common light4 7,fig4 #cbd47 ,illustration3 ,fig4 #cbd4--,no4 #a4 ,common light1 made up of the two waves of polarized light1 ,nos4 #b and #c4 ,the query with respect to the nature of polarized light being answered1 it is necessary1 in the next place1 to consider how the separation of these transversal vibrations may be effected1 and in fact to ask what optical arrangements are necessary to procure a beam of polarized light8 ,light may be polarized in four different ways--viz41 by reflection1 single refraction1 double refraction1 and by the tourmaline--viz41 by absorption4 ,page #cch ,polarization by ,reflection1 and by ,single ,refraction4 ,illustration3 ,fig4 #cbe4--,no4 #a4 ,a is the lime light4 ,b4 ,the condenser lenses4 ,c4 ,the beam of common light4 ,here the glass plates are removed4--,no4 #b4 ,a4 ,lime light4 ,b4 ,the condenser lenses4 ,c ,c4 ,the bundle of plates of glass at an angle of #ef #de4 ,d is the ray of light polarized by reflection from the glass plates1 ,c ,c1 and ,e is the beam of polarized light by single refraction1 having passed through the bundle of plates of glass1 ,c ,c4 ,in the year #ahaj1 the celebrated ,french philosopher1 ,mons4 ,malus1 while looking through a prism of ,iceland spar1 at the light of the setting sun1 reflected from the windows of the ,luxemburg palace in ,paris1 discovered that a beam of light reflected from a plate of glass at an angle of #ef degrees1 presented precisely the same properties as one of the rays formed by a rhomb of ,iceland spar1 and that it was in fact polarized4 ,one of the transversal waves of polarized light of the common light1 being reflected or thrown off from the surface of the glass1 whilst the other and second transversal vibration passed through the plate of glass1 and was likewise polarized in another plane1 but by single refraction1 so that the experiment illustrates two of the modes of polarizing light-viz41 by reflection1 and by single refraction4 ,this important elementary truth is beautifully illustrated by ,mr4 ,j4 ,t4 ,goddard's new form of the oxy-hydrogen polariscope1 by which a beam of common light traverses a long square tin box without change2 but directly a bundle of plates of glass composed of ten plates of thin flattened crown glass1 or sixteen plates of thin parallel glass plates used for microscopes1 are slid into the box at an angle of #ef #de1 then the beam of common ,page #cci light is split into two beams of polarized light1 which pursue their respective paths1 one passing by single refraction through the glass1 and the other being reflected1 and rendered apparent by opening an aperture over the glass plates1 and then again by using a little smoke from brown paper1 the course of the rays becomes more apparent4 ,illustration3 ,fig4 #cbf4 ,a ,a4 ,model in wood of a bundle of plates of glass at an angle of #ef #de4 ,b4 ,beam of common light1 with transversal vibration4 ,c4 ,light polarized by reflection4 ,d4 ,light polarized by refraction4 ,the same truth is well illustrated by the cardboard model wave and a wooden plane with horizontal and perpendicular slits1 placed at an angle of #ef #de1 as at ,fig4 #cbf4 ,,polarization ,,by ,,double ,,refraction4 ,the name of ,double-refracting or ,iceland ,spar is given to a very clear1 limpid1 and perfectly transparent mineral1 composed of carbonate of lime1 and found on the eastern coast of ,iceland4 ,its crystallographic features are well described by the ,rev4 ,walter ,mitchell in his learned work on mineralogy and crystallography1 and it is sufficient for the object of this article to state that it crystallizes in rhombs1 and modifications of the rhomboidal system4 ,it must not be confounded with rock or mountain crystal1 which1 under the name of quartz1 crystallizes in six-sided prisms with six-sided pyramidal tops2 quartz being composed of silica1 or silicic acid and calcareous spar of carbonate of lime4 ,very large specimens of the latter mineral are rare and valuable1 and the lion of specimens of calcareous1 or double-refracting spar1 is now in the possession of ,professor ,tennant1 the eminent mineralogist of the ,strand4 ,it is nine inches high1 seven and three-quarters inches broad1 and five and a half inches thick2 its estimated value being #ajjl4 ,this beautiful specimen has been photographed1 and its stereograph illustrates in a very striking manner the double refracting properties of the spar4 ,if a printed slip of paper is placed behind a rhomb of ,iceland spar1 two images of the former are apparent1 and the stereograph already alluded to shows this fact very perfectly1 at the same time illustrates the value of the stereoscope4 ,out of the stereoscope the words ,stereoscopic ,magazine appear doubled1 but seem to lie in the same plane2 but directly the picture is placed in the instrument1 then it is clearly seen that one image is evidently in a very different plane from the other4 ,the double-refracting power of this mineral is illustrated by holding a small rhomb of ,iceland spar1 placed in a proper brass tube before the orifice as at ,fig4 #cbg1 from which the rays of common light are ,page #cdj passing2 if an opaque screen of brass perforated with a small hole is introduced behind the rhomb1 then1 instead of one circle of light being apparent on the screen1 two are produced1 and both the rays issuing in this manner are polarized1 one being termed the ordinary and the other the extraordinary ray4 7,fig4 #cbg47 ,illustration3 ,fig4 #cbg4 ,a4 ,the condensers4 ,b4 ,the hole in the brass screen or stop4 ,c4 ,the rhomb of ,iceland spar4 ,o4 ,the ordinary1 and ,e the extraordinary1 ray1 both of which are polarized light4 ,the polarizing property of the rhomb is perhaps better shown by the next diagram1 where ,a ,b represents the obtuse angles of the ,iceland spar1 and a line drawn from ,a to ,b1 would be the axis of the crystal4 ,the incidental ray of common light is shown at ,c1 and the oppositely polarized transmitted rays called the ordinary ray ,o1 and extraordinary ray ,e1 emerge from the opposite face of the rhomboid4 ,if a black line is ruled on a sheet of paper as at ,k ,k1 and examined by the eye at ,c1 it appears double as at ,k ,k and ,j ,j4 7,fig4 #cbh47 ,illustration3 ,fig4 #cbh4 ,rhomb of ,iceland spar4 ,the cardboard model is again useful in demonstrating the polarization of light by double refraction1 and if a model of a rhomb of ,iceland ,page #cda spar is made of glass plates1 one face of which has an aperture like a cross1 and the other a horizontal and perpendicular slit1 as at ,nos4 #a and #b 7,fig4 #cbi71 the production of the ordinary and extraordinary rays is demonstrated in a familiar manner1 and is easily comprehended4 ,illustration3 ,fig4 #cbi4--,no4 #a4 ,one face of the model rhomb to admit the transversal vibration1 represented by the cardboard model4--,no4 #b4 ,the opposite face of the rhomb1 from which issue the polarized1 ordinary1 and extraordinary rays4--,no4 #c4 ,side view of the model4 ,in ,newton's ,optics we find the following description of ,iceland spar3--,this crystal is a pellucid fissile stone1 clear as water or crystal of the rock 7quartz71 and without colour4444 ,being rubbed on cloth it attracts pieces of straw and other light things like amber or glass1 and with aquafortis it makes an ebullition4444 ,if a piece of this crystalline stone be laid upon a book1 every letter of the book seen through it will appear double by means of a double refraction4 ,,polarization ,,by ,,the ,,tourmaline4 ,this mineral was first discovered during the sixteenth century1 in the island of ,ceylon1 afterwards in ,brazil1 and since that period at various localities in the four quarters of the globe4 ,in the ,grevillian collection purchased many years ago by government for the ,british ,museum1 there is a fine specimen of red tourmaline valued at #ejjl4 ,the green tourmaline is named ,brazilian emerald1 and the ,berlin blue tourmaline is called ,brazilian sapphire2 the mineral chiefly consists of sand 7silica7 and alumina1 with a small quantity of lime1 or potash1 or soda1 boracic acid1 and sometimes oxide of iron or manganese4 ,when light is passed through a slice of this mineral it is immediately polarized1 one of the transversal vibrations being absorbed1 stopped1 or otherwise disposed of1 the other only emerging from the tourmaline1 consequently it is one of the most convenient polarizers1 although the polarized light partakes of the accidental colour of the mineral4 ,green1 blue1 and yellow tourmalines are bad polarizers1 but the brown and pink varieties ,page #cdb are very good1 and it is a most curious fact that white tourmaline does not polarize4 7,fig4 #ccj47 ,illustration3 ,fig4 #ccj4 ,crystal of tourmaline slit 7parallel to the axis7 into four plates1 which when ground and polished1 may be used for the polarization of light4 ,the mineral crystallizes in long prisms1 whose primitive form is the obtuse rhomboid1 having the axis parallel to the axis of the prism4 ,the term axis with reference to the earth1 as shown at page #af1 is an imaginary single line around which the mass rotates1 but in a crystal it means a single direction1 because a crystal is made up of a number of similar crystals1 each of which must have its axis1 thus the whitest ,carrara marble reduced to fine powder1 moistened with water and placed under a microscope1 is found to consist chiefly of minute rhomboids1 similar to calcareous spar4 ,the smallest crystal of this mineral is divisible again and without limit into other rhombs1 each of which possesses an axis4 7,fig4 #cca47 ,illustration3 ,fig4 #cca represents a crystal1 the axis of which is the direction ,a ,b4 ,the dotted lines show the division of the large crystal into four other and smaller ones1 each of which has its axis1 ,a ,c1 ,c ,b1 ,d ,e1 ,f ,g2 and every line within the large crystal parallel to ,a ,b is an axis1 consequently the term is employed usually in the plural number axes4 ,if a plate of tourmaline is held before the eye whilst looking at the sun 7like the gay youth in ,hogarth's picture who is being arrested whilst absorbed with the wonders of a tourmaline1 which was1 in the great painter's time1 a popular curiosity17 it may be turned round in all directions without the slightest difference in the appearance of the light1 which will be coloured by the accidental tint of the crystal1 but if a second slice of tourmaline is placed behind the other1 there will be found certain directions in which the light passes through both the slices1 whilst in other positions the light is completely cut off4 ,page #cdc ,when the axes of both plates coincide1 the light polarized by one tourmaline will pass through the other1 but if the axes do not coincide1 and are at right angles to each other1 then the polarized light is entirely stopped1 and the rationale of this will be appreciated at once if a tourmaline is regarded 7mechanically7 as if it were like a grating with perpendicular bars through which the polarized light will pass4 ,any number of such gratings with the bars parallel would not stop the polarized light1 but if the second grating is turned round ninety degrees1 the bars will be at right angles to those of the first grating1 and the perpendicular wave of polarized light cannot pass4 7,fig4 #ccb47 ,illustration3 ,fig4 #ccb4 ,a4 ,model of the first slice of tourmaline into which the transversal vibrations1 ,b1 are passing2 the horizontal wave is absorbed1 and the perpendicular polarized one proceeds to the second slice of tourmaline1 ,c1 where the bars 7the axes7 being at right angles to those of ,a1 it is stopped1 and cannot pass through until the bars of ,c are parallel with ,a4 ,splendid ,chromatic effects produced by ,polarized ,light4 ,having discussed the various modes of obtaining polarized light1 the next step is to arrange an apparatus by which certain double refracting crystals1 and other bodies1 shall divide a ray of polarized light1 and then by subsequent treatment with another polarizing surface1 the divided rays are caused to interfere with each other1 and afford the phenomena of colour4 ,bodies that refract light singly1 such as gases1 vapours or liquids1 annealed glass1 jelly1 gums1 resins1 crystallized bodies of the tessular system1 such as the cube and octohedron1 do not afford any of the results which will be explained presently1 except by the influence of pressure1 as in unannealed glass1 or a bent cold glass bar4 ,by compression or dilatation1 they are changed to double refractors of light4 ,the bodies that possess the property of double refraction 7though not to the visible extent of ,iceland spar71 are all other bodies such as crystallized chemicals1 salts1 crystallized minerals1 animal and vegetable substances possessing a uniform structure1 such as horn and quill2 all these substances divide the ray of polarized light into two parts1 and by placing a thin film of a crystal of selenite 7which is one of the best minerals that can be used for the purpose7 in the path of the beam of polarized light1 coming either from the glass plates1 as in ,no4 #b1 7,fig4 #cbe71 page #cch1 or from a slice of tourmaline1 and then receiving it through the ordinary focusing lenses or object-glasses of the oxy-hydrogen microscope1 no colour is yet apparent in the image of the selenite on the screen1 until ,page #cdd another tourmaline1 or a bundle of glass plates1 is placed at an angle of #ef #de1 and at right angles to the plane of reflection of the first set of plates2 then the most gorgeous colours suddenly appear over all parts of the film of selenite as depicted on the screen1 like other objects shown by the oxy-hydrogen microscope4 7,fig4 #ccc47 ,illustration3 ,fig4 #ccc4 ,duboscq's polarizing apparatus1 ,a4 ,the light and the condenser lens4 ,b4 ,the plates of glass at the proper angle1 ,c4 ,the selenite object1 ,d4 ,the focusing lens4 ,e4 ,the second bundle of plates of glass called the analyser1 ,f4 ,a stop for extraneous rays of light1 ,g4 ,the image of the film of selenite most beautifully coloured4 ,goddard's oxy-hydrogen polariscope is one of the most convenient1 because either the reflected or refracted polarized rays can be rendered available2 it consists of the apparatus shown at ,fig4 #cbe1 and to this is added a low microscope power1 and stage to hold the selenite or other objects1 with another bundle of sixteen plates of the thin microscopic glass or mica1 called the analyser4 ,a slice of tourmaline1 or a ,nicol's prism may be employed1 instead of the second bundle of reflecting plates4 ,when the ray of polarized light reflected from the first set of glass plates enters the doubly refracting film of selenite1 which is about the fortieth or fiftieth part of an inch in thickness1 it is split into the ordinary and extraordinary rays1 and is said to be dipolarized1 and forms two planes of polarized light1 vibrating at right angles to each other4 ,when the latter are received on another bundle of plates of glass called the analyser1 at an angle of #ef #de1 but at right angles to the first set of glass plates1 they interfere1 because in the passage of the two rays from the selenite they have traversed it in different directions1 with different velocities2 one of these sets of waves will therefore1 on emerging from the opposite face of the selenite be retarded1 and lie ,page #cde behind the other2 but being polarized in different planes1 they cannot interfere until their planes of polarization are made to coincide1 which is ,page #cdf effected by means of the second bundle of glass plates called the analyser2 and when this is brought into a position at right angles to the first set of reflecting glass plates1 half the ordinary wave interferes with half the extraordinary wave2 and being transmitted through the analyser1 produces1 say red and orange1 whilst the remaining halves also interfere1 and being reflected1 afford the complementary colours green and blue4 7,fig4 #ccd47 ,the term complementary is intended to define any two colours containing red1 yellow1 and blue1 because the three combined together produce white light2 for example1 the complementary colour to red would be green1 because the latter contains yellow and blue2 the complementary colour to orange would be blue1 because the former contains red and yellow4 ,any two colours1 therefore1 which together contain red1 yellow1 and blue are said to be complementary2 and if this principle was better understood1 ladies would never commit such egregious blunders as they occasionally do in the choice of colours for bonnets and dresses1 and select a blue bonnet to be worn with a green dress1 or vice vers4 ,by rotating the analyser1 the reflected and refracted rays change colours1 and if the former is red and the latter green1 by moving the analyser round #ij1 the reflected rays change to green and the refracted to red2 at #ahj the colours again change places2 at #bgj the reflected ray will be again green1 and the refracted red2 to be once more brought back at #cfj to the original position1 viz41 reflected rays red1 refracted green4 ,the thickness of the films of selenite determines the particular colour produced4 ,illustration3 ,fig4 #ccd4 ,the electric lamp and lantern of ,duboscq1 showing the projection of the carbon poles on the disc4 ,this experiment is performed with the help of the plano-convex lens1 ,a1 and the rays pass through a very narrow aperture at ,b4 ,illustration3 ,fig4 #cce4 ,a ,a4 ,card model of a beam of polarized light coming from the first bundle of plates of glass1 shown at ,fig4 #cbf1 p4 #cci4 ,b4 ,model of the film of selenite1 which divides or dipolarizes the ray ,a ,a into ,c and ,d1 which1 interfering by means of the second bundle of plates of glass called the analyser ,z1 produce reflected chromatic effects by interference at ,e1 and refracted effects at ,f4 ,if the selenite is of a uniform thickness1 one colour only is obtained1 and by ingeniously connecting pieces of various thicknesses 7in the same forms as stained glass for cathedral windows71 the most beautiful designs were made by the late ,mr4 ,j4 ,t4 ,cooper1 jun41 which have since been manufactured in great quantity and variety by ,mr4 ,darker1 of ,paradise-street1 ,lambeth4 ,the colours of these selenite objects are seen by placing them in front of a piece of black glass1 fixed at the polarizing angle1 and then examining the design with a slice of tourmaline1 or still better with a single-image ,nicol prism1 when the most brilliant colours are obtained1 and varied at every change of the angle of the analyser4 ,selenite1 or sparry-gypsum1 is the native crystallized sulphate of lime1 which contains water of crystallization 7,ca,o1 ,,so#c1 #b;,h#b,o74 ,it frequently occurs imbedded in ,london clay1 and is called quarry glass by the labourers who find it at ,shotover ,hill1 near ,oxford1 and also in the ,isle of ,sheppey4 ,at a very early period1 before the discovery of glass1 selenite was used for windows2 and we are told that in the time of ,seneca1 it was imported into ,rome from ,spain1 ,cyprus1 ,cappadocia1 and even from ,africa4 ,it continued to be used for this purpose until the middle ages1 for ,albinus informs us1 that in his time1 the windows of the dome of ,merseburg were of this mineral4 ,the first greenhouses1 those invented by ,tiberius1 were covered with selenite4 ,according to ,pliny1 beehives were encased in selenite1 in order that the bees might be seen at work4 ,page #cdg ,the late ,dr4 ,pereira has placed the phenomena already described in the form of a most instructive diagram1 which we borrow from his elaborate work on ,polarized ,light4 7,fig4 #ccf47 ,illustration3 ,fig4 #ccf4 ,a4 ,a ray of common or unpolarized light1 incident on ,b4 ,b4 ,the polarizer 7a plate of tourmaline74 ,c4 ,a ray of plane polarized light1 incident on ,d4 ,d4 ,the doubly-refracting film of selenite4 ,e4 ,the extraordinary ray4 ,o4 ,the ordinary ray1 produced by the double refraction of the ray ,c4 ,g4 ,the analyser 7or doubly-refracting or ,nicol's prism74 ,e ,o4 ,the ordinary ray4 ,e ,e4 ,the extraordinary ray1 produced by the double refraction of the extraordinary ray1 ,e4 ,o ,o4 ,the ordinary ray4 ,o ,e4 ,the extraordinary ray1 produced by the double refraction of the ordinary ray1 ,o4 ,illustration3 ,fig4 #ccg4 ,no4 #a4 ,unannealed glass for the polariscope4 ,nos4 #b and #c4 ,appearance of the black cross and coloured circles in a square and circular piece of unannealed glass in the polariscope4 ,the chromatic effects described are not confined to selenite objects only1 but are obtained from glass1 provided the particles are in a state of unequal tension1 as in masses of unannealed glass of various forms4 7,fig4 #ccg47 ,consequently1 polarized light becomes a most valuable means for ascertaining the condition of particles otherwise invisible and inappreciable4 ,one of the most beautiful experiments can be made ,page #cdh with a bar of plate-glass1 which refracts light singly until pressure is applied to the centre1 in order to bend it into an arch or curve1 when the appearance presented in ,fig4 #cch is apparent4 ,illustration3 ,fig4 #cch4 ,a ,b4 ,bar of glass under the pressure of the screw ,c1 and appearance of bands or fringes of coloured light1 which entirely disappear on the removal of the screw4 ,an effect1 of course1 only visible by polarized light4 ,a quill placed in the polarizing apparatus is also discovered to be in a state of unequal tension by the appearance of coloured fringes within it1 which change colour at every movement of the analyser4 ,another series of beautiful appearances present themselves when a ray of white polarized light is made to pass perpendicularly through a slice of any crystallized substance with a single axis2 if the analyser consist of a slice of tourmaline1 a number of concentric coloured rings are rendered visible with a black cross in the centre1 which is replaced with a white one on moving the tourmaline through each quadrant of the circle4 ,crystals of ,iceland spar present this phenomenon in great beauty2 and if the crystal 7such as nitre7 has two axes of double-refraction1 a double-system of coloured rings is apparent1 with the most curious changes and combinations of the black and white crosses with them4 7,fig4 #cci47 ,illustration3 ,fig4 #cci4 ,crystal of nitre with two axes1 as seen in polarized light4 ,mr4 ,goddard has recommended the optical arrangement 7,fig4 #cdj7 for showing the rings with great perfection1 as also the number of rings that increase in some crystals 7the topaz1 for example71 with the divergence of the rays of polarized light passing through them4 ,mr4 ,woodward's table and oxy-hydrogen polariscope and microscope1 made by ,smith and ,beck1 of ,coleman-street1 is well adapted1 from its ,page #cdi simplicity and perfection1 to exhibit all the varied and beautiful effects of polarized light2 and we only regret that want of space prevents us describing it in detail1 although the reader may see the body of the apparatus at page #abc1 where the modifications of the oxy-hydrogen light are described and figured2 and the polarizing apparatus would be placed1 of course1 in front of the light issuing from the lantern4 ,illustration3 ,fig4 #cdj4 ,a ,a ,a4 ,polarized light4 ,b ,b4 ,a lens of short focus1 transmitting a cone of light with an angle of divergence for its rays1 ,c ,c1 of #de4 ,d ,d4 ,the crystal of topaz1 ,iceland spar1 or nitre4 ,e ,e4 ,the slice of blue tourmaline for analysing4 ,finally1 the question of utility 7the cui bono7 may be considered in answer to the query1 ,what is the use of polarized light8 ,the value to scientific men of a knowledge of the nature of this modification of common light cannot be overrated4 ,it has given the philosopher a new kind of test1 by which he discovers the structure of things that would otherwise be perfectly unknown2 it has given the astronomer increased data for the exercise of his reasoning powers2 whilst to the microscopist the beauty of objects displayed by polarized light has long been a theme of admiration and delight1 and has served as a guide for the identification of certain varieties of any given substance1 such as starch4 ,a tube provided with a polarizer of tourmaline1 or a single-image ,nicol prism1 is invaluable to the look-out at the mast-head in cases where vessels are navigating either inland or sea water1 where the presence of hidden rocks is suspected1 because the polarizer rejects all the glare of light arising from unequal reflection at the surface of water1 and enables the observer to gaze into the depths of the sea and to examine the rocks1 which can only be perfectly visible by the refracted light coming from their surfaces through the water4 ,professor ,wheatstone has invented an ingenious polarizing clock for showing the hour of the day by the polarizing power of the atmosphere4 ,birt1 ,powell1 and ,leeson have each invented instruments for examining the circular polarization of fluids1 by which a more intimate knowledge of the relative values of saccharine solutions may be obtained1 besides unfolding other truths important to investigators in this branch of science4 ,and last1 but not least1 it was with the assistance of polarized light ,page #cej that ,dr4 ,faraday established the relation that exists between light and magnetism1 and through the latter1 with the force of electricity2 and the next figure indicates the necessary apparatus required to repeat this highly important physical truth--viz41 the deviation of the plane of polarization of light by the influence of the magnetic force from a powerful electro-magnet4 7,fig4 #cda47 ,illustration3 ,fig4 #cda4 ,a4 ,the light and condenser lens4 ,b4 ,single-image ,nicol prism4 ,c4 ,rock crystal of two rotations4 ,d4 ,a double-convex lens4 ,e ,e4 ,faraday's heavy glass4 ,f ,f4 ,the powerful electro-magnet connected with battery4 ,g4 ,double-refracting prisms4 ,h4 ,image1 or screen where the deviation of the plane of polarization by the magnetic force is shown4 ,by another and equally beautiful experiment at the ,london ,institution1 ,professor ,grove demonstrated the production of all the other kinds of force from light1 using the following arrangement for the purpose3 ,a prepared daguerrotype plate is enclosed in a box full of water having a glass front with a shutter over it2 between this glass and the plate is a gridiron of silver wire2 the plate is connected with one extremity of a galvanometer coil1 and the gridiron of wire with one extremity of a ,breguet's helix2 the other extremities of the galvanometer and helix are connected by a wire1 and the needles brought to zero4 ,as soon as a beam of either daylight or the oxy-hydrogen light is1 by raising the shutter1 permitted to impinge upon the plate1 the needles are deflected4 ,thus1 light being the initiatory force1 we get ,chemical action on the plate1 ,electricity circulating through the wires1 ,magnetism in the coil1 ,heat in the helix1 ,motion in the needle4 ,such1 then1 are some of the glorious phenomena that we have endeavoured to explain in this and the preceding chapters on light4 ,here we have noticed specially how completely we owe their appreciation to the sense of sight operating through the eye1 the organ of vision4 ,well may those who have lost this divine gift speak of their darkness as of a lost world of beauty to be irradiated only by better ,page #cea and more enduring light2 and most feelingly does ,sir ,j4 ,coleridge speak on this point when he says3-- ,conceive to yourselves1 for a moment1 what is the ordinary entertainment and conversation that passes around any one of your family tables2 how many things we talk of as matters of course1 as to the understanding and as to the bare conception of which sight is absolutely necessary4 ,consider1 again1 what an affliction the loss of sight must be1 and that when we talk of the golden sun1 the bright stars1 the beautiful flowers1 the blush of spring1 the glow of summer1 and the ripening fruit of autumn1 we are talking of things of which we do not convey to the minds of these poor creatures who are born blind1 anything like an adequate conception4 ,there was once a great man1 as we all know1 in this country1 a poet--and nearly the greatest poet that ,england has ever had to boast of--who was blind2 and there is a passage in his works which is so true and touching that it exactly describes that which ,i have endeavoured1 in feeble language1 to paint4 ,milton says3-- ',thus with the year ,seasons return2 but not to me returns ,day1 or the sweet approach of even1 or morn1 ,or sight of vernal bloom1 or summer's rose1 ,or flocks1 or herds1 or human face divine2 ,but cloud instead1 and ever-during dark ,surrounds me2 from the cheerful ways of men ,cut off1 and for the book of knowledge fair ,presented with a universal blank ,of ,nature's works1 to me expunged and rased1 ,and wisdom at one entrance quite shut out4 ,so much the rather1 thou1 celestial light1 ,shine inward1 and the mind through all her powers ,irradiate2 there plant eyes2 all mist from thence ,purge and disperse1 that ,i may see and tell ,of things invisible to mortal sight4' ,the great poet1 when intent upon his work1 sought for celestial light to accomplish it4 ,and this brings me to that part of the labours of our ,blind ,institutions upon which ,i dwell the most and which1 after all1 is the greatest compensation we can afford to the inmates for the affliction they suffer2 and that is1 the means we provide for them to read the blessed ,word of ,god1 which they can read by day as well as by night1 for light in their case is not an essential4 ,illustration ,page #ceb ,,chapter ,,xxvii4 ,,heat4 ,illustration3 ,fig4 #cdb4 ,james ,watt4 ,throughout the greater number of the preceding chapters it will be evident that the active properties of matter may be summed up under one general head1 and may be considered as varieties of attraction--such as the attraction of gravitation1 cohesive attraction1 adhesive attraction1 attraction of composition 7or chemical attraction71 electrical attraction1 magnetical attraction4 ,the absolute or autocratic system does not1 however1 prevail in the works of nature2 and she seems ever anxious1 whilst imparting great and peculiar powers to certain agents1 to create other forces which may control and balance them4 ,thus1 for instance1 the great force of cohesive attraction is an ever-present power discernible1 as has been shown1 in solids and liquids2 but if this agent ,page #ceb were allowed to run riot in its full strength and intensity1 it would tyrannically hold in subjection all liquid matter1 and every drop of water which is at present kept in the liquid state1 would succumb to its iron rule1 and retain the solid state of ice4 ,hence1 therefore1 the wise creation of an antagonistic force--viz41 heat2 which is not provided in any niggardly manner1 but is liberally bestowed upon the globe from that all-sufficient and enormous source1 the sun4 ,and it is by the softening and liquifying influence of his rays that the greater proportion of the water on the surface of the globe is maintained in the fluid condition1 and is enabled to resist the power of cohesion1 that would otherwise turn it all1 as it were1 to stone4 ,cohesion1 electricity1 and magnetism fully embody the notion of powers of attraction1 or a drawing together2 whilst heat stands almost alone in nature as the type of repulsion1 or a driving back4 ,mechanically1 repulsion is demonstrated by the rebound of a ball from the ground2 the parts which touch the earth are for the moment compressed1 and it is the subsequent repulsion between the particles in those parts which causes them to expand again and throw off the ball4 ,the development of heat is produced from various causes1 which may be regarded as at least four in number4 ,thus1 it was shown by ,sir ,humphrey ,davy1 that even when two lumps of ice are rubbed together1 sufficient heat is obtained to melt the two surfaces which are in contact with each other4 ,friction is therefore an important source of heat1 and one of the most interesting machines at the ,paris ,exposition consisted of an apparatus by which many gallons of water were kept in the boiling state by means of the heat obtained from the friction of two copper discs against each other4 ,the machine attracted a good deal of attention on its own merits1 and especially because it supplied boiling water for the preparation of chocolate1 which the public was duly informed was boiled by the heat rubbed out of the otherwise cold discs of copper4 ,when cannon made on the old system are bored with a drill1 it is necessary that the latter should be kept quite cool with a constant supply of water1 or else the hard steel might become red-hot1 and would then lose its temper1 and be no longer capable of performing its duty4 ,count ,rumford endeavoured to ascertain how much heat was actually generated by friction4 ,when a blunt steel bore1 three inches and a half in diameter1 was driven against the bottom of a brass cannon seven inches and a half in diameter1 with a pressure which was equal to the weight of ten thousand pounds1 and made to revolve thirty-two times in a minute1 in forty-one minutes #hcg grains of dust were produced1 and the heat generated was sufficient to raise #aac pounds of the metal #gj ,fahrenheit--a quantity of heat which is capable of melting six pounds and a half of ice1 or of raising five pounds of water from the freezing to the boiling point4 ,when the experiment was repeated under water1 two gallons and a half of water1 at #fj ,fah41 were made to boil in two hours and a half4 ,chemical affinity has been so often alluded to in these pages1 that it ,page #ced may be sufficient to mention only one good instance of its almost magical power in evoking heat4 ,when a bit of the metal sodium is placed on the tip of a knife1 and thrust into some warm quicksilver1 or if a pellet of sodium and a few globules of mercury are placed on a hot plate just taken from the oven1 and then gently squeezed together1 a vivid production of heat and light is apparent2 and when the mixture of the two metals is cold1 it will be found that the quicksilver has lost its fluidity1 and a solid amalgam of sodium and mercury is obtained1 which gradually1 by exposure to the air1 returns to the liquid state1 the mercury being set free1 whilst the sodium is oxidized1 and forms soda4 ,just as an ordinary alloy of copper and gold used by jewellers would lose its colour and brilliancy by the oxidation of the copper2 and when the rusty1 dirty film is removed by rubbing and polishing1 the surface is again brilliant1 and remains so until another film of the exposed copper is attacked3 in like manner the sodium is attacked and changed by the oxygen of the air1 whilst the mercury being unaffected retains its brilliancy1 and at the same time regains its fluidity4 ,the evolution of heat in the above case indicates that a chemical union has taken place between the two metals4 ,examples of the production of heat by electricity and magnetism have been abundantly shown in the chapters on these subjects2 and one of the best illustrations of this fact has been shown on the occasion of the opening of the telegraphic communication between ,france and ,england by means of the submarine cable1 when cannon were fired alternately at both ends of the conducting cable by means of electricity1 and the event thus inaugurated in both countries4 ,that heat is a product of living animal organization is shown1 as it were1 visibly by the marvellous phenomena that proceed in our own bodies4 ,people do not very often trouble themselves to ask where the heat comes from1 or even to think that this invisible power must be maintained in the body1 and that slow combustion1 or1 as ,liebig terms it1 eremacausis1 must continually go on inside our frail mortal tenements2 and more than this1 that we cannot afford to waste our heat4 ,if the body is deprived of heat faster than it can be generated1 death must inevitably occur2 and a very melancholy instance of this remarkable mode of death has lately occurred in ,switzerland to a ,russian gentleman4 ,such another instance of a man being slowly frozen to death within sight and sound of other beings1 through whose veins the blood was flowing at its accustomed temperature 7about #ij ,fahr471 it would be difficult to find1 and it stands forth1 therefore1 as a marked example and illustration of the statement already made1 that living animal organisms are truly a source of heat1 which is as essential to the well-being of the body as meat1 drink1 and air4 ,heat is of two kinds1 and may be either apparent to our senses1 and therefore called sensible heat2 or it may be entirely concealed1 although present in solids1 liquids1 and gases1 and is then termed insensible or latent heat4 ,page #cee ,sensible ,heat4 ,the first effect of this force is a demonstration of its repulsive agency1 and the dilatation or expansion of the three forms of matter whilst under the influence of heat1 admits of very simple illustrations4 ,the expansion of a solid substance1 as1 for instance1 a metal1 on the application of heat1 is apparent by fitting a solid brass cylinder into a proper metal gauge1 which is accurately filed so as to admit the former when perfectly cold4 ,if the brass rod is then heated1 either by plunging it into boiling water or by the application of the flame of a spirit lamp1 its particles are separated from each other2 they now occupy a larger space1 and expansion is the result1 and this is clearly proved by the application of the gauge1 which is no longer capable of receiving it4 7,fig4 #cdc47 ,when1 however1 the latter is cooled1 the opposite result occurs1 the particles of brass return to their old position1 and contraction takes place2 hence it is stated that ,bodies expand by heat and contract by cold2 and it is proper to state here that the term cold is of a negative character1 and simply means the absence of heat4 ,illustration3 ,fig4 #cdc4 ,a ,b4 ,cylinder of brass4 ,c ,d4 ,iron gauge1 admitting ,a ,b longitudinally1 and also in the hole ,e when cold1 but excluding ,a ,b when the latter is heated and expanded4 ,solid bodies do not expand equally on the application of the same amount of heat2 thus1 a bar of glass one inch square and one thousand inches long would only expand one inch whilst heated from the freezing to the boiling point of water4 ,a bar of iron one inch square and eight hundred inches long would expand one inch in length1 through the same degrees of heat2 and a bar of lead one inch square and three hundred and fifty inches long would also dilate one inch in length4 ,hence1 ,lead expands in volume #a_/cejth4 ,iron #a_/hjjth4 ,glass #a_/ajjjth4 ,the unequal expansion of the metals is well illustrated by an experiment devised by ,dr4 ,tyndal1 the respected ,professor of ,natural ,philosophy in the ,royal ,institution of ,great ,britain1 and is arranged as follows3--,a long bar of brass and another of iron are supported on the ,page #cef edges of two pieces of wood placed at an angle1 and resting against the sides of a mahogany framework4 ,the metallic bars only touch one end of the frame1 and are in metallic communication with a piece of brass inserted there1 and forming part of a conducting chain connected with a voltaic battery2 when heat is applied to both bars they expand unequally2 the brass bar dilates first1 and filling up the minute space left between the two ends of the frame1 touches another brass plate and instantly completes the voltaic circuit1 when a coil of platinum wire becomes ignited1 showing the fact of expansion2 and secondly1 the difference in the power of dilatation possessed by each is clearly shown by removing the two angular supports of wood1 when the iron falls away1 whilst the brass remains and still completes the voltaic circuit4 7,fig4 #cdd47 ,illustration3 ,fig4 #cdd4 ,a ,a4 ,the brass bar which has expanded by the heat from the gas jet ,b1 and making the contact between the brass plates in connexion with the binding screws ,c ,c1 the voltaic circuit is completed1 and a coil of platinum wire in the glass tube ,d1 is immediately ignited4 ,the iron bar at ,e ,e has not expanded sufficiently1 which is shown afterwards by removing the angular wooden supports ,k ,k1 when the iron falls off1 and the brass remains on the two ledges of the mahogany framework ,l ,l ,l4 ,the force exerted by the expansion of solids is enormous1 and reminds us again of the amazing power of all the imponderable agents2 and it is truly wonderful to notice how the entry of a certain amount of heat into and between the particles of metals1 or other solids1 endues them with a mechanical force which is almost irresistible1 and is capable of working much harm4 ,kussn made an experiment with an iron sphere1 which he heated from a temperature of #cb ,fahr4 to #bab ,fahr41 and he found that the expansion of the ball exerted a force equal to #djjj atmospheres--i4e4 #djjj #ae--on every square inch of surface1 or a pressure equal to thirty millions of pounds2 the entry of only #ahj of heat into the iron sphere produced this remarkable result1 just as ,faraday has calculated that a single drop of water contains a sufficient quantity of electricity to produce a result equal to the most powerful flash of lightning1 provided the electricity of quantity in the drop of water is converted into electricity of high tension or intensity4 ,the practical applications of this well-known property of solids with respect to heat are very numerous2 thus1 the iron bullet-moulds are always made a little larger than the requisite size1 in order to allow for the expansion of the hot liquid lead1 and the contraction of the cold metal4 ,the tires of wheels and the hoops of casks are usually placed on whilst hot1 in order that the subsequent contraction may bind the spokes ,pg #ceg and fellies1 or the staves1 closely together4 ,if an allowance was not made for the expansion and contraction of the iron rails on the permanent ways of railroads1 the regularity of the level would be constantly destroyed1 and the position of the rails1 chairs1 and sleepers would be most seriously deranged2 indeed it is calculated that the railway bars between ,london and ,manchester are five hundred feet longer in the summer than in the winter4 ,the walls of the ,cathedral of ,armagh1 as also those of the ,conservatoire des ,art et ,mtiers1 were brought back to a nearly perpendicular position1 by the insertion 7through the opposite walls7 of great bars of iron1 which being alternately heated1 expanded1 and screwed up tight1 then cooled and contracted1 gradually corrected the bulging out of the walls or main supports of these buildings4 ,the principle of these famous practical experiments is neatly illustrated by means of an iron framework with a bar of iron placed through both its uprights1 and screwed tight when hot2 on cooling1 contraction occurs1 which is shown by a simple index4 7,fig4 #cde47 ,illustration3 ,fig4 #cde4 ,the iron frame1 with ,c ,c1 wrought-iron bar heated by putting on the semicircular piece of iron ,e ,e1 which is first made red-hot1 and as the heat is communicated to the wrought iron rod ,c ,c1 it is screwed up tight by the nut ,k4 ,g ,g4 ,the index attached to the iron frame screwed up when hot2 the arms come together at ,p1 and separate further to ,h ,h as the contraction takes place by cooling the bar ,c ,d4 ,it has often been remarked that there is no rule without an exception1 and this applies in a particular instance to the law that bodies expand by heat and contract by cold--viz41 in the case of ,rose's fusible metal1 which consists of ,two parts by weight of bismuth1 ,one part lead1 ,one part tin4 ,to make the alloy properly1 the lead is first melted in an iron ladle1 and to this are added first the tin1 and secondly the bismuth2 the whole is then well stirred with a wooden rod1 and cast into the shape of a bar4 ,page #ceh ,when placed in the pyrometer and heated1 the bar expands progressively till it reaches a temperature of #aaa ,fahr42 it then begins to contract1 and is rapidly shortened1 until it arrives at #aef ,fahr41 when it attains a maximum density1 and occupies no more space than it would do at the freezing-point of water4 ,the bar1 after passing #aef1 again expands1 and finally melts at about #bja1 which is #aa below the boiling-point of water4 ,fusible metal is sometimes made into teaspoons1 which soften and melt down when stirred in a cup of hot tea or basin of soup1 to the great surprise and bewilderment of the victim of the practical joke4 ,unequal expansion is familiarly demonstrated with a bit of toasted bread1 which curls up in consequence of the surface exposed to the fire contracting more rapidly than the other2 and the same fact is illustrated with compound flat and thin bars of iron and brass1 which are fixed and rivetted together2 when heated1 the compound bar curves1 because the iron does not expand so rapidly as the brass1 and of course forms the interior of the curve1 whilst the brass is on the exterior4 ,the experiment with the compound bar is made more conclusive and interesting by arranging it with a voltaic battery and platinum lamp4 ,one of the wires from the battery is connected with the extremity of the compound bar1 and as long as it remains cold1 no curve or arch is produced1 but when heat is applied1 the bar curves upwards1 and touching the other wire of the battery1 the circuit is completed1 and the platinum lamp is immediately ignited4 7,fig4 #cdf47 ,illustration3 ,fig4 #cdf4 ,a ,b4 ,compound bar resting on two blocks of wood4 ,the end ,a is connected with one of the wires from the battery4 ,the circuit is completed and the platinum lamp ,d ignited directly the bar curves upwards by the heat of the spirit lamp1 and touches the wire ,c ,c connected with the opposite pole of the battery4 ,the expansion and contraction of liquids by heat and cold is also another elementary truth which admits of ample illustration1 and indeed introduces us to that most useful instrument called the thermometer4 ,if a flask is fitted with a cork through which a long glass tube1 open ,page #cei at both ends1 is passed1 and then carefully filled with water coloured with a little solution of indigo1 so that when the cork and tube are placed in the neck1 all the air is excluded1 a rough thermometer is thus constructed1 which1 if placed in boiling water1 quickly indicates the increased temperature by the rising or expansion of the coloured water inside the flask4 7,fig4 #cdg47 ,illustration3 ,fig4 #cdg4 ,expansion of liquids shown at ,a by the coloured water rising in the tube from the flask1 which is quite full of liquid1 and heated by boiling water4 ,b4 ,the expansion of the water heated by the spirit-lamp is shown by the rising of the piston and rod ,c ,c4 ,d represents a retort filled up like ,a to show the expansion of a liquid by heat4 ,the thermometer embraces precisely the same principle as that already described in ,fig4 #cdg1 with this difference only1 that the tube is of a much finer bore1 and the liquid employed1 whether alcohol or mercury1 is boiled and hermetically sealed in the tube1 so that the air is entirely excluded4 ,to make a thermometer1 a tube with a capillary bore is selected of the proper length2 it is then dipped into a glass containing mercury1 so that the tube is filled to the length of half an inch with that metal4 ,the half-inch is carefully measured on a scale1 and the place the mercury fills in the tube marked with a scratching diamond2 the mercury is then shaken half an inch higher1 and again marked1 and this proceeding is continued until the whole tube is divided into half inches4 ,the object of doing this is to correct any inequalities ,page #cfj;in the diameter of the bore of the glass tube1 because if wider at one part than another1 the spaces filled with the mercury are not equal2 as the bore is usually conical1 the careful measurement of the tube with the half inch of mercury in the first place gives the operator at once a view of the interior of his tube1 and enables him to graduate it correctly afterwards4 7,fig4 #cdh47 ,illustration3 ,fig4 #cdh4 ,a ,b4 ,magnified view of the bore of one of the thermometer tubes which are made by rapidly drawing out a hollow mass of hot glass whilst soft and ductile1 consequently the bore must be conical1 and larger at one end than the other4 ,the next step is to heat one extremity by the lamp and blowpipe1 and whilst hot1 to blow out a ball upon it2 if this operation were performed with the mouth1 moisture from the breath would deposit inside the fine bore of the glass tube1 and injure the perfection of the thermometer afterwards4 ,in order to prevent any deposit of water1 the bulb is blown out1 whilst red-hot1 with the air from a small caoutchouc bag fitted on to the other extremity of the tube4 ,the operator now marks off the intended length of his thermometer1 and above that point the tube is again softened with the flame and blowpipe1 and a second bulb blown out4 7,fig4 #cdi a47 ,illustration3 ,fig4 #cdi a4--,no4 #a4 ,first bulb4 ,the intended length of the thermometer is shown at the little cross4--,no4 #b is the second bulb placed above the cross4 ,the open end of the tube is now placed under the surface of some pure1 clean1 dry quicksilver1 and heat being applied to the upper bulb1 the air expands and escapes through the mercury1 and as the tube cools a vacuum is produced1 into which the mercury passes4 ,by this simple method1 the mercury is easily forced into the tube1 as otherwise it would be impossible to pour the quicksilver into the capillary bore of the intended thermometer4 7,fig4 #cdi b47 ,illustration3 ,fig4 #cdi b4 ,heating and expanding the air in the top bulb1 so that when cool the mercury in the glass ,a1 may rise into the tube and fill the bulb ,b4 ,the tube is now taken from the glass containing the mercury1 and simply inverted2 but in consequence of the very narrow diameter of the bore the air will not pass out of the first bulb until heat is applied1 when the air expands1 and the ,page #cfa mercury1 first stationary in the second bulb1 will now displace the air1 and fall into the first bulb when the tube is again cool4 ,the ball1 ,no4 #a 7,fig4 #cdi a71 is now full of mercury1 and there is also some left in ,no4 #b2 in the next place1 the tube is supported by a wire1 and held over a charcoal fire1 when it is heated throughout its entire length1 and the mercury being boiled expels the whole of the air1 so that there is nothing inside the bulbs and capillary bore but mercury and its vapour4 7,no4 #a1 ,fig4 #cej47 ,the open end of the intended thermometer is now temporarily closed with sealing-wax1 and the whole allowed again to cool with the sealed end uppermost1 so that the ball ,no4 #b1 ,fig4 #cej1 and the tube above it1 are quite filled with quicksilver4 ,after cooling1 the tube is placed at an angle with the sealed end uppermost1 and1 guided by experience1 the operator heats the lower bulb so as to expand enough mercury into the upper one to leave space for the future expansion and contraction of the mercury in the tube1 which has now to be hermetically sealed4 ,this is done by dexterously heating the tube at the cross whilst the mercury in the first bulb is still expanded2 and by drawing it out rapidly with the help of the heat obtained from the lamp and blowpipe1 the second bulb is separated from the first at the little cross 7,b1 ,no4 #c1 ,fig4 #cej71 and the thermometer tube at last properly filled with quicksilver1 and hermetically closed4 7,no4 #d1 ,fig4 #cej47 ,illustration3 ,fig4 #cej4--,no4 #a4 ,boiling quicksilver in the tube with two bulbs4--,no4 #b4 ,tube cooled1 with the sealed end uppermost4--,no4 #c4 ,mercury in first bulb expanded by lamp ,a1 and at the proper moment hermetically sealed by the flame urged by the blowpipe at ,b4 ,the upper bulb and tube to the cross being drawn away and separated4--,no4 #d4 ,thermometer tube containing the requisite quantity of mercury1 hermetically sealed1 and now ready for graduation4 ,page #cfb ,in order to procure a fixed starting-point1 the thermometer tube is placed in ice1 with a scale attached2 the temperature of ice never varies1 it is always at #cb degrees4 ,when1 therefore1 the mercury has sunk to the lowest point it can do by exposure to this degree of cold1 the place is marked off in the scale1 and represents that position in the graduated scale where the freezing point of water is indicated4 ,the tube is placed in the next place in a vessel of boiling water1 care being taken that the whole tube is subject to the heat of the water and the steam issuing from it1 and when the mercury has risen to the highest position attainable by the heat of boiling water1 another graduation is made which indicates #bab degrees--viz41 the boiling point of water4 ,this graduation should be made when the barometer stands at #cj inches1 because the boiling point of water varies according to the weight of the superincumbent air pressing upon it4 ,between the graduation of the freezing and the boiling point of water the space is divided into #ahj parts1 which added to #cb make up the boiling point of water to #bab degrees1 being the graduation of ,fahrenheit1 who was an instrument-maker of ,hamburg4 ,why he divided the space between the freezing and boiling point of water nobody appears to know1 unless he took a half circle of #ahj degrees as the best division of space4 ,if the thermometer contains air the mercury divides itself frequently into two or three slender threads1 each separated from the other in the capillary bore1 and thus the instrument is rendered useless until the threads again coalesce4 ,if the thermometer has been well made1 and is quite free from air1 it may be tied to a string and swung violently round1 when the centrifugal force drives the slender threads of mercury to their common source--viz41 the bulb containing the quicksilver1 and the whole is again united4 ,the string must be attached1 of course1 to the top of the thermometer scale4 ,when travelling on the ,continent it is sometimes desirable to be able to read the thermometers which are graduated in a different manner to that of ,fahrenheit4 ,in ,france the ,centigrade scale is preferred1 and in many parts of ,germany ,reaumur's graduation4 ,the difference of the graduation is seen at a glance4 ,in the ,centigrade the freezing point is #j1 the boiling point #ajj4 ,reaumur #j1 #hj4 ,fahrenheit #cb1 #bab4 ,the number of degrees1 therefore1 between boiling and freezing is #ajj in the ,centigrade1 #hj in ,reaumur1 and 7#bab-cb1 that is7 #ahj in ,fahrenheit4 ,if1 then1 the letters ,c1 ,r1 ,f1 be taken to denote the number of degrees from the freezing point at which the mercury stands in the ,centigrade1 ,reaumur1 and ,fahrenheit thermometers1 we have the following proportions3-- 7#a47 #ajj3 #hj 33 ,c3 ,r1 whence ,c #e_/d of ,r1 or ,r #d_/e of ,c4 7#b47 #ahj3ajj 33 ,f3 ,c1 whence ,f #i_/e of ,c1 or ,c #e_/i of ,f4 7#c47 #ahj3 #hj 33 ,f3 ,r1 whence ,f #i_/d of ,r1 or ,r #d_/i of ,f4 ,page #cfc ,the following examples will show how to apply these formul3-- 7#a74--,suppose the ,reaumur stands at #bh1 at what height does the ,centigrade stand8 ,we have ,c #e_/d of ,r 7in this case71 #e_/d of #bh #ce3 that is1 the ,centigrade stands at #ce4 7#b74--,suppose ,fahrenheit to stand at #da1 what will ,reaumur stand at8 ,r #d_/i of 7#da-cb7 7that is1 the number above freezing in ,fahr47 #d_/i of #i #d4 ,reaumur stands at #d4 7#c74--,suppose ,fahrenheit stands at #bc1 what will the ,centigrade stand at8 ,c #e_/i of ,f #e_/i of 7#cb-bc7 #e_/i of #i #e below freezing 7or-#e74 7#d74--;,if ,fahrenheit stands at #d below #j1 what will ,reaumur indicate8 ,r #d_/i of ,f #d_/i of 7#cb #d7 #d_/i of #cf #af below #j 7or-#af74 ,the only liquid which has the exceptional property of expanding by cold is water1 and it will be seen presently that this curious anomaly is of the greatest importance in the economy of nature4 ,if a box containing a mixture of ice and salt is placed round the top of a long cylindrical glass containing water at a temperature of #fj ,fahr41 the intense cold of the freezing mixture1 which is zero--that is to say1 #cb below the freezing point of water--very soon reduces the temperature of the water contained in the glass1 and as it becomes colder it contracts1 is rendered heavier1 and sinks to the bottom of the vessel1 and its place is taken by other and warmer water4 ,this circulation commencing downwards1 proceeds till the water has attained a temperature of about #dj ,fahr41 when the maximum density is obtained and the circulation stops1 because after sinking below #dj the cold water becomes lighter1 and continues to be so until it freezes1 and of course1 being of a less specific gravity than the warmer water1 it floats 7like oil on water7 upon its surface2 so that a small thermometer placed at the bottom of the jar indicates only #dj ,fahr41 whilst the solid ice enveloping the other or second thermometer placed at the top may be as low as #bi1 or even lower1 according to the quantity of ice and salt used in the box surrounding the top of the glass4 7,fig4 #cea47 ,illustration3 ,fig4 #cea4 ,a ,b4 ,long cylindrical glass containing water and two thermometers2 the one at the bottom shows a temperature of #dj2 the other at the top #cb1 or even lower1 ,c ,c ,c ,c4 ,section of box containing the ice and salt1 and standing on four legs1 two of which are shown at ,d ,d4 ,page #cfd ,the importance of this curious anomaly cannot be overrated4 ,if water did not possess this rare property1 all the seas1 rivers1 canals1 lakes1 c41 would gradually become impassable from the presence of enormous blocks of ice formed during the winter4 ,the whole bulk of water contained in them would have to sink below #cb before it could solidify provided water increased in density or continued to contract by cold4 ,having once solidified1 the warmth of the rays from a summer's sun would certainly melt a great deal of the ice1 but not the whole1 and winter would come again before the solid masses had disappeared4 ,the ocean could not be navigated in safety even near our own shores1 in consequence of the vast icebergs that would be formed1 and float about and jostle each other even in the ,british ,channel4 ,the earth has been wonderfully prepared for ,god's highest work--,man1 and in nothing is this supreme wisdom more apparent than in the fact that water offers the only known exception to the law that bodies expand by heat and contract by cold4 ,the expansion of gases by heat and contraction by cold take place in obedience to a law to which there is no exception1 except in degree4 ,it was discovered in #ahja by ,m4 ,gay ,lussac1 of ,paris1 and also about the same period by the famous ,english philosopher who established the atomic theory--viz41 by ,dr4 ,dalton4 ,since these experiments and calculations ,rudberg1 ,magnus1 and ,regnault have made other researches1 and their successive experiments give the following results3-- ,vols4 of air4 ,volumes4 ,dalton1 ,gay ,lussac #ajjj heated from #cb to #bab became #acge ,rudberg #ajjj #acfe ,magnus1 ,regnault #ajjj #acff4e ,as a natural result1 air at #cb ,fahr1 expands #a_/dia part of its volume for every degree of heat on the scale of ,fahrenheit2 and a volume of air which measures #dia cubic inches at #cb will measure #dib at #cc1 #dic at #cd1 and so on4 ,the exception is only in degree1 and ,magnus and ,regnault discovered by their searching experiments that the gases easily liquified are more expansible by heat than air and those gases 7such as oxygen1 hydrogen1 and nitrogen7 which have never been liquified4 ,the expansion of air is easily shown by placing the open end of a tube with a large bulb blown at the other extremity1 under the surface of a little coloured water2 on the application of heat the air expands and escapes1 and its place is taken1 when cool1 by the coloured liquid4 ,such an arrangement represents the first thermometer constructed by ,sanctorio about ,a4,d4 #afjj1 which might certainly answer for rough purposes1 but as the ascent and descent of the fluid depend on the bulk of air contained in the bulb1 and as this is affected by every change of the height of the barometer1 no satisfactory indication of an increase or decrease of temperature could be obtained with it1 although the instrument itself is interesting in an historical point of view1 and in a ,page #cfe modified form as an air thermometer has been employed by ,sir ,john ,leslie1 under the name of the ,differential ,thermometer1 in his refined and delicate experiments with heat4 ,illustration3 ,fig4 #ceb ,a4 ,sanctorio's original air thermometer2 the expansion and contraction of the air in the bulb indicate the rise or fall of the temperature4 ,the cork is merely a support1 and is not fitted into the bottle air-tight4 ,b ,c4 ,the differential thermometer4 ,when both bulbs are subjected to a uniform temperature1 no movement of the fluid shown at ,d occurs2 but if the bulb ,b is put into any place warmer than the position of the bulb ,c1 then the air expands in ,b1 and drives the coloured liquid1 which consists of carmine dissolved in oil of vitriol1 up the scale attached to the stem of the bulb ,c4 ,fire balloons are a good example of the expansion of gases1 and the levity of the air thus increases in bulk was taken advantage of by ,montgolfier in the construction of his famous balloon1 which1 with a cage containing various animals1 ascended1 in the presence of the ,king and royal family of ,france1 at ,versailles2 and in spite of huge rents in two places1 it rose to a height of #addj feet1 and after remaining in the air for eight minutes1 fell to the ground at the distance of #aj1bjj feet from the place whence it started1 without injury to the animals4 ,when it is considered that a volume of air heated from #cb to #dia is doubled1 and tripled when heated to #ihb1 it will at once be understood how great must be the ascending power of such balloons1 provided the air within them is kept sufficiently hot4 ,that gallant aronaut1 ,pilate de ,rozier1 offered himself to be the first arial navigator2 and having joined ,montgolfier1 they made three successful ascents and descents with a large oval-shaped balloon1 forty-eight feet in diameter1 and seventy-four feet high4 ,on the fourth occasion he ascended to a height of #bfb feet1 but in the descent a gust of wind having blown the machine over some large trees of an adjoining garden1 the situation of the brave aronaut was extremely dangerous1 and if he had not possessed the strongest presence of mind1 and at once ,page #cff given the balloon a greater ascending power1 by rapidly supplying his stove with some straw and chipped wood1 he might on this occasion have met with that untimely end which subsequently1 in another rash aronautic adventure1 befell this brave but foolhardy ,frenchman4 ,on descending again1 he once more1 and without the slightest fear1 raised himself to a considerable height by feeding his fire with chopped straw4 ,some time after he ascended1 in company with ,m4 ,giroud de ,vilette1 to the height of #ccj feet1 hovering over ,paris at least nine minutes1 in sight of all the inhabitants1 and the machine keeping all the while perfectly steady4 ,the danger in using this method of inflating the balloon arises from the possibility of generating gas1 which escaping unburnt into the body of the balloon1 may accumulate and blow up1 or burn afterwards4 ,illustration3 ,fig4 #cec4 ,a ,b4 ,wessel's gas stove1 with ring of gas jets lighted inside2 the air rushes in the direction of the arrows1 ,c ,c1 and escaping at the top of the chimney1 ,d ,d1 soon fills the air or fire balloon1 which is usually made of paper4 ,fire balloons1 as usually made1 are very dangerous toys1 and may sometimes prove rather costly to the person who may send them off1 in consequence of their being blown by the wind on a hay or corn rick1 or other combustible substances4 ,the safest mode of using fire balloons is to fill them with hot air from a lighted gas stove 7,wessel's1 for instance72 the balloons may then be used in large rooms1 or out in the air1 without fear of doing any harm to neighbouring property1 as of course the stove and the fire remain behind1 and will fill any number of air balloons4 7,fig4 #cec47 ,after all the fuss made about the novelty of the ,american hot-air engine1 it is somewhat amusing to look back to the records of civil engineering1 and in the ,transactions of the ,institution of ,civil ,engineers1 to read ,mr4 ,james ,stirling's account of his improved air engine1 in which the great expansion of air mentioned at p4 #cfe has been successfully applied4 ,the engine was constructed about the year ,page #cfg #ahdc1 and the principle1 discovered thirty years before by ,mr4 ,r4 ,stirling1 will be comprehended by reference to the cut4 7,fig4 #ced47 ,illustration3 ,fig4 #ced4 ,stirling's air engine4 ,two strong air-tight vessels are connected with the opposite ends of a cylinder1 in which a piston works in the usual manner4 ,about four-fifths of the interior space in these vessels is occupied by two similar air-tight vessels or plungers1 which are suspended to the opposite extremities of a beam1 and capable of being alternately moved up and down to the extent of the remaining fifth4 ,by the motion of these interior vessels1 which are filled with non-conducting substances1 the air to be operated upon is moved from one end of the exterior vessel to the other1 and as one end is kept at a high temperature1 and the other as cold as possible1 when the air is brought to the hot end it becomes heated1 and has its pressure increased2 and when it is brought to the cold end1 its heat and pressure are diminished4 ,now1 as the interior vessels necessarily move in opposite directions1 it follows that the pressure of the enclosed air in the one vessel is increased1 while that of the other is diminished4 ,a difference of pressure is thus produced upon the opposite sides of the piston1 which is thereby made to move from the one end of the cylinder to the other1 and by continually reversing the motion of the suspended bodies or plungers1 the greater pressure is successively thrown upon a different side1 and a reciprocating motion of ,page #cfh the piston is kept up4 ,the piston is connected with a fly-wheel in any of the usual modes2 and the plungers1 by whose motion the air is heated and cooled1 are moved in the same manner1 and nearly at the same relative time1 with the valves of a steam engine4 ,the pressure is greatly increased and made more economical by using somewhat highly-compressed air1 which is at first introduced1 and is afterwards maintained1 by the continued action of an air-pump4 ,the pump is also employed in filling a separate magazine with compressed air1 from which the engine can be at once charged to the working pressure4 ,mr4 ,stirling's chief improvement consists in saving all or nearly all the heat of the expanded air after it has done its work1 by passing it from the hot to the cold end of the air vessel through a multitude of narrow passages1 whose temperature is at the beginning of the tubes nearly as great as that of the hot air1 but gradually declines till it becomes nearly as low as the coldest part of the air vessel4 ,the heat is therefore retained by these passages1 so that when the mechanism is reversed1 the cold air returns again through these hot pipes1 and is thus made nearly hot enough by the time it reaches the heating vessel to do its work4 ,thus1 instead of being obliged to supply at every stroke of the engine as much heat as would be sufficient to raise the air from its lowest to its highest temperature1 it is necessary to furnish only as much as will heat it the same number of degrees by which the hottest part of the air vessel exceeds the hottest part of the intermediate passages4 ,this portion of the engine may be called the economical process1 and represents the foundation of all the success to which it has attained in producing power with a small expenditure of fuel4 ,no boiler being required1 of course the danger of explosions is much lessened4 ,the higher the pressure under which the engine was worked the greater was the effect produced4 ,a small engine on this principle was worked to a pressure of #cfj pounds on the square inch2 and perhaps the best popular notion of the novelty in the arrangement is that suggested by ,mr4 ,george ,lowe1 who compared the economical part of the machine to a ,jeffrey's ,respirator used by consumptive patients4 ,the heat from the air expired being retained by the lamin1 and again used when cold air is inspired or drawn into the lungs4 ,mr4 ,stirling states that the consumption of fuel as compared to the steam engine which the air engine had replaced was as #f to #bf2 the same amount of work being now performed by about six cwt4 of coals which had formerly required about twenty-six cwt41 though he ought to have stated that the steam engine removed was not of the best construction1 nor had the boiler any close covering4 7,fig4 #ced47 ,conduction of ,heat4 ,this property of heat with reference to matter1 and the consideration of the curious manner in which it creeps1 as it were1 through solid substances1 brings the thoughtful mind at once to the bold question of ,what is heat8 ,is it to be regarded as something real or material8 or ,page #cfi must it be considered only as a property or state of matter8 ,these questions are not to be solved easily1 and they demand a considerable amount of experiment and reasoning even to appreciate their meaning4 ,if a red-hot ball is placed in the focus of a concave metallic speculum1 it gives out certain emanations that are quite invisible1 but which are reflected from the surface of the mirror in the same manner as visible rays of light1 and may be collected in the focus of another and second concave speculum1 when they can be concentrated on to a bit of phosphorus1 and will cause the combustion of that substance4 ,if the air from a pair of bellows is blown forcibly across the rays of heat as they are being concentrated upon the phosphorus1 the rays are not moved from their course1 they are no more blown away than a sunbeam darting through an aperture in a cloud on a stormy1 windy day4 ,the heat has1 therefore nothing to do with the air1 and is wholly independent of that medium in its passage from one mirror to the other4 ,such an experiment as that described would at once suggest the idea that heat is a matter sui generis1 a component part of all bodies1 and given off from incandescent matter1 the sun1 c41 and that it may be propagated through space much in the same manner as light4 7,fig4 #cee47 ,the mechanism may be very much like the corpuscular movement of light as defined by ,sir ,isaac ,newton1 and already explained in another portion of this book4 ,hence it has been supposed that heat is propagated through the air1 water1 and solid substances by a direct emission of material particles from the heat-giving agent1 and that these molecules of heat force their way into1 or along1 or through them1 according to circumstances4 ,illustration3 ,fig4 #cee4 ,heat reflected by mirror1 but not blown away by air from bellows4 ,certain bodies are almost transparent to heat rays1 such as air1 whilst others take an intermedial position1 and only stop a certain quantity of the heat molecules1 such as rock crystals1 mirror glass1 and alum4 ,a third class of bodies absorbs the heat plentifully1 such as charcoal1 black cloth1 c42 and a fourth1 when polished and placed at the proper angle1 reflects or throws off the heat1 as in the case of polished mirrors4 ,the transparency or opacity of substances 7so far as light is concerned7 ,page #cgj does not affect the transmission of heat4 ,light of every colour and from all sources is equally transmitted by all transparent bodies in the liquid or solid form1 but this is not the case with heat4 ,the rays of heat emitted by the sun and other luminous bodies have properties quite different to the rays of light with which they are accompanied4 ,from these statements it will be evident that the material theory of heat is surrounded with difficulties and anomalies that cannot be reconciled the one with the other1 or neatly adapted1 fitted in1 and dovetailed with all the puzzling phenomena that arise4 ,our knowledge of the theory of heat has been greatly assisted by the researches of ,melloni1 who has demonstrated that different species of rays of heat are given off by the same body at different temperatures1 which may be distinctly sifted and separated from each other4 ,long before the experiments of ,melloni philosophers had endeavoured to weigh heat2 trains of the most delicate levers were exposed1 without effect1 to the action of heat rays2 and all attempts1 experimental as well as theoretical1 to define heat by the material theory1 are imperfect1 crude1 and unsatisfactory4 ,we are perforce obliged to adopt another theory1 and the one that obtains the greatest favour1 as offering the best definition of heat1 is the dynamical theory1 which is more or less analogous to the undulatory theory of light4 ,at pages #bfb1 #cbh1 #cce1 this theory has been partly explained1 and in speaking of it again1 great care must be taken not to confuse the undulations of heat with those of light4 ,the sun and the stars swim in a molecular medium1 and #ci1ahj vibrations or waves must occur in one inch to produce the sensation of red light1 and #eg1dij undulations in the space of one inch to produce a violet light4 ,as vibrations of the ethereal molecules affect the eye1 so there may be other nerves in our bodies which are peculiarly sensitive to the waves of heat4 ,it requires eight vibrations of the air to occur in a second to produce an audible sound2 whilst if the vibrations of the air amount to #be1jjj per second they cannot be appreciated by the human ear1 although it is possible to conceive that the ears of certain animals may be so susceptible of rapid vibrations that they may be able1 for certain wise purposes of the ,creator1 to appreciate sounds which are inaudible to human ears4 ,melloni exhibited a spectrum to a number of persons1 and found that there was more light apparent to some eyes than to others4 ,lubeck put a scarlet cloth on a donkey1 and found that the two were frequently confounded together by the eyes of many spectators4 ,these facts indicate that there may be vibrations of molecules that produce the sensation of heat1 but which do not affect the nerves that are sensitive to the action of light waves1 and vice vers2 and it is also probable that all these different undulations1 some affording heat and some light1 may be generated and propagated through space1 as from the sun2 or through shorter distances1 as from burning lamps and fires1 without in any way interfering with or impeding each other's progress4 ,the dynamical theory seems to offer the best idea of the transmission ,page #cga of heat which is carried1 conducted1 or propagated through solids with variable rapidity1 either by the vibration of the constituent molecules of the body itself1 or by the undulation of a rare subtle fluid which pervades them4 ,if a copper and iron wire of the same length and diameter are bound together and heated at the point of union1 the waves of heat travel faster through the copper than the iron1 and the former is said to be the best conductor of heat2 and the fact itself is demonstrated by placing a bit of phosphorus at the end of each metallic wire1 and it will be found by experiment that the combustible substance melts first and takes fire on the copper1 and that a considerable interval of time elapses before the phosphorus ignites on the iron4 ,illustration3 ,fig4 #cef4 ,c4 ,copper wire bound at ,a to ,i1 an iron wire4 ,after the heat of the lamp has been applied for about five minutes the heat travels to ,c first1 and ignites the bit of phosphorus placed there4 ,after some time has elapsed the phosphorus at ,i also ignites4 ,the same fact is exhibited in a most striking manner by inserting a series of rods of equal lengths and thicknesses in the side of a rectangular box1 allowing them to pass across the interior to the opposite side4 ,the rods are composed of wood1 porcelain1 glass1 lead1 iron1 zinc1 copper1 and silver1 and have attached to each of their extremities1 by wax or tallow1 a clay marble4 ,when the water placed in the box is made to boil1 the heat passes along the different rods1 and melting the wax or tallow1 allows the marble to drop off4 ,consequently the first marble would drop from the silver rod1 the next from the copper1 the third from the iron1 the fourth from the zinc1 the fifth from the lead1 whilst the porcelain1 glass1 and wooden rods would hardly conduct 7in several hours7 sufficient heat to melt the wax or tallow1 and discharge the marbles4 ,conduction of ,metals4 ,gold #ajjj ,silver #igc ,copper #hih4b ,iron #cgd4c ,zinc #cfc ,lead #agi4f ,page #cgb ,the experiment is made more striking if the marbles are allowed to fall on a lever connected with the detent of a clock alarum1 which rings every time a marble falls from one of the rods4 7,fig4 #ceg47 ,during a cold frosty day1 if the hand is placed in contact with various substances1 some appear to be colder than others1 although all may be precisely the same temperature2 this circumstance is due to their conducting power3 and a piece of slate seems colder than a bit of chalk1 because the former is a much better conductor than the latter1 and carries away the heat from the body with greater rapidity1 and diffuses it through its own substance4 ,illustration3 ,fig4 #ceg4 ,a ,b4 ,trough containing boiling water1 heated by gas jets below4 ,c4 ,the eight rods and marbles attached1 one of which has fallen4 ,d4 ,the tray to receive the marbles4 ,the gradual passage of heat along a bar of iron as compared with one of copper1 is well illustrated by supporting the ends of the two bars on the top of the chimney of an argand lamp1 whilst the other extremities are held in a horizontal position by little blocks of wood4 ,if marbles are attached by wax to the under side1 they fall off as the heat travels along the metallic bars1 and more rapidly from the copper than the iron1 because the former is a better conductor of heat than the latter4 7,fig4 #ceh47 ,illustration3 ,fig4 #ceh4 ,a4 ,section of an argand gas lamp1 with a copper chimney supporting the ends of the bars of copper and iron marked ,c and ,i4 ,the balls have fallen from ,c1 the copper bar4 ,from the experiments of ,mayer1 of ,erlangen 7,ann4 de ,ch41 ,,xxx471 it would appear that the conducting powers of different woods are to a certain extent to be regarded as in the inverse proportion to their specific gravities--i4e41 the greater the density of the wood the less conducting power1 and the contrary4 ,if a cylindrical bar or thick tube of brass1 six inches long1 and about two inches in diameter1 is attached to a wooden cylinder of the same size1 the conducting powers of the two substances are well displayed by first straining a sheet of white paper over the brass1 and then holding it in the flame of a spirit lamp4 ,the heat being conducted rapidly away by the metal will not scorch the paper1 until the whole arrives at a uniform high temperature2 whereas the paper is rapidly burnt when ,page #cgc strained over the wooden cylinder1 because the heat of the flame of the lamp is concentrated upon one point1 and is not diffused through the mass of the wood4 7,fig4 #cei47 ,in the course of the highly philosophical experiments of ,sir ,h4 ,davy1 which led him gradually to the discovery of the construction of the safety lamp1 he connected together1 by a copper tube of a small bore1 two vessels1 each containing an explosive mixture composed of fire damp and air4 ,when the mixture was fired in one vessel he found that the flame did not appear to be able to travel1 as it were1 across the bridge--viz41 the copper tube--and communicate with the other magazine1 because it was deprived of its heat whilst passing through the tube1 and was no longer flame1 but simply gaseous matter at too low a temperature to effect the inflammation of the mixture in the second box4 ,illustration3 ,fig4 #cei4 ,cylinder1 half brass and half wood4 ,the paper strained over the wood is taking fire4 ,the other extremity1 shaded1 is the brass portion4 ,a mass of cold metal may be suddenly applied to a small flame1 such as that of a night light1 and depriving it rapidly of heat 7like the case of the unfortunate ,russian described at page #ced71 it is almost immediately extinguished 7fig4 #cfj71 not by the mere exclusion of the oxygen of the air1 but on account of the withdrawal of the heat necessary for the maintenance of the combustion4 ,illustration3 ,fig4 #cfj4 ,a4 ,small flame from night light4 ,b ,c4 ,large mass of cold copper wire open at both ends to place over flame1 and by conduction of the heat to extinguish it4 ,sir ,h4 ,davy first thought of making his safety lamp with small tubes1 which would supply fresh air1 and carry off the burnt or foul air1 at the ,page #cgd same time they were to be so narrow that no flame could pass out of his lamp to communicate with an outer explosive atmosphere2 and in speaking of his lamp with tubes he says3--,i soon discovered that a few apertures1 even of very small diameter1 were not safe unless their sides were very deep2 that a single tube of one-twenty-eighth of an inch in diameter1 and two inches long1 suffered the explosion to pass through it2 and that a great number of small tubes1 or of apertures1 stopped explosion1 even when the depths of their sides was only equal to their diameters4 ,and at last ,i arrived at the conclusion that a metallic tissue1 however thin and fine1 of which the apertures filled more space than the cooling surface1 so as to be permeable to air and light1 offered a perfect barrier to explosion1 from the force being divided between1 and the heat communicated to an immense number of surfaces4 ,i made several attempts to construct safety lamps which should give light in all explosive mixtures of fire damp1 and after complicated combinations1 ,i at length arrived at one evidently the most simple1 that of surrounding the light entirely by wire gauze1 and making the same tissue feed the flame with air and emit light4 ,if a number of square metallic tubes of a fine bore are placed upright side by side1 and a section cut off horizontally1 it would represent the wire gauze which possesses such marvellous powers of sifting away the heat from a flame1 so that it is destroyed in its attempted passage through the metallic meshes2 and of this fact a number of proofs may be adduced4 ,a gas jet delivering coal gas may be placed under a sheet of wire gauze1 the gas permeates the gauze1 and may be set on fire at the upper side1 but the flame is cut off from the mouth of the jet by the cooling action of the wire gauze4 ,the same experiment reversed1 by holding the gauze over the gas burning from the jet1 shows still more decidedly that flame will not pass through the metallic tissue4 7,fig4 #cfa47 ,illustration3 ,fig4 #cfa4 ,a ,a4 ,a number of square tubes placed upright4 ,the arrow shows the direction of the section to obtain a figure like wire gauze4 ,sir ,h4 ,davy again says3 ,though all the specimens of fire damp which ,i had examined consisted of carburetted hydrogen mixed with different small proportions of carbonic acid and common air1 yet some phenomena ,i observed in the combustion of a blower induced me to believe that small quantities of olefiant gas may be sometimes evolved in coal mines with the carburetted hydrogen4 ,i therefore resolved to make all lamps safe to the test of the gas produced by the distillation of coal1 which1 when it has not been exposed to water1 always contains olefiant gas4 ,i placed my lighted lamps in a large glass receiver through which there was a current of atmospherical air1 and by means of a ,page #cge gasometer filled with coal gas1 ,i made the current of air which passed into the lamp more or less explosive1 and caused it to change rapidly or slowly at pleasure1 so as to produce all possible varieties of inflammable and explosive mixtures1 and ,i found that iron gauze wire composed of wires from one-fortieth to one-sixtieth of an inch in diameter1 and containing twenty-eight wires or seven hundred and eighty-four apertures to the inch1 was safe under all circumstances in atmospheres of this kind2 and ,i consequently adopted this material in guarding lamps for the coal mines1 when in ,january1 #ahaf1 they were immediately adopted1 and have long been in general use4 ,the remarkable conducting power of wire gauze is further shown by placing some lumps of camphor on a piece of this material1 and when the heat of a spirit-lamp is applied on the under side of the gauze1 the camphor volatilizes1 and as the vapour is remarkably heavy1 it falls through the meshes of the gauze1 and takes fire2 but the most curious and further illustration of the conducting power of the wire meshes is shown in the fact that the fire does not communicate through the thin film of gauze to the lumps of camphor placed upon it4 ,the camphor may be ignited by applying flame to the upper side of the gauze1 showing that1 although this substance is so exceedingly combustible1 it will not take fire even if placed at no greater distance from flame than the thickness of the wire gauze1 provided the latter material is interposed between it and the flame4 ,a square box made of wire gauze1 with a hole at the bottom to admit a candle or spirit-lamp1 may have a considerable jet of coal gas forced upon it from the outside1 or a large jug of ether vapour poured upon it2 and although the box may be full of flame1 arising from the combustion of the gas or ether1 the fire does not come out of the wire box or communicate with the jet or the ether vapour as it is poured from the jug4 7,fig4 #cfb47 ,illustration3 ,fig4 #cfb4 ,a box made of wire gauze1 with a hole in the bottom to admit a spirit lamp lighted4 ,a hot jug full of the vapour of ether may be poured on to the flame1 but it only burns inside the box1 and does not communicate with that in the jug4 ,sir ,humphrey ,davy's safety lamp consists of a common oil-lamp1 f1 with a wire through the cistern for the purpose of raising or depressing the cotton wick without unscrewing the wire gauze2 b is the male screw fitting the screw attached to the cylinder of wire gauze1 which is made double at the top4 ,the entire lamp is shown at ,a1 whilst the platinum coil which ,sir ,h4 ,davy recommends should be wound round the wick is shown at h4 ,the small ,page #cgf cage of platinum consists of wire of one-seventieth to one-eightieth of an inch in thickness1 fastened to the wire for raising or depressing the cotton wick1 and should the lamp be extinguished in an explosive mixture1 the little coil of platinum begins to glow1 and will afford sufficient light to guide the miner to a safe part of the mine4 ,with respect to this platinum coil1 ,sir ,h4 ,davy gives a careful charge1 and says3--,the greatest care must be taken that no filament or wire of platinum protrudes on the exterior of the lamp1 for this would fire externally an explosive mixture4 ,illustration3 ,fig4 #cfc4 ,sir ,humphrey ,davy's safety lamp4 ,since the invention of the ,davy lamp1 a great number of modifications have been brought forward1 some of which for a short time have occupied the public attention1 but whether from increased cost or a sort of inertia that arrests improvement1 it is certain that the lamp originally devised by ,sir ,humphrey ,davy is still the favourite4 ,it was perhaps unfortunate that the lamp was called the safety lamp1 because it is not so under every circumstance that may arise1 unless it happens to be in the hands of persons who have taken the trouble to study it and understand how to correct the faults4 ,the lamp might have escaped the incessant attacks that have been made upon its just merits1 if the name had simply been that of its illustrious inventor--a ,davy lamp4 ,no one could carp at that1 whilst safety was held to mean perfect immunity from every possible and probable danger that might arise in the coal-pits4 ,the lamps are now usually placed under the charge of one man1 who trims them and ascertains that the wire gauze is in perfect order2 this latter is usually locked upon the lamp1 and as it is a penal offence1 and punishable by a heavy fine and imprisonment1 to remove the wire gauze from safety lamps in dangerous parts of the mine1 of course the miners are being gradually brought to a sense of the obligations they owe themselves and their brother-miners1 and the rash1 ignorant1 and foolhardy offences of breaking open safety lamps for more illumination1 or to light pipes1 are becoming much less frequent than formerly4 ,one of the most ingenious detector lamps is that of ,mr4 ,symons1 of ,birmingham4 7,fig4 #cfd47 ,it consisted of the old-fashioned ,davy1 but ,page #cag inside the rim of the wire gauze is placed a small extinguisher and spring1 which does not move so long as the gauze is screwed on to the lamp1 but directly the gauze is unscrewed1 the reversed movement releases the detent1 and the extinguisher falls upon the light4 ,in spite of the manifest ingenuity of this lamp1 it is not adopted1 because it costs a trifle more than the ordinary ,davy4 ,to show the remarkable perfection of the wire gauze principle1 some turpentine may be poured upon a lighted safety lamp1 when a great smoke is produced by the evaporation of the spirit1 but no flame passes through to the outside1 although the turpentine burns inside the lamp4 ,if some coarse gunpowder is laid upon two thicknesses of fine wire gauze1 it may be heated from below with the flame of the spirit lamp1 and the sulphur will gradually volatilize without setting fire to the mass of powder4 ,to show the security of the ,davy lamp1 it may be lighted and hung in a large box with glass sides1 open at the top1 and a jet of coal gas supplied at the bottom2 as this rises and diffuses in the air1 the mixture becomes explosive1 and the fact is at once evident by the alteration in the appearance of the flame of the lamp1 which enlarges1 flickers1 and frequently goes out1 in consequence of the suddenness with which the explosion of the mixture takes place inside the lamp1 producing a concussion that extinguishes the flame4 ,in this case the utility of the platinum coil is very apparent1 and it continues to glow with a red heat until the explosive character of the air in the box is changed4 ,illustration3 ,fig4 #cfd4 ,symons' self-extinguishing ,davy lamp4 ,if a large washhand-basin is first warmed by some boiling water1 which is then poured away1 and a drachm of ether thrown in1 a highly-combustible atmosphere is obtained1 and when a lighted ,davy lamp is placed into the basin so prepared1 the flame inside the lamp immediately enlarges and flickers1 but is not extinguished1 and does not communicate to the combustible vapour outside4 ,the contrast between the safety lamp and an unprotected flame is very striking2 if a lighted taper is thrust into the basin1 the ether catches fire1 and burns with a very large flame4 ,the solid conductors of heat1 which are said to enjoy this property in the highest degree1 are the metals1 marble1 stone1 slate1 and ,page #cgh other dense and compact solid substances2 whilst the opposite quality of being non-conductors1 or nearly so1 is possessed by fur1 wood1 silk1 cotton1 wool1 eider and swansdown1 paper1 sand1 charcoal1 and every substance which is of a light or porous nature4 ,the practical application of this knowledge is very apparent in the affairs of every-day life4 ,thus we rise in the morning1 and immediately after the necessary ablutions1 if it is winter time1 proceed to encase the body in non-conductors1 such as flannel and wool4 ,when we sit down to the breakfast table to make tea1 we may notice the contrivances for preventing the handle of the top of the urn1 or that of the teapot1 from becoming too hot for the fingers1 by the interposition of ivory or wood4 ,if asked to place water in the teapot from the kettle1 we instinctively seek for the well-worn kettle-holder made of ,berlin wool1 and therefore a bad conductor4 ,as we cut our meat or fish at the same meal1 we may shiver with cold1 but our fingers are not quite frozen by contact with the steel knives1 as we hold them by ivory handles2 and we are agreeably reminded that some metals are good conductors of heat1 by the pleasant warmth of the silver teaspoons1 as we stir our tea or coffee4 ,even the polish of the well-rubbed mahogany is protected from the heat of the dishes by non-conducting mats1 and plates are handed about1 if nice and hot1 with a carefully-wrapped non-conducting linen napkin4 ,supposing we prefer a bit of fresh-made toast1 the fork is provided with a non-conducting handle2 and should we peep out of window some wintry morn whilst the baker delivers his early work in the shape of hot rolls1 we notice they come out of nicely-wrapped flannel or baize1 which being a bad conductor is employed to retain their heat4 ,we read1 occasionally1 in the military intelligence1 statements respecting some newly-constructed shells which are to burst and scatter melted iron 76672 and of course the idea of the interposition of a good non-conductor of heat between the bursting charge and the molten metal must be realized in their construction4 ,the central heat of our globe is a reality that cannot be disputed1 and after digging beyond a depth of twenty feet the thermometer gradually rises at the rate of one degree of ,fahrenheit's scale for every fifteen yards4 ,the bad conducting power of the crust of the earth must1 therefore1 be apparent1 as it is easy1 knowing the diameter of our globe1 to calculate that the increase of heat downwards amounts to #aaf for each mile1 consequently at a depth of thirty and a half miles below the surface1 there will be a temperature most likely equal to #cejj1 or a heat that might easily melt cast-iron1 and would help to account for the earthquakes and eruptions of volcanoes1 which still remind us by their terrible warnings1 that we live only on the bad conducting upper crust of a globe1 the inside of which is still1 perhaps1 in a liquid and molten state4 ,monsieur ,fourier has demonstrated the non-conducting power of this shell by calculating that1 supposing the globe was wholly composed of cast-iron1 the central heat would require myriads of years to be transmitted to the surface from a depth of #aej miles2 and by inverting the process of reasoning1 we may come to the conclusion that the ,page #cgi internal heat must be excessive1 because it is confined and shut out from those influences that would carry off and weaken the intensity4 ,there are no two words1 says ,tyndal1 with which we are more familiar than matter and force4 ,the system of the universe embraces two things1 an object acted upon1 and an agent by which it is acted upon2 the object we call matter and the agent we call force4 ,matter1 in certain respects1 may be regarded as the vehicle of force2 thus1 the luminiferous ether is the vehicle or medium by which the pulsations of the sun are transmitted to our organs of vision4 ,or1 to take a plainer case1 if we set a number of billiard balls in a row1 and impart a shock to one end of the series in the direction of its length1 we know what will take place2 the last ball will fly away1 the intervening balls having served for the transmission of the shock from one end of the series to the other4 ,or we might refer to the conduction of heat4 ,if1 for example1 it be required to transmit heat from the fire to a point at some distance from the fire1 this may be effected by means of a conducting body--by a poker1 for instance2 thrusting one end of a poker into the fire1 it becomes heated1 the heat makes its way through the mass1 and finally manifests itself at the other end4 ,let us endeavour to get a distinct idea of what we here call heat2 let us first picture it to ourselves as an agent apart from the mass of the conductor1 making its way among the particles of the latter1 jumping from atom to atom1 and thus converting them into a kind of stepping stones to assist its progress4 ,it is a probable conclusion1 even had we not a single experiment to support it1 that the mode of transmission must1 in some measure1 depend upon the manner in which those little molecular stepping stones are arranged4 ,but we must not confine ourselves to the molecular theory of heat4 ,assuming the hypothesis1 which is now gaining ground1 that heat1 instead of being an agent apart from ordinary matter1 consists in a motion of the material particles2 the conclusion is equally probable that the transmission of the motion must be influenced by the manner in which the particles are arranged4 ,does experimental science furnish us with any corroboration of this inference8 ,it does4 ,more than twenty years ago ,,mm4 ,de la ,rive and ,de ,candolle proved that heat is transmitted through wood with a velocity almost twice as great along the fibre as across it4 ,this result has been recently expanded1 and it has been proved that this substance possesses three axes of calorific conduction2 the first and greatest axis being parallel to the fibre2 the second axis perpendicular to the fibre and to the ligneous layers2 while the third axis1 which marks the direction in which the greatest resistance is offered to the passage of the heat1 is perpendicular to the fibre and parallel to the layers4 ,if many solids are bad conductors of heat1 they are at all events greatly surpassed by fluids1 and especially by water4 ,the conduction of heat by that fluid is almost imperceptible1 so much so1 that it has even been questioned whether liquids do really conduct heat downwards at all4 ,it has1 however1 been found that liquid mercury will conduct heat downwards1 and therefore by analogy it may be assumed that other liquids must possess a conducting power1 although it may be exceedingly limited4 ,page #chj ,in order to prove that water is an exceeding bad conductor of heat1 a tube with a large glass bulb blown at one end is partly filled with tincture of litmus1 until it will just sink below the surface of water placed in a tall cylindrical or open jar4 ,if a copper basin1 containing burning ether1 is now floated on the top of the water1 so as to leave about a quarter of an inch between the top of the air thermometer--viz41 the bulb containing the coloured liquid--and the bottom of the copper pan1 it will be noticed that whilst the water surrounding the latter almost boils1 not the slightest effect arising from the conduction of heat can be perceived in a downward direction4 ,after the ether has burnt out of the copper vessel1 it may be removed1 and the boiling water stirred down and around the air thermometer1 when the air within it expands1 drives out the colouring liquid1 and the bulb becoming specifically lighter1 rises to the top of the containing glass4 7,fig4 #cfe47 ,illustration3 ,fig4 #cfe4 ,a ,a4 ,cylindrical glass full of water4 ,b4 ,the glass air thermometer containing the coloured liquid just standing upright1 the mouth of the tube at ,c being open4 ,d ,d is the copper basin containing the burning ether4 ,e shows how the glass bulb and tube rise after the upper basin is removed1 and the hot water comes in contact with and expands the air1 making the thermometer light1 and causing it to rise4 ,again1 if the tube of an air thermometer is placed through a cork in the neck of a gas jar1 inverted and standing on a ring stand1 and the ,page #cha jar is then filled with water1 and boiled at the top with a red-hot iron heater1 the heat does not pass downwards and affect the thermometer4 ,by introducing a syphon the water surrounding the thermometer at the bottom of the jar may be drawn off1 until the hot water is within a fraction of an inch of the air thermometer1 and still no heat is conducted1 and the liquid in the latter remains stationary4 7,fig4 #cff47 ,illustration3 ,fig4 #cff4 ,a ,a ,a4 ,inverted gas jar supported by the ring stand4 ,b4 ,the red-hot urn heater4 ,c ,c4 ,the air thermometer1 with the coloured liquid stationary at ,c4 ,d4 ,the syphon for drawing off the cold water1 and bringing the hot down close to the bulb of ,c ,c4 ,the diffusion of heat through water does not take place like that of solids1 but is effected by the motion of the particles of the water4 ,when heat is applied to the bottom of a vessel containing water1 such as an inverted glass shade1 the first effect is to expand the layer of water which is first affected by the heat2 this expanded layer being specifically lighter than the cold water above1 it rises to the upper part of the glass shade1 and its place is immediately taken by other1 colder and heavier1 water1 which in like manner moves upwards1 and is again succeeded by a fresh portion4 ,now1 the first and succeeding strata ,page #chb of water all carry off so much heat1 and thus by the convective or carrying power of the water the heat is diffused finally in the most perfect manner through the whole bulk of fluid2 and indeed1 the movement itself of the particles of water may easily be watched by putting a little paper pulp at the bottom of the inverted glass shade containing the water4 7,fig4 #cfg47 ,illustration3 ,fig4 #cfg4 ,a4 ,a4 ,inverted glass shade containing water and some paper pulp4 ,b4 ,burning spirit lamp placed under one side of the glass2 the pulp shows the rising of the heated water and the sinking of the cold1 in the direction indicated by the arrows4 ,this bad conducting power is not merely confined to water1 but is likewise apparent with oil and other fluids1 and if some water is frozen at the bottom of a long test-tube by means of a freezing mixture1 oil may then be poured upon it1 and some alcohol above the latter4 ,if the flame of a spirit-lamp is now applied to the alcohol at the top of the tube it may be entirely boiled away1 and no heat will travel down the oil and communicate with the ice1 and even after the alcohol has been evaporated away the tube can be filled up with water2 this may also be boiled1 and whilst demonstrating the bad conducting power of the oil1 the curious anomaly is observed of a vessel or tube containing ice at the bottom and boiling water at the top1 and further showing the wisdom of the ,supreme ,creator in preventing the freezing of the water of lakes1 rivers1 and seas1 by the exceptional law of the expansion of water by cold4 ,it is evident from what has been stated that liquids acquire and lose their heat by means of those currents and movements of the particles of water which have already been partly explained4 ,whatever interferes with this movement must prevent the passage of heat1 and consequently thick viscous liquids are always difficult to boil1 and in consequence of their motion being impeded they rise to too high a temperature and are burnt4 ,this fact is remarkably apparent in the manufacture of nice white lump sugar2 as the syrup is evaporated it becomes very thick1 and if boiled over a fire might frequently be burnt1 but it is boiled by the heat of steam1 and under a vacuum produced by an air-pump1 and thus the sugar-boiler is enabled to avert all danger from burning4 ,page #chc ,it is1 then1 by a continual and perpetual motion1 involving circulation of the particles1 that heat travels through water2 and the fact already described is still further elucidated by one of ,professor ,griffith's simple but telling experiments4 ,a glass tube1 about three feet in length and half an inch in diameter1 is bent as at ,a 7,fig4 #cfh71 and then being filled with water1 is suspended by a string attached to any convenient support inside a copper dish containing water1 so that the straight end is at the top of the water1 and the curved end at the bottom4 ,just before it is used some ink or other colouring matter is poured into the copper pan of water2 and it should not be added till the moment the experiment is to begin1 as any rise of temperature in the room promotes circulation1 and interferes with the colourlessness of the water in the tube1 which is compared with the inky fluid in the basin4 ,directly heat is applied the hot water rises to the top of the copper vessel1 and thence gradually up the tube2 and this movement is rendered visible by the hot coloured liquid matter creeping slowly up the tube1 and displacing the colourless water1 which falls gradually into the copper pan4 7,fig4 #cfh47 ,illustration3 ,fig4 #cfh4 ,a4 ,the bent glass tube full of water4 ,b ,b4 ,the copper pan containing coloured water4 ,the arrows show the circulation of the water4 ,the principle of the circulation of the particles of water being once understood1 it is easy to comprehend how it is applied to the heating of buildings by what is called the ,hot ,water ,apparatus4 ,a coil of pipe is enclosed in a proper furnace1 and the bottom end communicates with a pipe coming from a second tube or set of coils1 placed above it in another apartment1 whilst the top of the latter coil communicates with the top pipe of the first coil4 ,when the fire is lighted1 the circulation through the first coil of pipe commences1 and is communicated to the second1 and from that back again to the first2 so that the hot water system ,page #chd involves an endless chain of pipes of water1 provided with proper safety valves to allow for the escape of any expanded air or steam2 and serious accidents have occurred in consequence of persons neglecting to look after the perfection of this safety valve4 ,the fearful accident which occurred to the hot water casing around one of the funnels of the ,great ,eastern offers a painful but memorable example of the heating of water1 and of the dangers that must arise if the pipe1 casing1 or other vessel which contains it1 is not provided with an escape or safety valve1 which must always be in good working order4 ,mr4 ,jacob ,perkins1 in #ahbd1 made his name remarkable for experiments with the circulation of water through tubes1 and his account of the invention and improvement of the ,steam ,gun1 in which the improvement consists chiefly in the circulation of water through coils of pipe1 is so important that we give it verbatim1 with a drawing of the steam gun2 and the author is enabled to vouch for the accuracy of the statements made in the description of the apparatus1 as he purchased one of the improved steam guns1 and exhibited it at the ,polytechnic ,institution1 where it discharged three hundred bullets per minute4 ,illustration3 ,fig4 #cfi4 ,the charging tube and gun-barrel of steam gun4 ,the expansive power of steam has often been proposed as a substitute for gunpowder1 for discharging balls and other projectiles2 the great danger1 however1 which was formerly thought to be inseparably connected with the generation and use of steam1 at so extraordinary a pressure as appeared necessary to produce an effect approximating to that of gunpowder1 prevented scientific men from testing the power of this new agent by experiment4 ,it was also apparent that the apparatus which was ordinarily used for generating steam for steam-engines was wholly inadequate to sustain the necessary pressure1 and that one ,page #che of a totally different character must be contrived before steam could be sufficiently confined to come into competition with its powerful rival4 ,in the year #ahbd1 ,mr4 ,jacob ,perkins succeeded in constructing a generator of such form and strength1 as allowed him to carry on his experiments with highly elastic steam without danger1 although subjected to a pressure of #ajj atmospheres4 ,the principle of its safety consisted in subdividing the vessel containing the water and steam into chambers or compartments1 so small1 that the bursting of one of them was perfectly harmless in its effects1 and only served as an outlet1 or safety valve1 to relieve the rest4 ,although ,mr4 ,perkins' generator was originally intended for working steam engines 7it having long been evident to him that highly elastic steam used expansively would be attended with considerable economy71 the idea occurred to him1 in the course of his experiments1 that he had already solved the problem of safely generating steam of sufficient power for the purposes of steam gunnery2 and that the steam which daily worked his engine possessed an elastic force quite adequate to the projection of musket balls4 ,he therefore caused a gun to be immediately constructed1 and connected by a pipe to the generator1 the first trial of which fully realized his most sanguine anticipations4 ,its performance1 indeed1 was so extraordinary and unexpected1 that it gave rise to a paradox1 which was difficult of explanation--viz41 that steam1 at a pressure of only forty atmospheres1 produced an effect equal to gunpowder2 whereas it was known that the combustion of gunpowder was attended with a pressure of from #ejj to #ajjj atmospheres4 ,mr4 ,perkins gives the following explanation of this apparent discrepancy1 by referring to the small effect produced by fulminating powder1 compared to gunpowder1 although many times more powerful2 he supposes that the action of fulminating powder1 however intense1 does not continue sufficiently long to impart to the ball its full power4 ,the explosion of gunpowder1 although not so powerful at the instant of ignition1 is nevertheless1 in the aggregate1 productive of greater effect than that of fulminating powder1 because the subsequent expansion continues in action upon the ball 7but with decreasing effect71 until it has left the barrel4 ,the action of steam differs from either of these agents1 inasmuch as it continues in full force until the ball has left the barrel2 and to this is assigned the cause of its superiority4 ,in the year #ahbf1 ,mr4 ,perkins had so perfected the mechanism of the gun and generator that1 at an exhibition and trial of its power1 in the presence of the ,duke of ,wellington and other distinguished officers of the ,ordnance ,department1 balls of an ounce weight were propelled1 at the distance of thirty-five yards1 through an iron plate one-fourth of an inch in thickness2 also1 through eleven hard planks1 one inch in thickness1 placed at distances of an inch from each other4 ,continuous showers of balls were also projected with such rapidity1 that when the barrel of the gun was slowly swept round in a horizontal direction1 a plank1 twelve feet in length1 was so completely perforated1 that the line of holes nearly resembled a groove cut from one of its ends to the other4 ,page #chf ,illustration3 ,fig4 #cgj4 ,perkins's steam gun4 ,page #chg ,a is an iron furnace1 containing a continuous coil of iron tubing1 #hj feet in length1 #a inch of external and #e_/hth inch of internal diameter1 within which the fire is made2 the upper end of this tube1 ,b1 called the flow-pipe1 is extended any required distance to the top of the generator4 ,the furnace is provided with a very ingenious heat governor or regulator1 by which the intensity of the fire is always proportionate to the temperature which it may be requisite to maintain in the tubes4 ,h is an iron box1 containing a series of levers1 b b b2 c1 a nut screwed upon the flow-pipe1 and in contact with the short arm of the lowest of the levers4 ,e4 ,a lever1 from one end of which is suspended the damper f1 and from the other end the rod g1 which rests upon the long arm of the highest of the levers1 b b b4 ,when the apparatus has arrived at the required temperature1 the nut c is screwed down until it bears upon the lever4 ,any farther increase of temperature will expand or lengthen the flow-pipe1 and depress the short arm of the lever1 which is in contact with the nut4 ,the combined and multiplied action of the levers will then elevate the rod g1 and the damper f will descend to check the draught4 ,when the fire slackens1 and the apparatus cools1 the action of the levers will be reversed1 and the damper will open4 ,the space through which the damper moves1 compared with the nut c1 is as #bjj to #a4 ,c is the generator1 composed of a strong iron tube1 #c inches diameter and #f feet in length1 within which are eight smaller tubes1 having their ends welded to the ends of the larger tube4 ,these small tubes communicate at the top with the flow-pipe ,b1 and at the bottom with the return-pipe ,d1 which is continued to the bottom of the furnace-coil of tubing4 ,the circulation in the tubes is occasioned by the difference in the specific gravities of the water composing the ascending and descending currents2 the portion contained in the flow-pipe and fire coil becoming expanded by the heat1 ascends by its superior levity2 while that contained in the small tubes of the generator1 having given off its heat1 acquires increased density1 and descends through the return-pipe ,d to the bottom of the furnace-coil1 to take the place of the ascending current4 ,when the hot-water current has arrived at a temperature of #bab and upwards1 cold water is injected into the generator1 and becomes converted into steam by its contact with the small tubes2 the rapidity of evaporation and the pressure of the steam depending1 of course1 upon the temperature of the hot-water current1 which at #ejj will cause a pressure within the tubes of #ej atmospheres1 or #gej lbs4 upon the square inch4 ,the whole apparatus is proved to be capable of sustaining a pressure of #bjj atmospheres1 or #cjjj lbs4 upon the square inch4 ,g4 ,a force pump for injecting water into the generator4 ,i4 ,the indicator for exhibiting the pressure of the steam in the generator1 and of the water in the boiler2 it may be connected with either by means of the valves attached to the levers4 ,j4 ,valve to regulate the pressure of water4 ,j #a4 ,valve to regulate the pressure of steam4 ,k4 ,the steam pipe4 ,l4 ,the gun4 ,m4 ,the discharging lever acting upon the valve ,n4 ,o4 ,the discharging cock1 by a simple adjustment in which balls are transferred from the charging tube ,p to the gun barrel1 singly or in a continuous shower4 ,as the perfection and introduction of the steam gun was not a field for private enterprise1 and the ,british ,government having declined to institute experiments at its own expense1 ,mr4 ,perkins was reluctantly compelled to leave the project1 and to engage in others of a more lucrative1 although1 perhaps1 of a less important nature4 ,he did not suspend his operations1 however1 until he had constructed for the ,french ,government a piece of artillery which discharged balls weighing five pounds at the rate of sixty per minute4 ,the gun and generator exhibited at the ,polytechnic ,institution during the time that ,mr4 ,pepper was the ,resident ,director were the production of ,mr4 ,a4 ,m4 ,perkins1 of ,london1 who has invented an entirely new method of generating steam1 which has been successfully applied to steam engines1 and is at once so simple1 safe1 and economical1 as to leave little doubt that1 with its aid1 the steam gun will ere long rank amongst the first instruments of warfare4 ,page #chh ,the gun1 except in a few minor mechanical details1 does not differ from that originally constructed by ,mr4 ,jacob ,perkins4 ,the novelty which distinguishes the generator from all others1 consists in the manner of conveying the heat from the fire to the water1 without exposing the generator to the action of the fire4 ,this is accomplished by means of the circulation1 in iron tubes1 of a current of hot water1 which is entirely separate from1 and independent of1 that to be evaporated in the generator4 ,the following are the principal advantages which this generator possesses over all others3 ,freedom from all wear or deterioration consequent upon exposure to the fire1 an important quality in a generator that is to be subjected to great pressure1 inasmuch as its original strength remains unimpaired2 no accident can arise from want of water in the generator1 and the precautions indispensably requisite when a generator is in contact with the fire are quite unnecessary1 as the water may be drawn off with impunity without producing the least injurious effect1 and the grossest neglect is followed by no worse consequences than an inefficient supply of steam2 an explosion of the generator is impossible1 as the temperature of the furnace-coil always exceeds that of any other part of the apparatus1 and consequently1 being the weakest part1 is invariably the first to yield when the pressure is carried beyond the strength of the pipes2 economy of fuel is also obtained1 with a small amount of fire surface4 ,the circulation of the water has likewise the effect of preserving the fire-coil from the decay to which boilers are liable2 many such coils1 which have been in constant use for eight years1 being apparently as good as when first erected4 ,the whole apparatus is exceedingly simple1 and will be readily understood by reference to the accompanying diagram4 7,fig4 #cgj47 ,the steam has often been raised to a pressure of #gjj lbs4 on the square inch1 but one-third of that pressure is sufficient to completely flatten the balls when discharged against an iron target one hundred feet distant from the gun2 and a pressure of #djj lbs4 per square inch1 at the same distance1 shivers the ball to atoms1 with the production in a dark room of a visible flash of light4 ,steam guns are generally mounted upon a ball and socket joint1 which allows the barrel to move freely in every direction4 99 99 99 99 99 ,the conduction of heat through gases is also very slow when heat is applied to the upper part of any stratum of air4 ,heat appears to be diffused through air only by the circulation and rising of the heated and lighter strata1 and the sinking of the colder currents which take their places2 hence the danger of sitting in a room under an open skylight4 ,a current of cold air may descend upon the head of the individual1 whilst the warmer air takes some other opening to escape from4 ,no doubt the movement of heated volumes of air is subject to definite laws1 which apply themselves under every case1 but are rather difficult to grasp when the subject of ventilation is concerned4 ,the philosophical ventilator is often dreadfully teased by the inversion of all that he had ,page #chi planned1 or the total failure of his apparatus4 ,no specific mode of ventilation can be found to suit all rooms and buildings2 they are like the patients of a physician who cannot be cured by one medicine only1 but must have a treatment adapted properly to each case4 ,if the fires1 candles1 gas1 or oil-lamps1 doors1 windows1 and chimneys1 were always under the control of the scientific ventilator1 his task would be very simple1 but it is well understood that a ventilating system which answers well if certain doors communicating with lobbies are closed1 fails directly they are accidentally opened4 ,the watchful care of the ventilator must begin with the lowest area door1 and in his calculations he must study the effect of every other door or window that may be opened1 so that if a scientific man undertakes to ventilate a house1 he must have a well-drawn plan hung up in the hall1 and it must be clearly understood by the inmates that any interference with that plan will prejudice the whole4 ,there are a few common principles which will guide in ventilation1 and these are1 first1 the rise of hot and the fall of cold air2 second1 that if an aperture is provided at the top of a room for the escape of hot air1 an equally large aperture must be left for the entry of cold air2 third1 the aperture for the escape of hot air must be adapted in size to the number of persons likely to enter the room1 and the number of gas or other lights burning in it4 ,during the daytime1 moderate apertures for the exit and entrance of air may suffice1 but these must be largely increased at night1 when the room is filled with people and lighted up4 ,expanding and contracting openings are therefore desirable1 and they are to be regulated by rules stated on the plan of the ventilating system 7already alluded to as being hung up in the hall7 of the house which has submitted itself to a perfect system of ventilation1 and no hall-keeper1 footman1 or butler should be allowed to remain in his post unless he undertakes to comprehend the system and work it properly by the written rules4 ,dr4 ,angus ,smith1 in a very able paper ,on the ,air of ,towns1 says--,one of the conditions of health1 and a most important1 if not the most important of all1 is to be found in the state of the atmosphere4 ,as to the effect on the inhabitants1 the question becomes exceedingly complicated2 but the ,registrar-,general's returns are an unanswerable reply as to the results of the lethal influences of the district4 ,few people seem clearly to picture to themselves the meaning of a decimal plan in the percentage of death1 and few clearly see that there are districts of ,england where the deaths at least in some years1 and when no recognised epidemic occurs1 are three times greater than in others4 ,when we hear of the annual deaths in some districts being #c4d per cent41 and in the whole of ,england #b4b1 it is simply that #cd die instead of #bb1 whilst even that is too slightly stated1 as the whole of ,england would show a lower death-rate if the towns were not used to swell it4 ,this quotation is given here to remind our readers of the important question of a supply of pure air as well as pure water and pure food2 and if the agricultural labourer1 with all his exposure to variable ,page #cij weather1 can take the first place in the scale of mortality1 and outlive the members of all other trades and professions1 it is evident that the importance of pure air is not overrated4 ,every effort ought1 therefore1 to be made in large schools1 hospitals1 and barracks1 to enforce a rigid system of supply of fresh air1 and a sewage or removal of the impure2 and in the use of a certain test employed by ,dr4 ,smith for the detection of organic matter in the air a number of approximations were obtained1 which clearly demonstrated that #a grain of organic matter was detected in #gb1jjj cubic inches of air in a room1 and the same quantity in #hjjj cubic inches taken from a crowded railway carriage4 ,illustration3 ,fig4 #cga4 ,a ,b4 ,the glass tube4 ,c4 ,the spirit lamp1 with a very large wick2 if a little ether is mixed with the spirit in the lamp it increases the length of the flame4 ,d4 ,the effect of the ascension of air1 increased by warming the top of the tube with the lamp ,d4 ,to show the rising of heated air1 a long glass tube1 about three-quarters of an inch in diameter1 may be provided and held over the flame of a spirit lamp at an angle of sixty degrees4 ,as the tube warms1 the heated air rushes past the flame with great rapidity1 and pulls it out or elongates it so much1 that the sharp point of the spirit-flame ,page #cia will frequently be seen at the end of a tube ten feet six inches in length4 ,the flame is1 as it were1 the sign-post that indicates the path or direction of the air4 7,fig4 #cga47 ,upon the like principle1 heated air may be dragged down the short arm of a syphon1 provided the other arm is sufficiently long to impart a strong directive tendency to the upward current1 and this mode of setting air in motion has been frequently proposed in numerous schemes for ventilation4 ,in order to prove the fact that an inverted syphon will act in this manner1 an iron pipe of three inches diameter and six feet long may be bent round during the construction into the form of a syphon1 so that the short length is about one foot long1 and the long length the remaining four feet1 allowing one foot for the bend4 ,if the interior of the long arm is first warmed by burning in it a little spirits of wine from a piece of cotton or tow wetted with the latter 7which can be easily done by dropping in such a wetted piece into the bend of tube1 so that it is just under the opening of the long part of the tube71 the air is soon set in motion up the long pipe1 and as it must be supplied with fresh volumes of air to take the place of that which rises1 and as the only entrance for the fresh air can be down the short arm of the syphon1 the circulation soon commences1 and it proceeds as long as the upper arm is kept sufficiently warm4 ,if a flame is held over the mouth of the short arm1 it is immediately dragged downward1 whilst1 if held at the mouth of the long pipe1 the motion of the air is seen by the assistance of the flame to be in the contrary direction4 7,fig4 #cgb47 ,illustration3 ,fig4 #cgb4 ,a ,b4 ,inverted sheet iron syphon4 ,at ,c is seen the piece of tow moistened with alcohol1 which1 being set on fire1 warms the tube ,b4 ,d4 ,a lighted torch of coloured spirit1 the flame of which is dragged down the tube at ,a by the descending current1 and is impelled upwards by the ascending current ,b4 ,this plan of ventilation was proposed to be used in rooms in connexion with the chimney and chimney-piece1 and in order to give it an ornamental appearance1 the chimney-piece was supplied with two ornamental hollow columns1 the ends of which were open at the mantel-shelf1 and the tubes or columns were continued under the hearthstone1 proceeding up the back of the grate and entering the chimney1 in which there would be a constant current of heated air1 and it was expected that the ,page #cib syphon arrangement would keep a current of air always in motion1 and thus help to ventilate the room4 7,fig4 #cgc47 ,this plan1 however1 does not appear to have been adopted1 and wisely so1 because half the time the syphon arrangement might invert itself1 and vomit smoky air out of the chimney into the room2 indeed it is surprising what odd and contradictory freaks are performed by currents of air4 ,the author remembers a case where two rooms on the same floor1 the one a dining-room and the other a drawing-room1 were always exhibiting the most absurd phenomena of smoke4 ,if the fire in one room was lit1 then the other1 in a few moments1 began to smell exactly like the inside of a gas manufactory1 and was1 of course1 more or less filled with smoke1 whilst the room in which the fire was actually burning remained quite free from this annoyance4 ,the smoke appeared to issue from the wainscot or moulding which runs round at the bottom of the wall1 and was at first thought to be an escape from the chimney of the kitchen beneath1 the inside of which was duly examined and thoroughly stopped with cement in every place likely to afford a channel to the smoke1 and ,page #cic the crevice whence the smoke issued was also filled in neatly with cement4 ,but it was all in vain2 the smoke then made its way out from another part of the cornice1 and at last the rooms exhibited a beautiful reciprocating action4 ,if the drawing-room fire was lighted the dining-room was full of smoke1 and if the latter was lighted the former had the agreeable visitation4 ,at last the backs of the two grates were examined1 and in each was discovered a hole about one inch in diameter2 and it was also found that the spaces at the back of the stoves had not been filled in properly1 and1 indeed1 communicated with the hollow space behind the cornice4 ,when1 therefore1 the fire was lighted1 and coals heaped on just above the hole1 the gas and smoke distilled through the orifice and travelled on1 where it found the most convenient exit2 and the fact is sadly at variance 7apparently7 with theory1 because it might be considered that cold air would rush towards a fire1 and that the draught ought to have been from the cornice to the chimney instead of vice vers4 ,the fact seems to be that the coal in all grates is1 in the act of burning1 distilling and giving off inflammable gas2 when the coal was1 therefore1 heaped above the orifice1 and was1 possibly1 caked hard at the top1 the gas distilling from it escaped more easily from the little orifice than elsewhere1 and chance determined that the channel or delivery pipe should be in the direction of the drawing-room when the fire was burning in the dining-room1 and in the contrary direction when the fire was lighted in the latter chamber4 ,the nuisance was stopped by plugging the holes at the back of the grate with clay1 and putting a sheet of iron over the orifice4 ,illustration3 ,fig4 #cgc4 ,a ,b4 ,chimney-piece supported on two hollow ornamental pillars corresponding with the short arm of a syphon4 ,c ,c ,c4 ,the dotted line showing the pipes leading from each pillar under the hearth1 and terminating in a long pipe passing into the chimney4 ,the arrows show the path of the air descending from the chimney-piece and ascending in the chimney4 ,before ,dr4 ,faraday was appointed as a scientific counsellor to assist the deliberations of the ,trinity ,board in connexion with lighthouses1 all the lamps were burnt in the lanterns with the smallest and most imperfect arrangement for carrying off the heated air and products of combustion2 as a natural consequence1 and particularly on cold nights1 the windows of the lantern of the lighthouse were covered with ice derived from the condensation of the water produced by the combustion of the hydrogen of the oil1 whilst the carbon generated such quantities of carbonic acid that the light-keepers were unable to stay in the lantern1 and if obliged to visit the latter 7whilst looking to improving the light of any single lamp that might be burning dimly71 they were almost overpowered with the excess of carbonic acid1 and stated1 in their evidence1 that it produced headache and sickness1 and a tendency to insensibility4 ,faraday immediately established a system of ventilation2 and by attaching a copper tube to the top of each lamp-chimney1 and centering them all in one large funnel passing to the top of the lighthouse1 the whole of the water which previously condensed on the glass windows and impeded the light1 besides injuring the brass and copper fittings1 was carried off1 as also the poisonous carbonic acid gas2 and thus1 as ,dr4 ,faraday expressed himself1 a complete system of sewage was applied to the lamps of the lighthouses4 ,if any one of the numerous stories of ships saved by the ,eddystone ,lighthouse could demonstrate more than another the value of this beacon ,page #cid in mid ocean1 it must be the graphic account in the ,times of the gallant conduct of the ,british ,admiral with his fleet whilst breasting the frightful storm of ,october1 #ahei1 and endeavouring to reach ,plymouth ,sound3-- ,it was on ,saturday1 the #bbnd ,october1 that the ,hero1 the ,trafalgar1 the ,algiers1 and the ,aboukir1 accompanied by the ,mersey1 the ,emerald1 and the ,melpomene1 put to sea from ,queenstown4 ,up to the afternoon of ,monday the squadron met with no remarkable adventure1 but about that time1 just after the crews had been exercised at gunnery practice1 heavy storms of hail and sleet began to set in4 ,still there was no immediate indication of the tempest at hand1 and at sunset topsails were double-reefed and courses reefed for the night1 with no particular character about the wind1 except that of extreme variability4 ,as the morning broke on ,tuesday--the day of the storm--the ,land's-end was sighted1 and the rain and the wind continued to increase4 ,about nine ,a4,m4 the advent of the gale was no longer doubtful2 topgallantyards were sent on deck and topgallantmasts struck1 and the signal was given from the flagship1 ',form two columns2 form line of battle2 ,admiral will endeavour to go to ,plymouth4' ,to ,plymouth1 accordingly1 the course of the fleet was shaped1 but so terrifically had the wind increased that it became very questionable whether the sternmost ships of the line could possibly succeed in entering the ,sound4 ,upon this the ,admiral determined to wear the fleet together1 stand off1 and face the storm1 a manoeuvre which1 under circumstances of great difficulty1 was most gallantly executed4 ,the ships were close upon the ,eddystone ,lighthouse1 round which they 'darted like dolphins' under the tremendous pressure of the gale1 the ,trafalgar stopping in the midst of the storm to pick up a man who had fallen overboard4 ,the whole squadron now stood off the land1 the ,mersey and ,melpomene furling their sails1 and the former vessel steaming along 'like an ocean giant4' ,still the gale increased till about three ,p4,m41 when there occurred that remarkable phenomenon by which these rotatory tempests are characterized4 ,the fleet had got into the very centre of the storm1 the 'eye' of the tornado1 and1 though the sea towered up and broke in tremendous billows all around1 the wind suddenly ceased and the sun shone4 ,when1 however1 the signal had been given and obeyed for setting sail again1 the ships soon encountered the gale once more--not1 as before1 from the ,s4,e41 but the ,n4,w4--and in greater force than ever4 ,it was now a perfect hurricane2 and for three hours the whole fury of the tempest was poured upon the squadron4 ,when it began1 at length1 to abate a little1 the four line-of-battle ships and one of the frigates were still in company1 and all doing well4 ,the ,mersey and the ,emerald had steamed into ,plymouth1 but the five remaining vessels kept in open order throughout that terrible night1 wore in succession by night signal at about one ,a4,m41 made the land at daylight1 formed line of battle1 came grandly up ,channel under sail at the rate of eleven knots an hour1 steamed into ,portland1 and 'took up their anchorage without the loss of a sail1 a spar1 or a ropeyarn4' ,after making the important improvement in the ventilation of lighthouses1 many letters were addressed to the learned philosopher by ,page #cie numerous light-keepers1 one of which in plain but striking language related that the enemy 7alluding to the water and carbonic acid7 was now driven out4 ,illustration3 ,the ,british fleet rounding the ,eddystone ,lighthouse during the great storm of ,october1 #ahei4 p4 #cid ,the ingenious invention alluded to was succeeded by another and equally simple but philosophical arrangement1 which ,dr4 ,faraday presented to his brother1 and it was duly patented4 ,it consisted of an arrangement for ventilating gas burners1 and it must be obvious that a necessity exists for such ventilation1 because every cubic foot of coal gas when burnt produces a little more than a cubic foot of carbonic acid4 ,a pound weight of ordinary coal gas contains about #c_/ajths of its weight of hydrogen1 which when burnt produces two pounds and #g_/ajths of a pound of water4 ,a pound of ordinary coal gas also contains about #g_/ajths of its weight of charcoal1 which produces when burnt rather more than two and a half pounds of carbonic acid gas--viz41 #b4ef4 ,in order to burn this quantity of gas nineteen cubic feet and #c_/ajths of a foot of atmospheric air1 containing #d4bf cubic feet of oxygen1 are required4 ,illustration3 ,fig4 #cgd4 ,a ,b4 ,gas pipe and argand burner2 the air enters1 as usual1 up the centre of the argand4 ,c ,c4 ,the first glass chimney open at the top4 ,d ,d4 ,the second glass chimney closed at the top1 with a disc of double talc1 and fitting over ,c ,c1 and leaving a space between the two glasses1 down which the air passes1 and into the ventilating tube1 ,e ,e4 ,h ,h4 ,the ground-glass globe closed at the top1 and surrounding the whole4,i ,footnote ,i3 ,mr4 ,faraday1 of ,wardour-street1 supplies this ventilating lamp4 ,it is not therefore surprising that as common coal gas is sometimes purified carelessly1 and contains a minute trace of sulphuretted hydrogen1 with some bisulphide of carbon vapour1 that it should produce the most prejudicial effects in badly ventilated rooms1 and especially in some of those perched up glass boxes in large places of business1 where clerks are obliged to sit for many consecutive hours1 lighted by gas1 and breathing their own breath and the products of combustion from the gas light1 thereby rendering themselves liable to diseases of the lungs1 and also to very troublesome throat attacks1 when leaving their close glass boxes1 and passing into the cold night air4 ,the dangerous product of the combustion of ordinary coal gas is sulphurous acid--viz41 ,page #cif the same gas as that generated when a sulphur match is burnt2 and if it will attack the bindings of books1 and damage furniture1 goods in shops1 curtains1 c41 in consequence of the large quantity of water with which it is accompanied1 how much more is it not likely to injure the delicate organism of the breathing apparatus of the lungs8 ,dr4 ,faraday's lamp is therefore a great boon1 but1 like a great many other clever things1 it must be adapted to the currents of air and draught from the room2 and means must be taken to prevent the draught becoming too powerful in ,faraday's lamp1 or else the illuminating power is destroyed by the thorough combustion of the carbon of the coal gas1 and the heat generated is so intense that the glasses soon crack1 and of course become useless4 ,the lamp will answer very well if 7as has been already stated7 the draught in the ventilating pipe is not too great4 ,illustration3 ,fig4 #cge4 ,section showing the two air-shafts4 ,a4 ,the downcast4 ,b4 ,the upcast4 ,c ,c4 ,one of the working galleries in connexion with the upcast and downcast4 ,d4 ,the furnace at the bottom of the upcast4 ,in this sketch one gallery only has been shown1 to prevent confusion and to show the principle4 ,the system already explained and illustrated is likewise carried out on a much larger scale in the ventilation of coal pits1 where a shaft is usually sunk into the ground for the admission of air1 which1 after circulating through the intricate windings and mazes of the coal pit workings1 escapes at last from another shaft1 at the bottom of which is placed a powerful furnace1 and this is kept burning night and day1 so ,page #cig that the movement of the air is maintained in one direction--viz41 from the outer air down the shaft called the downcast1 thence to the galleries1 where the coal hewers are working1 to the second shaft1 near which the furnace is placed1 and up this latter the air travels2 the shaft1 pit1 or funnel being very appropriately termed the upcast4 ,should the furnace at the bottom of the upcast be neglected1 the ventilation may be just balanced1 or set slightly towards the downcast2 under these circumstances the carbonic acid from the fire will begin to circulate in the galleries1 and poison those who are not aware of its presence and take the proper means to escape4 ,such accidents1 amongst the host of others that occur in a coal pit1 have actually been recorded2 and the firemen1 whose duty it might be to attend to the proper burning of the furnace1 have had to pay the penalty of death for their own carelessness in falling asleep and neglecting to maintain the ventilation of the mine in one direction4 7,fig4 #cge47 ,these details are amply sufficient to demonstrate the manner in which heat is diffused through air1 whilst the rarefication of the air by heat suggests the cause of those frightful storms of wind that rush from other and colder parts of the surface of the globe1 to supply the void produced by the cooling and contraction of the enormous volumes of gaseous matter4 ,the ,radiation of ,heat4 ,when rays of heat are emitted from incandescent matter1 they are not necessarily visible1 nay1 they are generally invisible1 and not accompanied with a manifestation of light1 and pass with great velocity through a void or vacuum1 also through air and certain other bodies4 ,from what has been stated respecting the manner in which air1 by continually moving1 and by convection1 carries off heat1 it might be thought that no proof existed that invisible rays of heat are really thrown off from a ball filled with boiling water4 ,but this question is set at rest by the fact1 that such a ball will cool rapidly when suspended by a string inside the receiver of an air pump from which the atmospheric air has been removed1 so that no conduction of the particles of air could possibly remove the heat4 ,in the year #aghf1 ,colonel ,sir ,b4 ,thompson examined the relative conducting powers of air and a ,torricellian vacuum--the latter being used because1 as the experimenter stated1 it was impossible to obtain a perfect vacuum1 on account of the moist vapour which exhaled from the wet leather and the oil used in the machine1 for at that time carefully ground brass plates were not used in air-pumps1 but plates only1 with a circular piece of wet leather upon them4 ,in a paper which ,colonel ,sir ,b4 ,thompson read before the ,royal ,society1 he stated that ,it appears that the ,torricellian vacuum1 which affords so ready a passage to the electric fluid1 so far from being a good conductor of heat1 is a much worse one than common air1 which of itself is reckoned among the worst2 for when the bulb of the thermometer was surrounded with air1 and the instrument was plunged into boiling water1 the mercury rose from #ah to #bg ,page #cih in forty-five seconds2 but in the former experiment1 when it was surrounded by a ,torricellian vacuum1 it required to remain in the boiling water one minute thirty seconds to acquire that degree of heat4 ,in the vacuum it required five minutes to rise to #dh-b_/ajths2 but in air it rose to that height in two minutes forty seconds2 and the proportion of the times in the other observation was nearly the same4 ,it appears1 from other experiments1 that the conducting power of air to that of the ,torricellian vacuum1 under the circumstances described1 is as #ajjj to #gjb nearly1 for the quantities of heat communicated being equal1 the intensity of the communication is as the times inversely4 ,by others it appears that the conducting power of air is to that of the ,torricellian vacuum as #ajjj to #fjc4 ,illustration3 ,fig4 #cgf4 ,the air-pump and receiver1 containing at ,a the electric light in the focus of a concave mirror1 and at ,b a delicate thermometer1 also in the focus of a concave mirror4 ,it is therefore very interesting to discover that the attention of experimentalists was early directed to the fact that heat was independent of the air1 and passed either as waves of heat or molecules of heat through space4 ,the velocity with which heat moves through a vacuum is very great1 and in an experiment performed by ,m4 ,pictet1 no perceptible interval took place between the time at which caloric quitted a heated body and its reception by a thermometer at a distance of sixty-nine feet4 ,it appears also1 from the experiments of the same philosopher1 to be thrown off or radiated in every direction1 and not to be diverted 7as shown at p4 #cfi7 by any strong current of air passing it transversely4 ,sir ,humphrey ,davy ignited the charcoal points connected with a battery in a vacuum1 taking care to place the charcoal points at the top of the jar1 and a concave mirror1 with a delicate thermometer in its focus1 at the bottom of the vessel placed upon the air-pump plate4 ,the effect of radiation was ,page #cii ascertained first when the receiver was full of air1 and next when it was exhausted to #a_/abjth 7i4e41 #aii parts pumped out1 leaving only one part of air in the receiver74 ,in the latter case1 the effect of radiation was found to be three times greater than in an atmosphere of the common density4 ,the greater rise of the thermometer in vacuo than in air is to be ascribed to the conducting power of the latter2 for this conducting power1 by reducing the temperature of the heated body1 has a constant tendency to diminish the activity of radiation1 which is always proportional to the excess of the temperature of the heated body above that of the surrounding medium4 7,fig4 #cgf47 ,count ,rumford's experiments with a ,torricellian vacuum gives the proportion of five in vacuo to three in air for the quantities of heat lost by radiation1 and by conduction or diffusion4 ,it is not1 perhaps1 departing very far from the truth1 if it be stated that one half of the heat lost by a heated body escapes by radiation1 and that the rest is carried off by the convective power of currents of air4 ,illustration3 ,fig4 #cgg4 ,negretti and ,zambra's terrestrial radiation thermometer4 ,the bulb of this instrument is transparent1 and the divisions engraved on its glass stem4 ,in use it is placed with its bulb fully exposed to the sky1 resting on grass1 with its stem supported by little forks of wood1 and protected from the wind4 ,if the process of radiation was not constantly proceeding1 it can easily be imagined that the temperature of our globe would become so elevated by the regular accession of heat from the sun's rays1 that the vegetation would be parched up and destroyed1 and consequently all animals and the human race must become extinct4 ,the best time to notice the radiation of heat from the earth is at night and after a hot summer's day4 ,if the sky is clear1 it will be noticed 7with the help of a thermometer17 that the ground is several degrees colder than the air a few feet above it4 7,fig4 #cgg47 ,it is this reduced temperature that causes the deposition of dew1 and produces the earth-cloud which so nearly resembles a sheet of water as to have been occasionally mistaken for an inundation1 the occurrence of the previous night4 ,mr4 ,luke ,howard has called this cloud1 which is the lowest form of these draperies of the sky1 ,the ,stratus1 or evening mist2 but when permanent1 and increased to a depth so as to rise above our heads1 it is then called the morning fog1 so peculiarly agreeable in ,london when incorporated with the black smoke1 making a fine reddish-yellow ochreous mist4 ,by placing a thermometer1 standing at the ordinary temperature of the air1 cased ,page #djj with a good radiating material1 such as filaments of cotton1 in the focus of a concave mirror1 and by turning this arrangement towards a clear sky in the evening1 it will be noticed that the temperature falls several degrees4 ,good radiators of heat are black and scratched surfaces1 filaments of cotton1 grass1 twigs1 boughs1 and certain leaves1 especially those with a rough surface4 ,bad radiators of heat are bright and polished metallic surfaces1 white woollen cloth or flannel1 hard and dense substances1 such as a gravel path and stone1 or those leaves which have a polished surface1 such as the common laurel4 ,it is the frozen dew and mist which produce the beautiful effect of hoar-frost and icicles on the trees and bushes1 the primary cause being the radiation of heat from the various objects on the surface of the earth1 as well as from the latter itself4 ,when the wind is high1 dew does not deposit1 as it is necessary that the air should be calm1 in order to receive the cooling impression of the cold earth1 and to deposit the moisture1 which it holds in solution as invisible steam4 ,when the wind blows1 it mixes all parts of the air together1 and prevents that difference of temperature which causes the deposit of dew4 ,hence the evening mist will be more generally observed in the bosom of a valley surrounded by hills and screened from the winds that may blow from either quarter4 ,the continual presence of moisture in the air is well shown by the condensation of water on the outside of a glass of cold spring water1 or especially on the outside of a jug containing iced water4 ,the invisible steam is always ready to bathe the tender plants with dew1 which would otherwise perish and be burnt up during a hot summer1 if they did not radiate heat at night1 and thus condense water upon themselves4 ,the presence of watery vapour in the air becomes therefore a matter of great importance1 and hence the construction of hygrometers or measurers of the moisture in the air4 ,regnault's condenser hygrometer consists of a tube made of silver1 very thin1 and perfectly polished2 the tube is larger at one end than the other1 the large part being #a4h in depth by #h4aj in diameter4 ,this is fitted tightly to a brass stand1 with a telescopic arrangement for adjusting when making an observation4 ,the tube has a small lateral tubulure1 to which is attached an ,india-rubber tube with ivory mouthpiece2 this tubulure enters at right angles near the top1 and traverses it to the bottom of largest part4 ,a delicate thermometer is inserted in through a cork1 or ,india-rubber washer1 at the open end of the tube1 the bulb of which descends to the centre of its largest part4 ,a thermometer is attached for taking the temperature of the air2 also a bottle for containing ether4 ,to use the condenser hygrometer1 a sufficient quantity of sulphuric ether is poured into the silver tube to cover the thermometer bulb4 ,on allowing air to pass bubble by bubble through the ether1 by breathing in the tube1 an uniform temperature will be obtained2 if the ether continues to be agitated by breathing briskly through the tube1 a rapid reduction of temperature will be the result4 ,at the moment the ether is cooled down to the dew-point temperature1 the external surface of that portion ,page #dja of the silver tube containing the ether will become covered with a coating of moisture1 and the degree shown by the thermometer at that instant will be the temperature of the dew-point4 ,the most simple form of the hygrometer was formerly a very favourite indicator of the state of the weather1 and usually consisted of the figure of a monk with his hood1 which is attached to a bit of catgut2 this covering of paper1 painted to represent the hood1 falls over the head on the approach of damp weather1 and inclines well back during the period that the air is dry or contains less moisture2 and simple as it is1 this hygrometer1 in conjunction with the reading of the barometer1 may assist ,paterfamilias in deciding the fate of a pet bonnet or velvet mantle1 which is or is not to be worn on a doubtful day4 7,fig4 #cgh47 ,illustration3 ,fig4 #cgh4 ,the monk hygroscope1 in which the hood1 ,a ,b1 covers the head to dotted line ,c in wet weather1 and takes various intermediate positions1 being quite back and on the shoulders in dry states of the air4 ,a thermometer1 ,d1 is usually attached4 ,a decision on the possible changes of the weather requires considerable experience1 and it has been said that one of the most celebrated marshals of ,france owed his invariable success in military combinations and attacks to his attention to the signs of the weather1 as indicated by the state of the air during the phases of the moon4 ,inexperienced persons 7and by that we mean young persons7 may1 however1 take a certain position in the rank of weather prophets by consulting the weathercock1 the barometer1 and the hygrometer1 before committing themselves to an opinion1 if asked to say what the weather will be4 ,the dry and wet bulb hygrometer 7as represented in the next engraving7 consists of two parallel thermometers1 as nearly identical as possible1 mounted on a wooden bracket1 one marked dry1 the other wet4 ,the bulb of the wet thermometer is covered with thin muslin1 round the ,page #djb neck of which is twisted a conducting thread of lamp-wick1 or common darning-cotton2 this passes into a vessel of water1 placed at such a distance as to allow a length of conducting thread of about three inches2 the cup or glass is placed on one side1 and a little beneath1 so that the water within may not affect the reading of the dry bulb thermometer4 ,in observing1 the eye should be placed on a level with the top of the mercury in the tube1 and the observer should refrain from breathing whilst taking an observation4 ,the temperature of the air and of evaporation is given by the readings of the two thermometers1 from which can be calculated the dew-point1 tables being furnished for that purpose with the instrument4 7,fig4 #cgi47 ,illustration3 ,fig4 #cgi4 ,the dry and wet bulb hygrometer4 ,the colour of the sky at particular times affords the most excellent guidance to doubting members of pic-nic or other out-of-door parties4 ,not only does a rosy sunset presage fine weather1 and a ruddy sunrise bad weather1 but there are other tints which speak with equal clearness and accuracy4 ,a bright yellow sky in the evening indicates wind2 a pale yellow1 wet2 a neutral grey colour constitutes a favourable sign in the evening1 an unfavourable one in the morning4 ,the clouds1 again1 are full of meaning in themselves4 ,if their forms are soft1 undefined1 and feathery1 the weather will be fine2 if their edges are hard1 sharp1 and defined1 it will be foul4 ,generally speaking1 any deep1 unusual hues betoken wind or rain1 while the more quiet and delicate tints bespeak fine weather4 ,the principle of radiation of heat is employed by the ,indian natives in the neighbourhood of ,calcutta for the purpose of obtaining small ,page #djc quantities of ice4 ,in that climate1 the thermometer during the coldest nights does not indicate a lower temperature than about #dj ,fahr4 ,the sky1 however1 is perfectly cloudless1 and as heat radiates with great rapidity from the surface of the ground1 the ,indian natives ingeniously place very shallow earthenware pans on straw1 which is a bad conductor of heat1 and hence insulates the pans from communication with the parched earth4 ,in a few hours1 the water in the pans is covered with a thin sheet of ice1 and there can be no doubt of its production by an absolute loss of heat by radiation1 because the plan does not succeed on a windy night1 and succeeds best even when the pans are sunk in trenches dug in the earth4 ,a windy night prevents that difference of temperature between one portion of the surface of the earth and another1 which is so essential to a steady and uniform loss of heat1 as it must be evident that the continual mixture of warmer portions of air with that which is colder would tend to prevent the desired lowness of temperature being attained4 ,the manner in which heat is observed to be radiated has suggested another theory to the fertile brain of philosophical observers1 and it has been supposed that the conduction of heat may be nothing more than a radiation from one particle of matter to another1 as through a bar of copper1 in which the particles1 though packed closely together1 are not supposed to be in actual contact1 so that it is possible to conceive each separate atom of copper receiving and radiating its heat to the neighbouring particle1 and so on throughout the length and breadth of the metal4 ,by this theory the radiation of heat through a vacuum is brought into close connexion with that of the radiation of heat through the air and other solid and liquid bodies4 ,some of the most interesting phenomena of heat are those discovered by ,leslie1 who has proved in a very satisfactory manner that the rapidity with which a body cools1 depends 7like the reflection of light7 more on the condition of the surface than on the nature of the material of which the surface is composed4 ,with a globular and bright tin vessel it was observed that water of a certain heat contained in it1 required #aef minutes to cool2 but when the latter vessel was covered with a thin coating of lamp-black and size1 the water fell to the same degree as that noticed in the first experiment in the space of eighty-one minutes4 ,by very careful observations made with a differential air thermometer1 ,leslie determined that the power of radiating heat in various substances was as follows3-- ,lamp-black #ajj ,writing paper #ih ,sealing wax #ie ,crown glass #ij ,plumbago #ge ,tarnished lead #de ,clean lead #ai ,iron1 polished #ae ,tin plate #ab ,gold #ab ,silver #ab ,copper #ab ,page #djd ,as in the reflection of light1 it was noticed that a piece of charcoal covered with gold leaf1 partook of the nature of the precious metal so far as its power of throwing off or scattering the rays of light was concerned1 so a piece of glass covered with gold-leaf appears to possess the same power of radiating heat as that of any brilliant metal4 ,radiant heat1 like light1 can be propagated through a great variety of substances1 but is stopped by the larger number2 and it can be reflected1 refracted1 polarized1 absorbed1 or it may undergo a secondary radiation4 ,the intensity of radiant heat follows the same law as that of light1 and decreases as the square of the distance from its source4 ,the same law that governs the reflection of light1 also prevails with that of heat2 and it may be found by experiment that the angle of incidence is equal to the angle of reflection1 so that the heat is disposed of in the same manner as light when it falls upon bright polished planes1 convex and concave surfaces2 hence the use of bright tin meat screens and ,dutch ovens1 and of all those simple pieces of culinary furniture which are employed in the kitchen for the purpose of arresting the cold currents of air that set towards burning matter1 as also to reflect the heat upon whatever viands may be cooking before the fire4 ,a bright silver teapot retains its heat better than a dirty one1 and the fact is determined very readily by pouring boiling water into two teapots1 the one being made of bright tin and the other of black japanned tin4 ,a thermometer inserted into each vessel will soon show that the latter radiates1 and therefore loses its heat quicker than the former2 the relative radiating powers of bright and blackened tin being as #ae to #ajj4 ,pipes for the conveyance of hot water or steam should be kept bright1 if possible1 although this trouble is avoided usually by packing them in bad conductors of heat1 whilst the polish of the cylinder of a steam-engine is of great importance as a means of economizing heat4 ,illustration3 ,fig4 #chj4 ,a ,b4 ,the cone of paper1 gilt inside4 ,c4 ,the red-hot ball4 ,d4 ,stand with wood supporting a slice of phosphorus1 which is brought into the focus of the rays of heat reflected through the cone4 ,when the finger is approached within an inch or so of a red-hot ball1 the heat radiated from the latter is so intense that it cannot be held there ,page #dje for more than a few seconds4 ,if1 however1 the finger is coated with gold leaf it may be kept near the iron ball for some considerable time1 because the radiant heat is reflected from the surface of the gold4 ,if the word heat is written upon a sheet of paper and the letters afterwards gilt1 the whole of the white surface is rapidly toasted and scorched when held before a fire1 whilst the surface of the paper under the gold leaf remains perfectly white1 which can be ascertained by turning the paper round and observing the other side4 ,a sheet of paper gilt inside and turned round as a cone1 being left open at both ends1 may be employed as a reflecting surface2 and if a bit of phosphorus1 placed on paper1 is held1 say at two feet from a red-hot ball of about two inches diameter1 the radial heat from the latter has not sufficient intensity at that distance to set it on fire quickly2 if1 however1 the cone of gilt paper is used between the two1 and the phosphorus brought into the focus of the rays of radial heat1 it very quickly takes fire4 7,fig4 #chj47 ,dr4 ,bache has determined by experiments that the radiation of heat from a body is not affected by colour1 so that in winter all coloured clothes are alike in that respect1 and radiate heat without any appreciable difference4 ,the power of absorbing heat1 however1 is greatly dependent on colour2 and as a general rule1 good radiators of heat 7such as a black cloth1 or indeed any surface covered with lamp-black71 are also excellent absorbents of heat4 ,dr4 ,hooke and ,dr4 ,franklin placed pieces of cloth of similar texture and size on snow1 allowing the sun's rays to fall equally upon them4 ,the dark specimen always absorbed more heat than the light ones1 and the snow beneath them melted to a greater extent than under the others2 and they both remarked that the effect was nearly in proportion to the depth of the shade1 as in the following order3--,after black1 the maximum absorbent quality was possessed by1 first1 blue2 second1 green2 third1 purple2 fourth1 red2 fifth1 yellow4 ,the minimum absorbent power was observed to belong to white4 ,when radiant heat is allowed to pass through glass1 the latter substance is not found to be transparent to heat rays as it is to those of light1 but a considerable proportion of heat is arrested and stopped2 consequently glass fire-screens are to be found in the mansions of the wealthy1 because they obstruct the heat but do not exclude the cheerful light and blaze of the fireside4 ,melloni's researches on the nature of the rays of heat1 and also on the media which affect them1 would demand and merit a chapter to themselves2 want of space1 however1 obliges us to omit the consideration of thermo-electricity1 and the refined and beautiful experiments of ,melloni1 whose labours are a model for the imitation of all original seekers after truth4 ,page #djf ,,chapter ,,xxviii4 ,,the ,,steam-,,engine4 ,illustration3 ,fig4 #cha4 ,hancock's steam omnibus1 which ran on the common roads4 ,it must be apparent to those who read popular works on science1 that they possess1 at all events1 one point of utility--viz41 that they are indicative of the various subjects that may be selected in science for special1 searching and exhaustive study4 ,the subject of steam and the steam engine is not one that could be thoroughly treated of in the narrow space allowed in this volume1 but enough may be said to give some instruction and to impart common principles1 whilst the minute details are better examined and learnt in the works of ,bourne1 ,rankine1 and other authors who devote themselves specially to the important commercial question of steam4 ,the first truth to be comprehended is1 that all matter contains within its substance the power of creating heat--or as it may be expressed more plainly1 solids1 fluids1 and gases contain what is termed latent or insensible heat1 in contradistinction to the heat which is apparent when we touch a vessel containing warm water or approach a cheerful fire2 this latter is termed sensible heat1 and has formed the subject of the preceding chapters4 ,if a cold horse-shoe nail is applied to a thin dry slice of phosphorus laid on a sheet of paper1 no combustion of the phosphorus ensues1 because the temperature of the iron is not sufficiently high to affect that combustible substance2 but if the horse-shoe nail is vigorously hammered on an anvil1 the particles of the metal are brought closer together1 and if it is applied to the phosphorus1 so much heat has been generated1 thrust or squeezed out by the hammering or condensation of the iron1 that it is now sufficiently warm to set fire to it4 ,page #djg ,the reverse or antithesis to this experiment--viz41 the production of cold--would be shown if it were possible to expand a mass of metal suddenly1 and this can be effected by first melting together #bjg parts by weight of lead4 #aah tin4 #bhd bismuth4 ,when these metals are in the liquid state and perfectly mixed1 they are poured from a sufficient height into a pail of cold water1 for the purpose of granulating or dividing them into small fragments4 ,if the granulated compound metal is now mixed with #afag parts by weight of quicksilver1 it becomes suddenly liquefied and expanded3 liquefaction is the reverse of solidification1 and hence cold is produced from the natural heat of the compound metals being rendered latent by the change from the solid to the liquid state2 so that a small quantity of water placed in a glass tube1 and surrounded with the metals whilst liquefying in the mercury1 becomes rapidly converted into ice1 the fall of the temperature1 as shown by a thermometer1 being from #fj ,fahr4 to #ad1 which is #ah degrees below the freezing point of water4 ,in the former case1 by hammering the iron the latent heat is made sensible2 whilst in the latter case1 by the liquefaction of the compound metal in mercury1 the sensible heat is rendered latent4 ,the heat rendered latent by melting different substances is not a constant quantity1 but varies with every special body employed1 and the ,drs4 ,irvine have proved this fact by the following experiments3-- ,ditto1 reduced ,heat to the of specific heat fluidity4 of water4 ,sulphur #adc4fh ,fahr4 #bg4ad ,spermaceti #ade -- ,lead #afc #e4f4 ,bees'-wax #age -- ,zinc #dic #dh4c4 ,tin #ejj #cc4 ,bismuth #eej #bc4be4 ,every one of these substances requires more heat to bring them into the liquid condition than ice1 for which #adj of heat are sufficient1 or are rendered latent during its conversion into water4 ,in coining at the ,mint1 the cold blank pieces of gold1 silver1 or copper become hot directly they have sustained the violent and sudden pressure of the coining press1 and they must be heated again1 or annealed1 to restore the equilibrium of the heat disturbed by the violent blow1 or else they remain hard and unfit to sustain the finishing process of milling4 ,the condensation of water when it assumes a smaller bulk by union with sulphuric acid1 is easily proved by measuring a pint of water and a pint of acid1 and mixing them together1 when a very great increase of temperature may be perceived2 and by placing into the mixture a cold copper wire that previously could not ignite phosphorus1 it becomes ,page #djh very hot1 and when removed and wiped it will cause phosphorus to fire directly it touches that substance4 ,when the mixture of sulphuric acid and water is measured after it has cooled1 it has no longer a bulk of two pints1 but is found to have lost bulk equal to one or more ounces by measure4 ,the heat evolved by a mixture of four parts of strong sulphuric acid and one part water is shown by the thermometer to be #cjj ,fahr41 and this mode of obtaining heat has been used by aeronauts for the purpose of obtaining artificial warmth without the danger of setting fire to the gas in the balloon4 ,illustration3 ,fig4 #chb4 ,aeronauts in the car warming their hands by a bottle containing sulphuric acid and water4 ,when alcohol and water are mixed a change of density occurs1 and heat is produced2 and if equal measures of alcohol of a specific gravity of 4#hbe1 and water1 each at #ej ,fahr41 are mixed1 a temperature of #gj ,fahr4 is obtained2 if the mixture is made in a glass vessel1 as shown in the annexed cut1 the combination is very apparent4 ,to perform the experiment properly1 water is poured into the lower tube and bulb1 and alcohol into the top one2 when this is done1 the stopper is inserted1 and the whole thoroughly shaken and mixed together2 the warmth which is ,page #dji thus obtained is apparent to the hand1 whilst the contraction is shown after the mixture is cold1 as it no longer fills the two bulbs of the instrument4 7,fig4 #chc47 ,illustration3 ,fig4 #chc4 ,glass bulbs and tube to show the contraction in bulk of a mixture of alcohol and water4 ,the latent heat of gases is easily shown by suddenly condensing air in a small syringe or pump1 of which the piston contains a minute fragment of amadou 7a species of fungus1 ,polyporus igniarius2 this1 according to ,simmonds1 after having been beaten with a mallet1 and dipped in a solution of saltpetre1 forms the spunk or ,german tinder of commerce2 it is also used as a styptic1 and made into razor strops71 which takes fire1 and before the invention of vesta and other matches1 tobacco-smokers were in the habit of obtaining a light for their pipes and cigars in this manner--viz41 by the latent heat obtained from the contraction or compression of air4 ,then1 again1 an instructive though opposite parallel is afforded by suddenly expanding or rarefying air in a glass receiver provided with a delicate thermometer4 ,by pumping out some of the air1 a considerable diminution of the temperature occurs1 and equal to several degrees of the thermometer4 ,every child knows that steam direct from the kettle will scald1 but if it issues from a high-pressure boiler1 say at fifteen pounds on the square inch1 the hand may be held with impunity in the escaping steam1 as it merely feels gently warm1 and not scalding4 ,this is due partly to the loss of heat rendered latent by the expansion of the high-pressure steam directly it passes into the air1 and partly to the currents of air that are dragged into an escaping jet of steam4 ,this tendency of the air to rush into a jet of steam was discovered by ,faraday1 and explains those curious experiments with a jet of steam by which balls1 empty flasks1 and globular vessels are sustained and supported either perpendicularly or horizontally4 ,illustration3 ,fig4 #chd4 ,a4 ,jet discharging high-pressure steam ,b ,b4 ,lighted torch held round the escaping steam the flames from the former all rush into the latter4 ,if steam at a pressure of about sixty pounds per inch is allowed to escape from a proper jet1 and a large lighted circular torch composed of tow dipped in turpentine held over it1 the course of the external air is shown1 by the direction of ,page #daj the flames1 which are forcibly pulled and blown into the jet of steam with a roaring noise1 indicating the rapidity of the blast of air moving to the steam jet4 7,fig4 #chd47 ,egg-shells1 empty flasks1 india-rubber or light copper and brass balls1 are suspended in the most singular manner inside an escaping jet of high-pressure steam2 and before the explanation of ,faraday1 reams of paper were used in the discussion of the possible theory to account for this effect2 and what made the explanation still more difficult1 was the fact that the jet of steam might be inclined at any angle between the horizontal and perpendicular1 and still held the ball1 egg-shell1 or other spherical figure firmly in its vapory grasp4 7,fig4 #che47 ,illustration3 ,fig4 #che4 ,a4 ,ball and socket jet at an angle1 and discharging steam4 ,the egg-shells are supported by the enormous current of air moving into the jet in the direction of the arrows4 ,in consequence of the great rush of air towards a jet of escaping high-pressure steam1 ,mr4 ,goldsmith ,gurney has patented the application of this principle in his ventilating steam jet1 which he has already successfully applied2 in one case especially1 where a coal-mine had been on fire for several years1 and the whole working of the coal-measures in the pit was jeopardized by the spreading of the combustion to new workings2 the fire was first extinguished by carbonic acid gas1 pulled1 as it were1 into the coal-mine by a jet of steam blowing into the downcast1 but placed in connexion with a furnace of burning coke2 and the circulation of the carbonic acid1 called choke-damp1 through the pit workings was further assisted by a jet of high-pressure steam blowing upwards1 and placed over the mouth of the upcast shaft4 ,the experiment succeeded perfectly at the ,south ,sauchie ,colliery1 near ,alloa1 about seven miles from ,stirling1 where a fire had raged for about thirty years over an area of twenty-six acres in the waste seam of coal nine feet thick4 7,fig4 #chf47 ,for the general purpose of ventilating the coalmine1 ,mr4 ,gurney's plan was tried at the ,ebbw ,vale ,colliery1 and very economically1 the waste steam alone being used4 ,experiments have also been satisfactorily made with it for blowing a cupola for smelting iron1 and with dry steam--i4e41 steam of a very high pressure--escaping through a warm tube1 the results were perfectly successful4 ,page #daa ,illustration3 ,fig4 #chf4 ,gurney's steam jet4 ,a4 ,furnace4 ,b4 ,water tank4 ,c4 ,downcast stopping4 ,d4 ,upcast stopping4 ,e ,e ,e4 ,steam jets4 ,f ,f4 ,galleries from shaft to shaft4 ,page #dab ,with this digression from the subject of latent heat derived from the compression of air1 we return again to the subject with another case in point1 furnished by the ,fountain of ,hiero1 as it is called1 at ,schemnitz1 in ,hungary1 described by ,professor ,brande2 and it may be observed that all the phenomena related would apply to the great pressure of the water from the water-towers at the ,crystal ,palace1 if fitted with a similar air-vessel4 ,a part of the machinery for working these mines is a perpendicular column of water #bfj feet high 7the ,crystal ,palace water-towers are each #bhd feet high71 which presses upon a quantity of air enclosed in a tight reservoir2 the air is consequently condensed to an enormous degree by this height of water1 which is equal to between eight and nine atmospheres2 and when a pipe communicating with this reservoir of condensed air is suddenly opened1 it rushes out with extreme velocity1 instantly expands1 and in so doing it absorbs so much heat as to precipitate the moisture it contains in a shower of snow1 which may readily be gathered on a hat held in the blast4 ,the force of this is so great1 that the workman who holds the hat is obliged to lean his back against the wall to retain it in its position4 ,the best examples of latent heat are furnished by ice1 water1 and steam1 and we are indebted chiefly to ,dr4 ,black for the elegant and conclusive experiments demonstrating the important truths connected with the latent heat of these three conditions of matter4 ,when various solids are heated1 they frequently pass through certain intermediate conditions of softness1 terminating in perfect liquidity2 but ice and many other bodies change at once to the liquid state on the application of a sufficient quantity of heat4 ,the process of melting ice is very slow1 because every portion must absorb or render latent a certain quantity of heat before it can take the liquid state--hence the difficulty of melting blocks of ice when they are surrounded with non-conducting materials2 and this fact the author has proposed to take advantage of in keeping water cool which is to be supplied to the ova of salmon whilst taking them to stock the rivers of ,australia4 ,in order to prove that heat is rendered latent by the liquefaction of ice1 it is only necessary to weigh a pound of finely-powdered ice and a pound of water at #bab ,fahr4 7boiling water71 and mix them together2 when the ice is all melted1 the resulting temperature is only #eb1 therefore the boiling water has lost #afj of temperature1 of which #bj can be accounted for1 because the resulting temperature of the melted ice is #eb2 but in the liquefaction of the pound of ice1 #adj have disappeared or become latent1 or1 as ,dr4 ,black termed it1 have become combined4 #a lb4 of ice at #cb #bj #eb1 the resulting temperature4 #a lb4 of water at #bab - #eb #afj - #bj #adj1 rendered latent4 #adj represents the result obtained from innumerable experiments made by mixing equal parts of ice and boiling water1 and it is this large quantity of latent heat required by ice and snow that prevents their sudden liquefaction1 and the disastrous circumstances that would arise from the floods that must otherwise always be produced4 ,page #dac ,to put the fact beyond all doubt1 it is advisable to mix together equal weights of water at #cb and boiling water at #bab1 and the result is found by the thermometer to be the mean between the two1 because half the extremes are always equal to the mean2 and if the two temperatures are added together and divided by two1 the result is a temperature of #abb1 as shown below3-- #a lb4 of ice water at #cb #a lb4 of water at #bab #bdd #b #abb4 ,from similar experiments ,dr4 ,black deduced the important truth1 that in all cases of liquefaction a quantity of heat not indicated by1 or sensible to1 the thermometer1 is absorbed or disappears1 and that this heat is withdrawn from the surrounding bodies1 leaving them comparatively cold4 ,at p4 #gi it is shown how the sudden solution or liquefaction of certain salts produces cold1 and hence numerous freezing mixtures have been devised4 ,in olden times1 when officials in authority did what they pleased1 without being troubled with disagreeable returns1 and colonels clothed their men1 and were merchant tailors on the grand scale1 gun cartridges were not confined to practice on the enemy1 but they did duty frequently in the absence of ice as refrigerators of the officers' wine1 in consequence of the gunpowder containing nitre or saltpetre2 as a mere solution of this salt finely powdered will lower the temperature of water from #ej ,fah4 to #ce2 whilst a mixture of four ounces of carbonate of soda and four ounces of nitrate of ammonia dissolved in four ounces of water at #fj1 will in three hours freeze ten ounces of water in a metallic vessel immersed in the mixture during the liquefaction or solution of the salts4 ,fahrenheit imagined he had attained the lowest possible temperature by mixing ice and salt together1 and it is by this means that confectioners usually freeze their ices1 or ice puddings2 the materials are first incorporated1 and being placed in metallic vessels or moulds1 and surrounded with ice and salt placed in alternate layers1 and then well stirred with a stick1 they soon solidify into the forms which are so agreeable1 and so frequently presented at the tables of the opulent4 ,the temperature obtained is ,fahrenheit's zero--viz41 thirty-two degrees below the freezing point of water4 ,according to the very wise police regulation observed in ,london1 all householders are required to sweep or remove the snow from the pavement in front of their houses1 and this is frequently done with salt2 should an unfortunate shoeless beggar1 tramp past whilst the sudden liquefaction is in progress1 the effect on the soles of his feet is evidently very disagreeable1 and the rapidity with which he retires from the zero affords a thermometric illustration of the most lively description4 ,heat the ,cause of ,vapour4 ,every liquid1 when of the same degree of chemical purity1 and under equal circumstances of atmospheric pressure1 has one peculiar point of temperature at which it invariably boils4 ,thus1 ether boils at #if ,fahr41 and if some of this highly inflammable liquid is placed carefully in a ,page #dad flask1 by pouring it in with a funnel1 and flame applied within one inch of the orifice1 no vapour escapes that will take fire2 but if the flame of a spirit lamp is applied1 the ether soon boils1 and if the lighted taper is again brought near the mouth of the flask1 the vapour takes fire1 and produces a flame of about two feet in length4 ,this fire only continues as long as the flame of the spirit-lamp is retained at the bottom of the flask1 and on removing it the vessel rapidly cools4 ,the length of the flame is reduced1 and is gradually extinguished for the want of that essence of its vitality1 as it were--viz41 heat4 7,fig4 #chg47 ,if a thermometer is introduced into the flask1 however rapid may be the ebullition or boiling of the ether1 it is found to be invariably at #if4 ,the heat carried off by evaporation is most elegantly displayed by placing a little water in a watch glass1 and surrounded by charcoal saturated with sulphuric acid1 in the vacuum of an air-pump4 ,the rapid evaporation and condensation of the water by its affinity for the sulphuric quickly produces ice2 and the pumps and other apparatus of ,knight and ,co41 ,foster-lane1 ,city1 are greatly to be recommended for this and other illustrations4 ,illustration3 ,fig4 #chg4 ,heat the cause of vapour4 ,the illustration of the determination of the fixed and invariable boiling point belonging to every liquid is further carried out by introducing some water into a second flask standing above a lighted spirit-lamp1 with a small thermometer1 graduated1 of course1 properly to degrees above the boiling point of water2 when the water boils1 it will be found to remain steadily at a temperature of #bab4 ,and however rapidly the water may be boiled1 provided there is ample room for the steam to escape1 the heat indicated by the thermometer is like the law of the ,medes and ,persians1 which altereth not1 and it remains standing at the number #bab4 ,the only exception 7if it may be so termed7 to this law is brought about by the shape and nature of the containing vessel2 under a mean pressure the boiling point of water in a metallic vessel is generally #bab2 in a glass vessel it may rise as high as #bad or #baf1 but if some metallic filings are dropped in1 the escape of steam is increased1 and the temperature may then drop immediately to #bab4 ,when a thermometer is inserted in a flask containing water in a state ,page #dae of ebullition or boiling1 so that the bulb does not touch the fluid1 but is wholly surrounded with steam1 it will be found that the temperature of the latter is exactly the same as that of the former2 and if the liquid boils at #if1 the vapour will be #if1 if at #bab1 the steam is #bab4 ,steam has therefore exactly the same temperature as the boiling water that produces it4 7,fig4 #chh47 ,illustration3 ,fig4 #chh4 ,thermometer in the steam escaping from boiling water4 ,whilst performing the last experiment1 it may be noticed that the steam inside the neck of the flask is invisible1 and that it only becomes apparent in that kind of intermediate condition between the vaporous and liquid state called vesicular vapour--a state corresponding with the earth fog1 and called by ,howard the stratus4 ,when a flask containing boiling water is placed under the receiver of an air pump 7as soon after the ebullition has ceased as may be possible71 and the air pumped out1 it will be noticed that the water again begins boiling as the vacuum is obtained1 showing that the boiling point of the same fluid varies under different degrees of atmospheric pressure1 and according to the height of the barometer4 ,height of ,boiling point barometer4 of water4 #bf #bjd4ia #bf4e #bje4gi #bg #bjf4fg #bg4e #bjg4ee #bh #bjh4dc #bh4e #bji4ca #bi #baj4ai #bi4e #baa4jg #cj #bab #cj4e #bab4hh #ca #bac4gf ,alcohol and ether confined under an exhausted receiver boil violently at the ordinary temperature of the atmosphere1 and in general liquids boil with #abd less of heat than are required under a mean pressure of the air2 water1 therefore1 in a vacuum must boil at #hh and alcohol at #di4 ,on ascending considerable heights1 as to the tops of mountains1 the boiling point of water gradually falls in the scale of the thermometer4 ,thus1 on the summit of ,mont ,blanc water was found by ,saussure to boil at #ahg ,fahr4 ,in ,mr4 ,albert ,smith's delightful narrative of his ascent of ,mont ,blanc1 he mentions the violent commotion and escape of the whole of the champagne in froth directly the bottle was opened at the summit of this king of mountains4 ,dr4 ,wollaston's instrument for measuring the heights of mountains by ,page #daf the variations of the boiling point of water has long been known and used for this purpose4 ,if a ,florence flask is first fitted with a nice soft cork1 and this latter removed1 and the former half filled with water1 which is then boiled over a gas or spirit flame1 the same fact already mentioned and illustrated in the preceding table may be rendered apparent when the flask is corked and removed from the heat4 ,if it is now inverted1 and cold water poured over it1 an ebullition immediately commences1 because the cold water condenses the steam in the space above the hot water in the flask1 and producing a vacuum1 the water boils as readily as it would do under an exhausted receiver on an air-pump plate4 7,fig4 #chi47 ,illustration3 ,fig4 #chi4 ,the paradoxical experiment of water boiling by the application of cold water4 ,water may be heated considerably higher than #bab1 if it is enclosed in a strong boiler1 and shut off from communication with the air2 by this means steam of great pressure is obtained4 ,dr4 ,marcet has invented a very instructive form of a miniature boiler1 supplied with a thermometer and barometric pressure gauge1 which can be purchased at any of the instrument makers1 and is figured and described in nearly every work on chemistry4 ,the reason water boiled in an open vessel does not rise to a higher temperature than #bab is because all the excess of heat is carried off by the steam1 and is said to be rendered latent in the vapour4 ,the fixation of caloric in water by its conversion into steam may be shown by the following experiment4 ,let a pound of water at #bab and eight pounds of iron filings at #cjj be suddenly mixed together4 ,a large quantity of steam is instantly generated1 but the temperature of the water and escaping steam are still only #bab2 hence the steam must therefore contain all the degrees of heat between #bab and #cjj1 or eight times #hh4 ,when the water is heated in the hydro-electric machine or other boiler1 to #cbb4g1 it very quickly drops to #bab when the steam is allowed to blow off2 yet if the latter is collected1 it represents but a very small quantity of water which constituted the steam1 and it has carried off and rendered latent the excess of heat in the boiler--viz41 the difference between #bab and #cbb4g1 or #aaj4g ,if steam can carry off heat1 of course it may be compelled1 as it were1 ,page #dag to surrender it again2 and this important elementary truth is shown by adapting a tube1 bent at right angles1 and a cork1 to a flask containing a few ounces of water1 and when it boils1 the steam issuing from the end of the pipe may now be directed into and below the surface of some water contained in a beaker glass2 in a very short time the water in the latter will be raised to the boiling point by the condensation of the steam and the latent heat arising from it4 7,fig4 #cij47 ,the amount of latent heat is enormous1 when it is remembered that water by conversion into steam has its bulk prodigiously enlarged--viz41 #afih times1 so that a cubic inch of water converted into steam of a temperature of #bab1 with the barometer at thirty inches1 occupies a space of one cubic foot1 and its latent heat amounts1 according to ,hall1 to #iej2 ,southeron1 #ide2 ,dr4 ,ure1 #ifg4 ,when we come to the consideration of the steam-engine1 it will be noticed that the question of the latent heat of steam is one of the greatest importance4 ,illustration3 ,fig4 #cij4 ,a4 ,flask for generating steam4 ,b4 ,glass pipe bent at right angles to convey the steam into the fluid containing some cold water4 ,temperature of ,elasticity in inches ,latent ,heat4 ,steam4 of ,mercury4 #bbi #dj #idb #bgj #hj #idb #bie #abj #iej ,the same weight of steam contains1 whatever may be its density1 the same quantity of caloric1 its latent heat being increased in proportion as its sensible heat is diminished2 and the reverse4 ,in consequence of the enormous amount of latent heat contained in steam1 it is advantageously employed for the purpose of imparting warmth either for heating rooms or drying goods in certain manufacturing processes4 ,the wet rag-pulp pressed and shaken into form on a wire-gauze frame or deckle1 passes gradually to cylinders containing steam1 and is thoroughly dried before the guillotine knife descends at the end of the paper machine1 and cuts it into lengths4 ,in calico stiffening and glazing1 also in calico printing1 steam-heated cylinders are of great value1 because they impart heat without the chance of setting the goods on fire4 ,the elementary principles already described with reference to heat1 will prepare the youthful reader for the application of the expansion of water into steam1 as the most valuable motive power ever employed to assist the labour of man4 ,page #dah ,,chapter ,,xxix4 ,,the ,,steam-,,engine--continued4 ,illustration3 ,fig4 #cia4 ,the first steam-boat1 the ,comet1 built by ,henry ,bell1 in #ahaa1 who brought steam navigation into practice in ,europe4 ,so shalt thou instant reach the realm assign'd ,in wondrous ships1 self-mov'd1 instinct with mind4 99 99 99 99 99 ,though clouds and darkness veil the encumbered sky4 ,fearless1 through darkness and through clouds they fly1 ,tho' tempests rage1--tho' rolls the swelling main1 ,the seas may roll1 the tempests swell in vain2 ,e'en the stern god that o'er the waves presides1 ,safe as they pass1 and safe repass the tides1 ,with fury burns2 while careless they convey1 ,promiscuous1 ev'ry guest to ev'ry bay4 ,these lines1 from ,pope's translation of the ,odyssey1 were very aptly quoted twenty-five years ago by ,mr4 ,m4 ,a4 ,alderson1 in his treatise on the steam-engine1 for which he received from ,dr4 ,birkbeck1 the ,page #dai originator of ,mechanics' ,institutions1 the prize of #bjl41 being the gift of the ,london ,mechanics' ,institution1 and these lines seem to indicate some sort of rude anticipation by the ancients of that free passage of the ocean by the agency of steam which has rendered ships almost independent of wind and weather4 ,homer's description1 as above1 of the ,phoenician fleet of ,king ,alcinous1 in the eighth book of the ,odyssey1 is certainly an ancient record of an idea1 but nothing more4 ,in a work written by ,hero of ,alexandria1 about a hundred years ,b4,c41 and entitled ,spiritalia seu ,pneumatica1 a number of contrivances are mentioned for raising liquids and producing motion by means of air and steam1 so that the first steam-engine is usually ascribed to ,hero2 and the annexed cut displays the apparatus4 7,fig4 #cib47 ,illustration3 ,fig4 #cib4 ,hero's steam-engine4 ,a4 ,the boiler in which steam is produced1 and then passes through the hollow support ,b1 from which there is no outlet but through the two apertures1 ,c ,c4 ,the reaction of the air on the issuing steam produces a rotatory motion in the jets1 ,c ,c1 attached to a centre but hollow axle4 ,it is a remarkable circumstance that ,sir ,isaac ,newton applied the same principle in a little ball1 mounted on wheels1 containing boiling water1 and provided with a small orifice2 and in his description he says3 ,and if the ball be opened1 the vapours will rush out violently one way1 and the wheels and the ball at the same time will be carried the contrary way4 ,from the time of ,hero1 there does not appear to be any record or mention made of steam apparatus till the year #ajjb1 when1 in a work called ,malmesbury's ,history1 mention is made of an organ in which the sounds were produced by the escape of air 7query1 steam7 by means of heated water4 ,it is strange that1 in these days of steam application1 the ,calliope1 or steam organ1 should be an important feature at the present moment at the ,crystal ,palace2 and it only shows how the same ideas are reproduced as novelties in the ever-recurring cycles of years4 ,on the revival of classical learning throughout ,gothic ,europe1 the work of ,hero began to attract attention1 and it was translated and printed in black letter1 and most likely first from the ,arabic character1 as in the year #aedc the first fruits appeared in ,spain1 where ,blasco de ,garay1 a sea captain1 propelled a ship of #bjj tons burden1 at the rate of three miles per hour1 before certain commissioners appointed by the ,emperor ,charles the ,fifth4 ,alas for inquisitorial ,spain6 had she looked deeper into the matter1 and performed her auto-da-fes on the boilers of ,page #dbj steam engines instead of the bodies of poor human beings1 what lasting glories would have been her reward4 ,the invention made its dbut in ,spain1 the commissioners reported1 the worthy inventor was rewarded1 but the mighty giant invoked was put to sleep again for at least #aej years4 ,the steam giant was disturbed with dreams2 one ,mathias1 in #aefc1 gave him a nightmare2 ,solomon de ,caus1 in #afbd1 nearly woke him up2 ,giovanni ,bianca1 in #afbi1 did more2 and the ,marquis of ,worcester1 in the middle of the seventeenth century1 as the evil genius of ,spain1 carried off the giant bodily and made him the slave of ,england2 at least1 he experimented1 and wrote such wondrous tales of his new motive power1 that in #afec we read of steam being fairly tethered to its work1 and set to draw water out of the ,thames at ,vauxhall2 and ,cosmo de ,medici1 a foreigner who inspected the apparatus in #afec1 says1 ,it raises water more than forty geometrical feet by the power of one man only1 and in a very short space of time will draw up full vessels of water through a tube or channel not more than a span in width1 on which account it is considered to be of greater service to the public than the other machine near ,somerset ,house1 which last one was driven by two horses4 ,what would the ,marquis of ,worcester and ,cosmo de ,medici have thought of ,blasco de ,garay on the ocean1 and ruling #ab1jjj steam horses8 ,write the name of the brave and prudent ,captain ,harrison1 in the good ship ,great ,eastern1 date #ahei1 instead of that of the gallant ,spaniard1 and our brief history is finished4 ,the first really useful steam-engine was made1 not by a plain ,mr41 but again by a captain--namely1 ,captain ,savery1 who appears to have been the first inventor who thoroughly understood and applied the vacuum principle4 7,fig4 #cic47 ,page #dba ,illustration3 ,fig4 #cic4 ,savery's engine4 ,a ,a4 ,the furnaces which contain the boiler4 ,b #a and ,b #b4 ,the two fireplaces4 ,c4 ,the funnel or chimney1 which is common to both furnaces4 ,in these two furnaces are placed two vessels of copper1 which ,i 7,savery7 call boilers--the one large as at ,l1 the other small as ,d4 ,d4 ,the small boiler contained in the furnace1 which is heated by the fire at ,b #b4 ,e4 ,the pipe and cock to admit cold water into the small boiler to fill it4 ,f4 ,the screw that covers and confines the cock ,e to the top of the small boiler4 ,g4 ,a small gauge cock at the top of a pipe1 going within eight inches of the bottom of the small boiler4 ,h4 ,a large pipe which goes the same depth into the small boiler4 ,i4 ,a clack or valve at the top of the pipe ,h 7opening upwards74 ,k4 ,a pipe going from the box above the said clack or valve in the great boiler1 and passing about one inch into it4 ,l ,l4 ,the great boiler contained in the other furnace1 which is heated by fire at ,b #a4 ,m4 ,the screw with the regulator1 which is moved by the handle ,z1 and opens or shuts the apertures at which the steam passes out of the great boiler at the steam-pipes ,o ,o4 ,n4 ,a small gauge cock at the top of a pipe1 which goes half way down into the great boiler4 ,o #a1 ,o #b4 ,steam pipes1 one end of each screwed to the regulator2 the other ends to the receivers ,p ,p1 to convey the steam from the great boiler into those receivers4 ,p #a1 ,p #b4 ,copper vessels called receivers1 which are to receive the water which is to be raised4 ,q4 ,screw joints by which the branches of the water-pipes are connected with the lower parts of the receivers4 ,r #a1 #b1 #c1 and #d4 ,valves or clacks of brass in the water-pipes1 two above the branches ,q and two below them2 they allow the water to pass upwards through the pipes1 but prevent its descent2 there are screw-plugs to take out on occasions to get at the valves ,r4 ,s4 ,the forcing-pump which conveys the water upwards to its place of delivery1 when it is forced out from the receivers by the impelled steam4 ,t4 ,the sucking-pipe1 which conveys the water up from the bottom of the pit to fill the receivers by suction4 ,v4 ,a square frame of wood1 or a box1 with holes round its bottom in the water1 to enclose the lower end of the sucking-pipe to keep away dirt and obstructions4 ,x is a cistern with a bung cock coming from the force-pipe1 so as it shall always be kept filled with cold water4 ,y ,y4 ,a cock and pipe coming from the bottom of the said cistern1 with a spout to let the cold run down on the outside of either of the receivers1 ,p ,p4 ,z4 ,the handle of the regulator to move it by1 either open or shut1 so as to let the steam out of the great boiler into either of the receivers4 ,page #dbb ,this is ,savery's own description 7taken from the ,miner's ,friend1 printed in #agjb71 of his water-engine1 which differs from that suggested by the ,marquis of ,worcester1 in the fact that he made the pressure of the air carry the water up the first stage4 ,savery's patent was for raising water and occasioning motion to all sorts of mill-work by the impellant force of fire2 and the patent was granted in the reign of ,king ,william the ,third of glorious memory4 ,thus ,savery overcame1 as he remarks1 the oddest and almost insuperable difficulties1 and introduced a steam apparatus or engine1 a good many of which were constructed1 and employed for raising water4 ,the mechanical skill required to construct the boiler1 the very heart 7as it were7 of the iron engine1 had not been acquired in the time of ,captain ,savery1 and hence the weakness of the boilers1 and the danger of working them4 ,as the pressure required was very considerable to overcome the resistance of a lofty column of water1 these engines were gradually relinquished for those of another clever mechanician--viz41 for those of ,thomas ,newcomen1 an ironmonger of ,dartmouth1 who1 about the year #agje1 constructed and introduced the cylinder1 from which the transition was gradually made to the mode of condensing by a jet of cold water1 the use of self-acting valves1 and the construction of self-acting engines by ,smeaton1 ,hornblower1 and finally by the illustrious ,watt1 whose portrait heads the first chapter on ,heat in this book4 ,newcomen was assisted in his work by one ,cawley1 a glazier2 and their persevering labours were crowned with a successful result of the most memorable importance in the history of the steam-engine4 ,in the engine by ,savery1 the operation of the steam was twofold--namely1 by the direct pressure from its elasticity1 and by the indirect consequence of its condensation1 which affords a vacuum4 ,this last may be said to be the only principle used by ,newcomen1 who employed a boiler for the generation of steam1 and conveyed it by a pipe to the bottom of a hollow cylinder1 open at the top1 but provided with a solid piston1 that moved up and down in it1 and was rendered tight by a stuffing of hemp1 like the piston of a boy's common squirt4 ,it can readily be understood1 that if the jet of the latter was connected with a tight little boiler1 and steam blown into it1 that the piston of the squirt would rise to the top of the barrel in which it works1 being thrust up by the pressure or force of the steam2 but unless the steam was cut off1 and cold water applied to the interior of the barrel1 the piston could not descend again4 ,as soon1 therefore1 as ,newcomen had thrust up the piston by the action of steam1 he introduced a jet of cold water1 supplied from an elevated cistern beneath the piston1 when the steam was condensed into water1 and a vacuum or void space obtained4 ,the piston being free to move either up or down1 was now forced in the latter direction by the pressure of the air1 which is a constant force equal to fifteen pounds on the square inch2 and thus the piston in ,newcomen's engine was raised by heat--viz41 by steam1 and thrust down by cold--i4e41 by the condensation of the steam producing a vacuum4 ,the void obtained in this manner was very considerable1 because one cubic foot of ,page #dbc steam at #bab condenses into one cubic inch of water4 ,the production of a vacuum with the aid of steam is quickly effected by boiling some water in a clean camphine can1 and when the steam is issuing freely from the mouth of the latter it is then corked1 and cold water thrown over the exterior4 ,directly the temperature is lowered1 the steam inside the tin vessel is condensed suddenly into water1 and a void space being suddenly obtained1 the whole pressure of a column of air of a breadth equal to the area of the vessel1 and of a height of forty miles1 is brought suddenly down like a sledge-hammer upon the sides of the tin vessel1 and as they are not sufficiently strong to offer a proper resistance1 they are crushed in like an egg-shell by the giant weight which falls upon them4 ,the barometer1 or measurer of the weight of the air1 consists of a glass tube about thirty-three inches in length1 hermetically sealed at one end1 and containing mercury that has been carefully boiled within it1 and being perfectly filled the tube is inserted in a cistern of clean mercury1 when it gravitates to a height equal to the pressure of the air1 leaving a space at the top called the torricellian vacuum4 ,as the atmospheric air decreases in density by admixture with invisible steam or vapour1 any given volume becomes specifically lighter3 hence the column of mercury falls to a height of about twenty-eight inches2 whilst if the aqueous vapour diminishes1 the weight of the air becomes greater1 and the barometer may rise to a height of about thirty-one inches4 ,having thus secured a reciprocating motion1 ,newcomen applied it to the working of a force-pump by the intervention of a great beam or lever suspended on gudgeons 7an iron pin on which a wheel or shaft of a machine turns7 at the middle1 and suspended like the beam of a pair of scales2 and1 in fact1 he invented that method of supporting the beam which is in use to the present day4 ,supposing we compare ,newcomen's beam to a scale beam1 he attached to the extremities 7instead of scale pans7 a water pump and his steam cylinder--the latter being at one end1 and the former at the other4 ,the beam played at see-saw3 by the primary action of the steam on the bottom of the piston in the cylinder it was pushed up at this end1 and of course suffered an equal fall at the other1 to which the pump piston was attached2 and when the motion was reversed by the condensation of the steam1 down went the piston again by the pressure of the air1 whilst that of the water pump was again raised1 and being provided with proper valves1 the water was pumped slowly out of the mine1 although the steam power used was very moderate1 and only just sufficient to counterpoise the weight of the atmosphere4 ,newcomen made the end attached to the water pump purposely heavier than the steam piston of the other end of the beam1 and by this means the work of the steam1 by its elasticity1 was very moderate1 whilst the actual lift of the water from the mine was performed by the pressure of the air1 equal 7as already stated7 to fifteen pounds on every square inch of the surface of the steam piston4 ,this engine is called the atmospheric engine1 and in the next cut we have a picture taken from a photograph by the ,watt ,club of the actual model of the ,newcomen engine in the ,page #dbd ,hunterian ,museum of the ,university of ,glasgow2 the dimensions being--length1 #bg in42 breadth1 #ab in42 height1 #ej in42 from which1 in #agfe1 ,james ,watt1 in seeking to repair this model1 belonging to the ,natural ,philosophy ,class in the ,university of ,glasgow1 made the discovery of a separate condenser1 which has identified his name with that of the steam-engine4 7,fig4 #cid47 ,illustration3 ,fig4 #cid4 ,model of the ,newcomen engine1 in which the furnace and boiler1 the steam cylinder1 beam1 water-pump1 and elevated cistern of water1 are apparent4 ,in ,newcomen's engine1 the opening and shutting of the cocks required the vigilant care of a man or boy1 and it is stated on good authority that a boy who preferred 7like nearly all other boys7 play to work1 contrived1 by means of strings1 a brick1 and one or two catches on the working beam1 to make the engine self-acting4 ,this poor boy's ingenious contrivance paved the way for the improved ,page #dbe methods of opening and shutting the valves1 which were brought to a great state of perfection by ,beighton1 of ,newcastle1 about #agah4 ,between that time and the year #agfc1 we find honourable mention made of ,smeaton in connexion with the steam-engine1 but the name of the great ,james ,watt at this time began to be appreciated1 and by a series of wonderfully simple mechanisms1 he at last perfected the machine whose origin could be traced back not only to the time of ,blasco de ,garay1 in #aedc1 but even to the days of the ancient mechanicians1 such as ,hero1 who lived #acj ,b4,c4 ,in #agfc1 ,james ,watt was a maker of mathematical instruments in ,glasgow1 and his attention was drawn to the subject of the steam-engine by his undertaking to repair a working model of ,newcomen's steam-engine1 which was used by ,professor ,anderson1 who then filled the ,chair of ,natural ,philosophy1 and subsequently founded the ,andersonian ,institution4 ,the repairs required for this model induced ,watt to make another1 and by watching its operation1 he discovered that a vast quantity of heat1 and therefore fuel1 was wasted in the constant and successive heating and cooling of the steam cylinder4 ,about two years after1 when ,watt was twenty-nine years of age1 he had made so many experiments1 that he was enabled to put into a mechanical shape his original ideas1 which are embodied in his patent of #agfi1 as follows3-- ,my method of lessening the consumption of steam1 and consequently fuel1 in fire-engines1 consists of the following principles3 ,first3 ,that vessel in which the powers of steam are to be employed to work the engine1 which is called the cylinder in common fire-engines1 and which ,i call the steam-vessel1 must1 during the whole time the engine is at work1 be kept as hot as the steam that enters it--first1 by enclosing it in a case of wood or any other materials that transmit heat slowly2 secondly1 by surrounding it with steam or other heated bodies2 and thirdly1 by suffering neither water nor any other substance colder than steam to enter or touch it during that time4 ,secondly3 ,in engines that are to be worked wholly or partially by condensation of steam1 the steam is to be condensed in vessels distinct from the steam-vessels or cylinders1 although occasionally communicating with them2 these vessels ,i call condensers2 and whilst the engines are working1 these condensers ought at least to be kept as cold as the air in the neighbourhood of the engine1 by application of water or other cold bodies4 ,thirdly3 ,whatever air or other elastic vapour is not condensed by the cold of the condenser1 and may impede the working of the engine1 is to be drawn out of the steam-vessels or condensers by means of pumps wrought by the engines themselves1 or otherwise4 ,fourthly3 ,i intend in many cases to employ the expansive force of steam to press on the pistons1 or whatever may be used instead of them1 in the same manner as the pressure of the atmosphere is now employed in common fire-engines4 ,in cases where cold water cannot be had in plenty1 the engines may be wrought by this force of steam only1 by discharging the steam into the open air after it has done its office4 ,lastly3 ,instead of using water to render the piston or other parts of ,page #dbf the engines air and steam-tight1 ,i employ oils1 wax1 resinous bodies1 fat of animals1 quicksilver1 and other metals in their fluid state4 ,and the said ,james ,watt1 by a memorandum added to the said specification1 declared that he did not intend that anything in the fourth article should be understood to extend to any engine when the water to be raised enters the steam-vessel itself1 or any vessel having an open communication with it4 ,about the time he obtained his patent1 ,watt commenced the construction of his first real engine1 the cylinder of which was eighteen inches in diameter1 and after many impediments in the details of the work he succeeded in bringing it to considerable perfection4 ,the bad boring of the cylinder1 and the difficulty of obtaining a substance that would keep the piston tight without enormous friction1 and at the same time resist the action of steam1 gave him the most trouble1 and the employment of a piston rod moving through a stuffing-box was a new feature in steam-engines at that time1 and required great nicety of workmanship to make it effectual4 ,while ,watt was contending with these difficulties1 ,roebuck's finances became disarranged1 and in #aggc he disposed of his interest in the patent to ,mr4 ,boulton1 of ,soho4 ,as1 however1 a considerable part of the term of fourteen years1 for which the patent was granted1 had already passed away1 and as several years more would probably elapse before the improved engines could be brought into operation1 it was judged expedient to apply to ,parliament for a prolongation of the term1 and an ,act was passed in #agge granting an extension of twenty-five years from that date1 in consideration of the great merit of the invention4 7,bourne's ,treatise on the ,steam-engine47 ,in ,fig4 #cie 7p4 #dbg7 we give an illustration of a low-pressure condensing engine and boiler of eight-horse power1 constructed on the principle of ,boulton and ,watt1 as the latter had fortunately united his skill1 learning1 originality1 and experience with ,mr4 ,boulton1 of ,soho1 near ,birmingham1 whose metal manufactory was already the most celebrated in ,england4 ,during the explanation of this eight horse-power engine1 the opportunity may be taken to discuss occasionally the special improvements effected by ,watt4 ,the steam-pipe ,a conveys the steam generated in the boiler ,b to the slide-valve ,c1 which is kept close to the surface1 against which it works by the pressure of the steam4 ,here we notice some of the valuable improvements of ,watt in the admission of steam above as well as below the piston1 by which he increased the power of his engine1 and no longer confined it to the force of the atmospheric pressure4 ,it is also necessary to remark the beautifully simple mechanism of the slide-valve1 by which steam is admitted alternately above and below the piston4 ,want of space prevents us tracing out the gradual improvements effected by ,watt1 and therefore we take his invention as it stood in the year #aghj1 and refer our readers to ,bourne's ,treatise on the ,steam-engine for the full and minute particulars of the improvements to that date4 ,page #dbg ,illustration3 ,fig4 #cie4 ,an eight-horse power condensing steam-engine1 after the principle of ,boulton and ,watt1 and explained in pages #dbf to #dcb4 ,page #dbh ,at that time it occurred to ,watt that the condensation of the steam from the cylinder after it had done its work1 might be made more perfect if a perpetual vacuum was maintained beneath the piston1 while an alternate steam-pressure and vacuum were produced above it4 7,fig4 #cif47 ,illustration3 ,fig4 #cif4 ,e ,e is the cylinder4 ,j4 ,the piston1 a4 ,the steam-pipe4 b4 ,the regulating or throttle valve1 e4 ,the eduction and equilibrium single valve1 performing the functions of both4 c4 ,the upper1 and f the under1 portholes1 by which passages only the steam can enter and pass away4 d1 j1 g4 ,the eduction-pipe by which the steam passes from above the piston during every returning stroke to the condenser1 a perpetual exhaustion being maintained beneath it4--,from ,,bourne on the ,steam-engine4 ,instead of obtaining a specific advantage the contrary occurred1 and ,watt was obliged in this case to return to the ponderous ,newcomen counterweight to balance the difference in the vacuum above and below the piston1 consequently this form of the cylinder and valves was abandoned4 ,the juvenile reader will perceive in the above drawing that the superior arrangement of ,watt's cylinder to that of ,newcomen arises from the steam operating above and below the piston1 and that the piston rod works air-tight in a stuffing box at the top of the cylinder4 ,a most important improvement in the employment of steam as a motive power has been discovered in the mode of using it expansively1 by which the steam1 at a pressure say of sixty pounds on the square inch1 is admitted below the piston1 and then cut off and allowed to expand and drive up the latter without the expenditure of any more fuel1 and leaving1 after lifting the piston to a height say of three feet1 an average or mean power of thirty pounds on the square inch4 ,returning to the eight-horse condensing engine1 ,d is the steam cylinder surrounded by a case to prevent the steam cooling and to maintain in the ,page #dbi cylinder the same1 or nearly the same1 temperature as that of the steam in the boiler1 according to the condition of ,art4 ,i4 of ,watt's ,patent1 quoted at p4 #dbe of this book4 ,the same outer case is apparent around the cylinder in ,fig4 #cif2 ,e1 the piston1 which1 by stuffing with hemp or other proper material1 fits the interior of the cylinder in the most accurate manner1 and prevents the escape of steam by its sides3 e is the piston rod attached to the parallel motion4 ,this clockwork-like piece of mechanism has often been quoted as one of the masterpieces of ,watt1 and in its greatest perfection is called the complete parallel motion1 and may be found in all the best land beam steam-engines4 ,the object of the parallel motion is to cause the piston and pump rods to move always in straight lines1 never deviating to either side4 7,fig4 #cig47 ,illustration3 ,fig4 #cig4 ,a ,b is half the beam1 ,a being the main centre1 ,b ,e4 ,the main links connecting the piston-rod ,f with the end of the beam4 ,g ,d4 ,the air-pump links1 from the centre of which the air-pump rod is suspended4 ,c ,d and ,e ,d produce the parallelism1 because ,c ,d is moveable only round the fixed centre ,c1 whilst ,e ,d is not only moveable round the centre ,d1 but the centre itself in the arc described by ,c ,d1 and by this action ,e ,d corrects the distorting influence of its own radius4 ,the dotted lines and letters above enable the observer to see the effect of the movement of the beam on the parallel motion4 ,in the eight horse-power engine shown in page picture1 e is also attached to the piston ,e1 which moves the beam ,f1 and the other end of this beam1 by the connecting rod g1 gives motion to the heavy fly wheel ,g1 by means of the crank h4 ,h is an eccentric circle on the axle of the fly wheel ,g1 it gives motion to the slide valve1 which admits the steam alternately above and below the piston4 ,the slide valve and its seat are contained within an oblong box or case1 large enough to permit the easy motion of the valve within it1 and usually forming an enlargement in the course of a pipe4 ,the valve rod by means of which the valve is opened and shut1 passes out through a stuffing box2 or1 instead of such a rod1 a valve of moderate size often has a nut fixed to it1 within which works a screw on the end of an axle which passes out through a bush1 and has shoulders within and without to prevent it from moving longitudinally1 and a square on the outer end on which the key fits that is used in turning it4 ,i is the throttle valve inside the steam pipe and lever connected with a governor for regulating the admission of steam into the cylinder4 ,here1 again1 we pause in the description of our eight horse-power engine to illustrate more particularly this admirable contrivance of ,page #dcj ,watt1 which remains to the present day without any material alteration even in the best steam-engines4 7,fig4 #cih47 ,illustration3 ,fig4 #cih4 ,a4 ,the seat of the throttle valve1 ,z4 ,the valve itself turning on a spindle1 which passes through its centre4 a is the steam pipe4 w4 ,the throttle valve lever on which the rod ,h1 proceeding from the governor1 acts4 ,d ,d4 ,the spindle of the governor revolving by a belt acting on the pulley d4 ,e ,e4 ,the balls hung on the ends of the arms1 which cross each other at e like a pair of scissors4 ,when ,d ,d is set in motion1 the balls fly out by centrifugal motion1 and in doing so draw down the collar into which the lever ,f works by means of the links f h4 ,when ,f is depressed1 of course ,h rises1 and the valve ,z is partly closed1 and the supply of steam reduced4 ,in the eight-horse engine already partly explained1 k is the cylinder of an air-pump to remove any air1 and the water which condenses the steam1 from the condenser ,l4 ,there is also the eduction pipe1 which conducts the steam from the cylinder to the condenser ,l4 ,o is the pump that supplies cold water to the cistern ,s1 in which the condenser and air-pump stand1 ,p is a rod connected with the injection cock for admitting a jet of water into the condenser from the cistern1 and which is continually flowing during the working of the engine1 ,q ,q1 cast-iron columns1 four of which support the principal parts of the engine4 ,we now come to the boiler of the steam-engine1 which is of course of almost equal importance with the engine itself2 and the one in our page-picture is a good type of one of the favourite boilers used by ,messrs4 ,boulton and ,watt1 and is called the ,wagon boiler4 ,the boiler is made of wrought-iron plates rivetted together1 and properly strengthened where necessary2 and the steam-pipe ,a conveys the steam to the engine4 ,it may be remarked here that the cylindrical ,page #dca boiler--consisting of two cylinders1 one within the other1 of which the former contains the fire1 whilst the furnace-draught circulates outside the latter1 and the space between the two cylinders being filled with water--is the form of boiler which is most highly approved of1 and is employed in the famous economical steam-engines of the ,cornish mines4 ,as the water evaporates in the form of steam1 the boiler must be continually supplied with fresh water1 which comes 7as will be noticed by inspecting the page picture7 from the hot well ,s1 by means of the hot-water pump ,r1 attached to the beam ,f4 ,the water is pumped to the top of a column rising above but connected with the boiler4 ,there is a cylindrical float1 inside the column of water1 connected with the boiler1 suspended ever a pulley by a chain passing to the damper of the furnace4 ,the damper and float balance each other1 and when the water in the boiler rises to too high a temperature1 it causes the float to rise in the column of water1 which lowering the damper or shutter that stops the draught of the chimney of the furnace ,t1 diminishes the intensity of the heat1 and reduces the formation of steam4 ,on the other hand1 as the temperature diminishes1 the float descends and the damper rises1 and permitting more air to rush to the burning fuel in the fire1 a greater quantity of steam is generated4 ,there is likewise a stone float inside the boiler1 for regulating the supply of water by the feed pipe1 or column of water1 which latter must always be sufficiently lofty to press with greater force than the steam produced in the boiler1 or else the power of the steam might1 under certain circumstances1 eject or blow out the water from the top of the column4 ,the stone is suspended by a brass wire which works through a stuffing box1 and is connected with a lever1 to which is attached a heavy counterpoise1 so adjusted that when the stone is immersed to a certain depth in water 7according to the principle of a solid body losing weight in a fluid1 explained in the article on specific gravity1 page #dh71 it shall exactly balance the latter1 but when the water sinks in the boiler1 and the stone is no longer surrounded with water1 it becomes heavier1 and sinking down opens a conical plug1 ground so as to fit water-tight into a hole in the bottom of the column of water or feed pipe1 and directly the plug opens1 water rushes into the boiler2 being cut off again as the stone rises when immersed or surrounded with the proper height of water4 ,unless our juvenile readers refer to the article on specific gravity1 they will not understand the otherwise seeming anomaly of a stone float4 ,a large hole1 called the man-hole1 covered with an iron plate and securely fastened with screws1 is provided for the purpose of allowing the engineer to enter the boiler1 when cold1 for the purpose of clearing out the incrustation and dirt arising from the water4 ,to prevent the incrustation of lime and other earthy matters1 it is sometimes usual1 on the principle that prevention is better than cure to put a large log of logwood inside the boiler1 as it is found that the colouring matter curiously prevents the earthy matter1 so well known as the fur in iron tea-kettles1 sticking to the sides of the boiler4 ,sal ammoniac ,page #dcb and other salts also have the same property1 but neither are much used1 the mechanical labour of chipping out the boiler and stopping its work for a day or so1 being preferred to the prevention plan already described4 ,there is also a valve opening inwards to prevent the consequences of a sudden condensation in the boiler1 and also a safety valve and lever with weights opening outwards1 and allowing the steam to escape when it reaches a dangerous excess1 and in order to look as it were at the state of the pressure inside the iron boiler1 a proper steam gauge is provided1 also two cocks--viz41 a water and steam cock1 to enable the engineer to ascertain if the water is up to1 and does not exceed1 the proper height1 because when turned1 supposing that all is going on properly1 the former1 ,no4 #g1 should eject water1 the latter1 ,no4 #h1 steam4 ,it is truly wonderful1 considering the number of safeguards and warnings provided1 that accidents ever happen to boilers1 but the statistics of deaths and annual destruction of property show that science is powerless1 nay1 absolutely dangerous1 when handled by ignorant and careless persons4 ,the great fly-wheel1 which is usually such an awe-inspiring and marvellous exhibition of strength in an engine of any great power1 is employed for the purpose of storing up force1 so that if any parts of the engine work indifferently 7they all work with resistance71 it shall equalize the wants of the whole1 and by its inertia it will continue to move until its motion is stopped by a resistance equal to its momentum4 ,in starting an engine1 the engineer may sometimes be observed labouring to move the fly-wheel1 and when once he succeeds in getting it to move1 the resistance of the other parts of the machinery is soon overcome4 ,mr4 ,alderson1 in his prize essay1 remarks that it is in the property which the steam-engine possesses of regulating itself1 and providing for all its wants1 that the great beauty of the invention consists4 ,it has been said that nothing made by the hand of man approaches so near to animal life4 ,heat is the principle of its movement2 there is in its tubes circulation1 like that of the blood in the veins of animals1 having valves which open and shut in proper periods2 it feeds itself1 evacuates such portions of its food as are useless1 and draws from its own labours all that is necessary to its own subsistance4 ,to this may be added1 that they are now regulated so as not to exceed the assigned speed1 and thus do animals in a state of nature4 ,that the safety valves1 like the pores of perspiration1 open to permit the escape of superfluous heat in the form of steam4 ,the steam gauge1 as a pulse to the boiler1 indicates the heat and pressure of the steam within2 and the motion of the piston represents the action and the power of which it is capable4 ,the motion of the fluids in the boiler represents the expanding and collapsing of the heart2 the fluid that goes to it by one channel is drawn off by another1 in part to be returned when condensed by the cold1 similar to the operation of veins and arteries4 ,animals require long and frequent periods of relaxation from fatigue1 and any great accumulation of their power is not obtained without great expense and inconvenience4 ,the ,page #dcc wind is uncertain2 and water1 the constancy of which is in few places equal to the wants of the machinist1 can seldom be obtained on the spot where other circumstances require machines to be erected4 ,to relieve us from all these difficulties1 the last century has given us the steam-engine for a resource1 the power of which may be increased to infinitude3 it requires but little room2 it may be erected in all places1 and its mighty services are always at our command1 whether in winter or summer1 by day or by night1 on land or water2 it knows no intermission but what our wishes dictate4 ,the high-pressure steam-engine appears to have been first brought into general use by ,trevethic and ,vivian1 although the primary notion of such a modification of the ,newcomen or water-engines did not originate with them4 ,as the name implies1 the steam is brought to a much higher temperature and pressure than is required in the condensing engines of ,boulton and ,watt4 ,it consisted1 in the first place1 of a cylinder open at the top1 and provided with a piston4 ,to save heat the cylinder was fixed inside the boiler1 and was provided with a two-way cock worked by a crank1 for the purpose of supplying and cutting off the steam4 ,the downward stroke was produced by the atmosphere1 and the steam having done its work1 was simply blown away and wasted in the air4 ,the engine was provided with a fly-wheel1 to which the piston-rod was at once attached1 producing a continuous rotatory movement without the assistance of the heavier parallel motion1 or hot and cold water pumps4 ,this form of engine was soon adopted for pumping work--such as that of draining fens2 and in #ahjd ,mr4 ,richard ,trevethic used it for propelling the first carriage on the ,merthyr ,tydvil rail or tram way1 and it was then speedily adopted in all the coal districts where the levels were moderate4 ,stephenson the elder1 succeeded by the late lamented ,robert ,stephenson1 followed with inventions and improvements of the locomotive steam-engine2 and we are told in ,once a ,week that1 ,one of those best qualified to speak to the latter's contributions to the development of the locomotive engine1 states that from about five years from his return from ,america1 ,robert ,stephenson's attention was chiefly directed to its improvement4 ',none but those who accompanied him during the period in his incessant experiments can form an idea of the amazing metamorphosis which the machine underwent in it4 ,the most elementary principles of the application of heat1 of the mode of calculating the strength of cylindrical and other boilers1 of the strength of rivetting and of staying flat portions of the boilers1 were then far from being understood1 and each step in the improvement of the engine had to be confirmed by the most careful experiments before the brilliant results of the ,rocket and ,planet engines 7the latter being the type of the existing modern locomotive7 could be arrived at4' ,stephenson's time was not1 however1 so fully taken up during the above interval as to preclude attention to his other civil engineering business1 and he executed within it the ,leicester and ,swannington1 ,page #dcd ,whitby and ,pickering1 ,canterbury and ,whitstable1 and ,newton and ,warrington ,railways2 while he also erected an extensive manufactory for locomotives at ,newton1 in ,lancashire1 in partnership with the ,messrs4 ,tayleur4 ,about the middle of the above period1 also1 the first surveys and estimates for the ,london and ,birmingham ,railway were framed1 leading eventually to the obtaining of the ,act4 ,then followed the execution of that line1 and here ,robert ,stephenson had an opportunity of showing his great talent for the management of works on a large scale4 ,this was the first railway of any magnitude executed under the contract system2 perfect sets of plans and specifications 7which have since served as a type for nearly all the subsequent lines7 were prepared--no small matter for a series of works extending over #aab miles1 involving tunnels and other works of a then unprecedented magnitude4 ,many other railways in ,england and abroad were executed by him in rapid succession2 the ,midland1 ,blackwall1 ,northern and ,eastern1 ,norfolk1 ,chester and ,holyhead1 together with numerous branch lines1 were executed in this country by him2 and among railways abroad may be enumerated as works either executed by him or recommended in his capacity of a consulting engineer1 the system of lines in ,belgium1 ,italy1 ,norway1 and ,egypt1 and in ,france1 ,holland1 ,denmark1 ,india1 ,canada1 and ,new ,zealand4 ,robert ,stephenson first saw the light in the village of ,willington1 at a cottage which his father occupied after his marriage with ,miss ,fanny ,henderson--a marriage contracted on the strength of his first appointment as breaksman to the engine employed for lifting the ballast brought by the return collier ships to ,newcastle4 ,here ,robert was born on the #agth of ,november1 #ahjc4 ,as the cottage looked out upon a tramway1 the eyes of the child were naturally familiarized from infancy with sights and scenes most nearly connected with his future profession4 ,in locomotive steam-engine boilers1 the principal object is to generate steam with the greatest rapidity2 hence the boiler consists of two parts--viz41 a square box containing the fire1 and around which a thin stratum of water circulates1 whilst the draught for the fire rushes through a number of copper tubes placed in the second or cylindrical part of the boiler4 ,by the use of these tubes an immense surface of water is exposed to the action of the fire1 and the steam is not only generated with amazing rapidity1 but is also maintained at a very high pressure4 ,within the last few years superheated steam has been favourably mentioned1 and employed economically for driving certain engines4 ,the principle consists in first generating steam1 and then passing it through coils of strong wrought-iron pipe1 by which it acquires additional heat1 and we have therefore combined in steam the ordinary principle of evaporation of water with the heated-air principle of ,stirling1 described at p4 #cfg4 ,we give a drawing of ,scott's patent generator and superheated steam engine4 7,fig4 #cii47 ,the apparatus is used as follows3--,a fire is made in the furnace1 and so soon as a pyrometer connected with that indicates about #hjj degrees1 ,page #dce a little water is pumped into the coils by hand1 which is immediately converted into steam4 ,the donkey engine is then started1 which maintains the necessary feed of air and water4 ,the generator produces a copious supply of elastic mixed gaseous vapour1 at a pressure of #bej pounds on the square inch2 and it is stated that this engine works satisfactorily1 and is started in the incredibly short time of from three to five minutes1 so that for marine engines in war vessels1 expecting to be ordered out suddenly1 no fuel need be burnt till the moment required4 ,illustration3 ,fig4 #cii4 ,scott's patent generator1 or new versus old steam4 ,experiments with superheated steam have already been tried most successfully on board the ,peninsular and ,oriental ,company's ship the ,valetta1 whereby it is stated that a saving of thirty per cent4 in fuel ,page #dcf is obtained4 ,the engine to which the superheated steam was adapted was constructed by ,penn and ,sons1 and the vessel attained a speed of nearly sixteen knots per hour1 and under the most adverse circumstances had an abundance of steam to spare4 ,a most important experimental improvement in steam machinery was on ,thursday last tried for the first time down the river1 on board the ,peninsular and ,oriental ,company's ship1 the ,valetta4 ,the actual nature of the improvement may be described in a few words as consisting of a simple apparatus for working marine engines by means of superheated steam2 but it is not too much to say that in the success or failure of this experiment are involved results so important as to affect materially all ocean-going steamers1 and1 indeed1 steam machinery of all kinds4 ,to be able to work machinery with superheated steam1 means to command increased power with a thirty per cent4 reduction in the consumption of fuel4 ,a principle which can effect such important changes in the universal application of steam has not remained undiscovered to the present day4 ,the want of superheated steam has long been felt1 and the enormous comparative advantages of working engines on such a plan have long been known4 ,a simple and effective working of the principle1 however1 has been an engineering difficulty which various expedients--all1 however1 sufficiently successful to show the value of the improvement--have failed to obviate entirely4 ,this obstacle has now1 we believe1 been effectually overcome by ,mr4 ,penn1 and the value of the improvement so clearly demonstrated1 that the general application of the principle to steam machinery of every kind may now be regarded as certain4 ,the idea of working engines by superheated steam1 and the immense saving of fuel and increase of power it would effect1 was1 we believe1 first started many years ago by ,mr4 ,howard1 and subsequently by ,dr4 ,haycraft4 ,the difficulties1 however1 in the way of its adoption at that time1 and the undue estimate of the importance of the principle1 prevented those gentlemen from realizing very great practical results4 ,at a later period the matter was again taken up by an ,american engineer--,mr4 ,weatherhead--who1 however1 only superheated a portion of the steam and mixed it with common steam in its way to the cylinders4 ,the success which attended even this partial application of the process again revived the idea1 and encouraged other engineers to turn their attention to the subject4 ,the result of these renewed efforts is that several methods of securing the great economy to be effected by superheating the steam are now under trial1 and there is no doubt that a most important step in the progress of steam1 especially as applied to ocean navigation1 is now at last on the point of being successfully accomplished4 ,the value of the improvement on the score of economy in working may be best illustrated by a single fact--namely1 that the ,peninsular and ,oriental ,company's bill for coal annually amounts to the enormous sum of #gjj1jjjl41 and that by working their vessels with superheated steam properly applied1 it is become almost certain that1 without any ,page #dcg detriment to the machinery1 from #bh to #cj per cent4 of this gigantic outlay can be saved4 ,as to the various proposed methods of superheating steam1 it may be briefly explained1 that the conditions required to be fulfilled are perfect simplicity of arrangement with ready control over the apparatus2 that it should be so placed as not to be liable to accidental injury in the engine-room2 and that the heat employed for superheating the steam should be waste heat which has already done its duty in the boilers and is passing away4 ,all these conditions have been most satisfactorily fulfilled by ,mr4 ,penn in the new engines on board the ,valetta1 which were tried down the ,thames for the first time on ,thursday4 ,the ,valetta1 as our readers may remember1 was for many years the mail-boat between ,marseilles1 ,malta1 and ,constantinople4 ,while thus employed1 she had ,penn's engines of #djj horse-power1 and to work these up to an average speed of #ae miles an hour required a consumption of fuel of from #gj to #ge tons of coal per day4 ,at no time was it less than from #de to #ee tons4 ,these engines have now been removed to a vessel nearly double the tonnage of the ,valetta1 and the latter fitted with engines by ,mr4 ,penn on the superheating principle4 ,we may mention that1 besides this alteration1 the ,valetta has been considerably improved4 ,a poop and forecastle have been added1 increased accommodation given to passengers1 and the whole vessel fitted up in the richest style4 ,the saloon is one of the simplest and handsomest things of the kind we have seen1 sufficiently lofty and capacious1 and above all1 admirably ventilated on the system which is now being adopted on all sea-going steamers1 and the merit of devising which belongs to ,mr4 ,robinson1 of the ,peninsular and ,oriental ,company4 ,to return1 however1 to the engines4 ,mr4 ,penn1 at the repeated request of ,mr4 ,allen1 the ,managing ,director of the ,peninsular and ,oriental ,company1 undertook to apply to them the principle of superheating1 to which his attention had many years before been seriously directed by ,dr4 ,haycraft4 ,his method of doing this is to place in the smoke-box of the boiler1 through which the hot air from the furnace first passes1 as large a number of small pipes as is consistent with allowing a free draught from the furnaces4 ,through these all the steam from the boilers passes in its way to the cylinders4 ,by this plan an immense heating surface in the pipes is secured1 the steam is in a subdivided form1 so as to be readily acted on1 and the waste heat from the furnace is utilized at the point where its intensity is greatest1 and where the greatest conveniences exist for applying the apparatus4 ,by means of three ordinary stop-valves1 the whole contrivance can be shut in or off from the engines at pleasure4 ,in ordinary engines steam leaves the boilers at about #bej1 but declines from this temperature in its way to the engines to #bcj1 undergoing from condensation a still greater and more serious diminution of heat in the cylinders4 ,from these causes1 and also from the immense quantity of waste heat which escapes through the smoke-box and up the funnels1 there has always been a theoretical loss of steam power amounting to forty per cent41 as ,page #dch compared with the coal consumed4 ,it is this loss of power and waste of heat which the superheating process is intended to prevent1 and which will1 of course1 allow a reduction of from twenty-eight to thirty per cent4 on the fuel now consumed4 ,by the superheating process the steam is raised in passing along the pipes in the smoke-box 7where the heat is about #fej7 from a temperature of #bej to #cej1 and so enters the cylinders at #ajj in excess of the temperature due to its pressure4 ,this extra heat is1 of course1 rapidly communicated to the metals1 and prevents the condensation in the cylinders or other parts of the engines1 which would otherwise1 of course1 take place4 ,singularly enough1 a smaller amount of cold water is required to condense the steam at this high temperature of #cej than when at the ordinary heat of common steam4 ,the trial trip of the ,valetta on ,thursday was most satisfactory1 not only as regards the engines1 but still more so as to the application for the superheating process4 ,at the measured mile at the ,lower ,hope1 near the ,nore1 the result of repeated runs gave an average speed of nearly #ad knots per hour1 thus realizing with engines of #bfj horse-power1 and a small consumption of fuel1 the same rate of speed as had been gained with her previous engines of #djj horse-power1 and a consumption of seventy-five tons of coals per day4 ,the superheating apparatus evidently effected a most important saving in fuel1 but until an average of many days' working can be obtained1 it would be difficult to estimate the exact amount economized4 ,there seems1 however1 every reason to believe that an average of fourteen knots an hour can be obtained with a consumption of only from twenty-four to twenty-six tons per diem4 ,the thermometer during the trial indicated in the steam pipes an addition to the ordinary temperature of #ajj1 which ,mr4 ,penn believes to be enough for all practical purposes of superheating4 ,even when making from thirty-three to thirty-four revolutions per minute1 and driving the vessel against a strong head wind and tide1 it was impossible to consume all the steam generated1 which was blowing off from both boilers all the trip4 ,the engines are remarkable for the extraordinary beauty and simplicity of their proportions1 qualities well known in all engines from ,penn and ,sons1 and which1 combined with the strength of the materials and perfection of the workmanship1 make this firm the foremost in the world for machinery of this description4 ,both cylinders are oscillating1 of sixty-two inches diameter1 and with a stroke of four feet six inches4 ,the paddles are on the feathering principle1 and the boilers of ,lamb and ,co4's patent4 ,during the whole course of the trials1 and when going at one time nearly sixteen knots1 there was no perceptible vibration1 even at the end of the saloon nearest to the engines4 ,when it is remembered that the superheating process which can effect such important results is capable1 as we have said1 of application to steam machinery of every kind1 including even locomotives1 it cannot be doubted that the trial of ,thursday and its great success is one of the most important events for the progress of steam which we have had to chronicle for many years4 7,the ,times1 ,april #bcrd4 #ahei47 ,page #dci ,whilst speaking of the application of this somewhat novel condition of steam1 it may be observed that many inventors1 who have paid little or no attention to first principles1 have proposed to apply the vapours of alcohol1 ether1 or turpentine1 instead of that of water2 and they have founded their notions on the idea that in consequence of the less latent and sensible heat of alcohol1 ether1 and turpentine vapour1 and of the small quantity of fuel required to boil them1 that they would compete advantageously with steam4 ,this view of the case1 however1 is soon proved to be a very shortsighted one1 because the amount of expansion has been quite overlooked2 and if it was desirable1 by way of comparison1 to produce a cubic foot of steam1 alcohol1 ether1 or turpentine1 the steam would stand first for cheapness1 and would require the least quantity of fuel to produce it1 so that if the more expensive of combustible liquids could be obtained for nothing1 it would still be cheaper to employ water4 ,latent heat1 or equivalent for fuel4 ,a cubic foot of water yields #agjj cubic feet of steam #ajjj ,a cubic foot of alcohol produces #dic cubic feet #deg4 ,then1 by rule of proportion1 #dic cubic inches 3 #deg 33 #agjj 3 #aege ,a cubic foot of ether yields only #bab cubic feet of vapour #cab1 and #bab 3 #cab 33 #agjj 3 #bejj ,a cubic foot of the oil of turpentine affords #aib cubic feet of vapour #ahc1 and #aib 3 #ahc 33 #agjj 3 #afbj ,it will therefore be seen that water1 when converted into steam1 expands eight times as much as sulphuric ether1 and nearly three times and a half as much as alcohol4 ,the application of steam for the purpose of propelling vessels has already been mentioned in connexion with the ,spanish inventor1 ,blasco de ,garay1 in the year #aedc4 ,the first patent in this kingdom granted for that purpose was that of ,mr4 ,jonathan ,hull in #aggc4 ,in #aghg1 ,mr4 ,miller tried a number of important experiments in the propulsion of vessels by steam-engines1 and it would appear that ,lord ,cullen advocated his ideas1 and endeavoured to secure the co-operation of the great firm of ,boulton and ,watt1 who1 occupied with their land engines1 could not pay attention to it2 and twenty years elapsed after the reply of ,watt to ,lord ,cullen's application1 before the real novelty appeared of a first successful experiment with a steam-boat in the open sea1 by ,henry ,bell1 in #ahaa4 ,a picture of this boat1 called the ,comet1 which was afterwards wrecked1 is shown at p4 #dah4 ,henry ,bell's novelty was success1 and he is fairly entitled to the merit of first introducing steam navigation into ,europe4 ,in #ahaa1 the public stared with mingled astonishment and satisfaction at the realization of that which was called a fable4 ,only forty-seven years afterwards another generation spontaneously exhibits the liveliest interest in the gigantic private speculation of the ,great ,eastern4 ,page #ddj ,henry ,bell's vessel of #ahaa was #dj feet keel1 #aj feet #f inches beam1 and #be tons burthen6 ,the ,great ,eastern of #ahei is #fib feet long1 #hc feet wide1 #fj feet deep1 and #bd1jjj tons burthen66 ,the whole nation with one voice wish her ,god speed in her projected voyage across the ,atlantic1 as the embodiment of that great goodwill which every generous-hearted ,englishman feels towards the enlightened free-born people of the ,united ,states4 ,should the author's little vessel1 with its humble freight of science1 meet with the approbation of his good friends1 the boys and their advisers1 another and another1 if health permits1 shall be launched for their benefit4 ,vale4 ,illustration ,,the ,,end4 ,transcriber's ,notes4 ,words and phrases in italics are indicated with underscores thus3- italics4 ,chapter ,,xv4 ,experiment one is not indicated by a title heading4 ,page #ii4 the pulse is raised forty or fifty beats per second changed to the pulse is raised forty or fifty beats per minute ,page #adh4 it is allowed to dry spontaneously1 and being coated with amber varnish 7a solution of amber in chloroform7 is now ready to print from4 ,it is1 perhaps1 hardly necessary to add1 that the sensitizing and developing processes must be performed in a dark room4 ,fig4 #abc4 is irrelevant to this section4 ,the reference has been deleted4 ,page #cfe4 an air thermometer has been employed by ,sir ,john ,leslie1 under the name of the ,differential ,thermometer1 in his refined and delicate experiments with heat4 7,fig4 #dja47 ,ref4 to 7,fig4 #dja47 removed4 ,fig4 #dja4 not in original hard copy version4