,,the ,,story ,,of ,,electricity ,,by ,,john ,,munro ,,author ,,of ,,electricity ,,and ,,its ,,uses1 ,,pioneers ,,of ,,electricity1 ,,heroes ,,of ,,the ,,telegraph1 ,,etc41 ,,and ,,joint ,,author ,,of ,,munro ,,and ,,jamieson',s ,,pocket-,,book ,,of ,,electrical ,,rules ,,and ,,tables ,,preface4 ,a work on electricity needs little recommendation to stimulate the interest of the general reader4 ,electricity in its manifold applications is so large a factor in the comfort and convenience of our daily life1 so essential to the industrial organization which embraces every dweller in a civilized land1 so important in the development and extension of civilization itself1 that a knowledge of its principles and the means through which they are directed to the service of mankind should be a part of the mental equipment of everyone who pretends to education in its truest sense4 ,let anyone stop to consider how he individually would be affected if all electrical service were suddenly to cease1 and he cannot fail to appreciate the claims of electricity to attentive study4 ,the purpose of this little book is to present the essential facts of electrical science in a popular and interesting way1 as befits the scheme of the series to which it belongs4 ,electrical phenomena have been observed since the first man viewed one of the most spectacular and magnificent of them all in the thunderstorm1 but the services of electricity which we enjoy are the product solely of scientific achievement in the nineteenth century4 ,it is to these services that the main part of the following discussion is devoted4 ,the introductory chapters deal with various sources of electrical energy1 in friction1 chemical action1 heat and magnetism4 ,the rest of the book describes the applications of electricity in electroplating1 communication by telegraph1 telephone1 and wireless telegraphy1 the production of light and heat1 the transmission of power1 transportation over rails and in vehicles1 and the multitude of other uses4 ,july1 #aiae4 ,,publishers' ,,note4 ,for our edition of this work the terminology has been altered to conform with ,american usage1 some new matter has been added1 and a few of the cuts have been changed and some new ones introduced1 in order to adapt the book fully to the practical requirements of ,american readers4 ,,contents4 ,i4 ,,the ,,electricity ,,of ,,friction ,,ii4 ,,the ,,electricity ,,of ,,chemistry ,,iii4 ,,the ,,electricity ,,of ,,heat ,,iv4 ,,the ,,electricity ,,of ,,magnetism ,v4 ,,electrolysis ,,vi4 ,,the ,,telegraph ,,and ,,telephone ,,vii4 ,,electric ,,light ,,and ,,heat ,,viii4 ,,electric ,,power ,,ix4 ,,minor ,,uses ,,of ,,electricity ,x4 ,,the ,,wireless ,,telegraph ,,xi4 ,,electro-,,chemistry ,,and ,,electro-,,metallurgy ,,xii4 ,,electric ,,railways ,,appendix ,,the ,,story ,,of ,,electricity4 ,,chapter ,i4 ,,the ,,electricity ,,of ,,friction4 ,a schoolboy who rubs a stick of sealing-wax on the sleeve of his jacket1 then holds it over dusty shreds or bits of straw to see them fly up and cling to the wax1 repeats without knowing it the fundamental experiment of electricity4 ,in rubbing the wax on his coat he has electrified it1 and the dry dust or bits of wool are attracted to it by reason of a mysterious process which is called induction4 ,electricity1 like fire1 was probably discovered by some primeval savage4 ,according to ,humboldt1 the ,indians of the ,orinoco sometimes amuse themselves by rubbing certain beans to make them attract wisps of the wild cotton1 and the custom is doubtless very old4 ,certainly the ancient ,greeks knew that a piece of amber had when rubbed the property of attracting light bodies4 ,thales of ,miletus1 wisest of the ,seven ,sages1 and father of ,greek philosophy1 explained this curious effect by the presence of a soul in the amber1 whatever he meant by that4 ,thales flourished #fjj years before the ,christian era1 while ,croesus reigned in ,lydia1 and ,cyrus the ,great1 in ,persia1 when the renowned ,solon gave his laws to ,athens1 and ,necos1 ,king of ,egypt1 made war on ,josiah1 ,king of ,judah1 and after defeating him at ,megiddo1 dedicated the corslet he had worn during the battle to ,apollo ,didymaeus in the temple of ,branchidas1 near ,miletus4 ,amber1 the fossil resin of a pine tree1 was found in ,sicily1 the shores of the ,baltic1 and other parts of ,europe4 ,it was a precious stone then as now1 and an article of trade with the ,phoenicians1 those early merchants of the ,mediterranean4 ,the attractive power might enhance the value of the gem in the eyes of the superstitious ancients1 but they do not seem to have investigated it1 and beyond the speculation of ,thales1 they have told us nothing more about it4 ,towards the end of the sixteenth century ,dr4 ,gilbert of ,colchester1 physician to ,queen ,elizabeth1 made this property the subject of experiment1 and showed that1 far from being peculiar to amber1 it was possessed by sulphur1 wax1 glass1 and many other bodies which he called electrics1 from the ,greek word elektron1 signifying amber4 ,this great discovery was the starting-point of the modern science of electricity4 ,that feeble and mysterious force which had been the wonder of the simple and the amusement of the vain could not be slighted any longer as a curious freak of nature1 but assuredly none dreamt that a day was dawning in which it would transform the world4 ,otto von ,guericke1 burgomaster of ,magdeburg1 was the first to invent a machine for exciting the electric power in larger quantities by simply turning a ball of sulphur between the bare hands4 ,improved by ,sir ,isaac ,newton and others1 who employed glass rubbed with silk1 it created sparks several inches long4 ,the ordinary frictional machine as now made is illustrated in figure i1 where ,p is a disc of plate glass mounted on a spindle and turned by hand4 ,rubbers of silk ,r1 smeared with an amalgam of mercury and tin1 to increase their efficiency1 press the rim of the plate between them as it revolves1 and a brass conductor ,c1 insulated on glass posts1 is fitted with points like the teeth of a comb1 which1 as the electrified surface of the plate passes by1 collect the electricity and charge the conductor with positive electricity4 ,machines of this sort have been made with plates #g feet in diameter1 and yielding sparks nearly #b feet long4 ,the properties of the electric fire1 as it was now called1 were chiefly investigated by ,dufay4 ,to refine on the primitive experiment let us replace the shreds by a pithball hung from a support by a silk thread1 as in figure #b4 ,if we rub the glass rod vigorously with a silk handkerchief and hold it near1 the ball will fly toward the rod4 ,similarly we may rub a stick of sealing wax1 a bar of sulphur1 indeed1 a great variety of substances1 and by this easy test we shall find them electrified4 ,glass rubbed with glass will not show any sign of electrification1 nor will wax rubbed on wax2 but when the rubber is of a different material to the thing rubbed1 we shall find1 on using proper precautions1 that electricity is developed4 ,in fact1 the property which was once thought peculiar to amber is found to belong to all bodies4 ,,any ,,substance1 ,,when ,,rubbed ,,with ,a ,,different ,,substance1 ,,becomes ,,electrified4 ,the electricity thus produced is termed frictional electricity4 ,of course there are some materials1 such as amber1 glass1 and wax1 which display the effect much better than others1 and hence its original discovery4 ,in dry frosty weather the friction of a tortoise-shell comb will electrify the hair and make it cling to the teeth4 ,sometimes persons emit sparks in pulling off their flannels or silk stockings4 ,the fur of a cat1 or even of a garment1 stroked in the dark with a warm dry hand will be seen to glow1 and perhaps heard to crackle4 ,during winter a person can electrify himself by shuffling in his slippers over the carpet1 and light the gas with a spark from his finger4 ,glass and sealing-wax are1 however1 the most convenient means for investigating the electricity of friction4 ,a glass rod when rubbed with a silk handkerchief becomes1 as we have seen1 highly electric1 and will attract a pithball 7fig4 #b74 ,moreover1 if we substitute the handkerchief for the rod it will also attract the ball 7fig4 #c74 ,clearly1 then1 the handkerchief which rubbed the rod as well as the rod itself is electrified4 ,at first we might suppose that the handkerchief had merely rubbed off some of the electricity from the rod1 but a little investigation will soon show that is not the case4 ,if we allow the pithball to touch the glass rod it will steal some of the electricity on the rod1 and we shall now find the ball ,,repelled by the rod1 as illustrated in figure #d4 ,then1 if we withdraw the rod and bring forward the handkerchief1 we shall find the ball ,,attracted by it4 ,evidently1 therefore1 the electricity of the handkerchief is of a different kind from that of the rod4 ,again1 if we allow the ball to touch the handkerchief and rub off some of its electricity1 the ball will be ,,repelled by the handkerchief and ,,attracted by the rod4 ,thus we arrive at the conclusion that whereas the glass rod is charged with one kind of electricity1 the handkerchief which rubbed it is charged with another kind1 and1 judging by their contrary effects on the charged ball or indicator1 they are of opposite kinds4 ,to distinguish the two sorts1 one is called ,,positive and the other ,,negative electricity4 ,further experiments with other substances will show that sometimes the rod is negative while the rubber is positive4 ,thus1 if we rub the glass rod with cat's fur instead of silk1 we shall find the glass negative and the fur positive4 ,again1 if we rub a stick of sealing-wax with the silk handkerchief1 we shall find the wax negative and the silk positive4 ,but in every case one is the opposite of the other1 and moreover1 an equal quantity of both sorts of electricity is developed1 one kind on the rod and the other on the rubber4 ,hence we conclude that ,,equal ,,and ,,opposite ,,quantities ,,of ,,electricity ,,are ,,simultaneously ,,developed ,,by ,,friction4 ,if any two of the following materials be rubbed together1 that higher in the list becomes positively and the other negatively electrified3-- ,,positive 774 ,cats' fur4 ,polished glass4 ,wool4 ,cork1 at ordinary temperature4 ,coarse brown paper4 ,cork1 heated4 ,white silk4 ,black silk4 ,shellac4 ,rough glass4 ,,negative 7-74 ,the list shows that quality1 as well as kind1 of material affects the production of electricity4 ,thus polished glass when rubbed with silk is positive1 whereas rough glass is negative4 ,cork at ordinary temperature is positive when rubbed with hot cork4 ,black silk is negative to white silk1 and it has been observed that the best radiator and absorber of light and heat is the most negative4 ,black cloth1 for instance1 is a better radiator than white1 hence in the ,arctic regions1 where the body is much warmer than the surrounding air1 many wild animals get a white coat in winter1 and in the tropics1 where the sunshine is hotter than the body1 the ,european dons a white suit4 ,the experiments of figures #a1 #b1 and #c have also shown us that when the pithball is charged with the positive electricity of the glass rod it is ,,repelled by the like charge upon the rod1 and ,,attracted by the negative or unlike charge on the handkerchief4 ,again1 when it is charged with the negative electricity of the handkerchief it is ,,repelled by the like charge on the handkerchief and ,,attracted by the positive or unlike charge on the rod4 ,therefore it is usual to say that ,,like ,,electricities ,,repel ,,and ,,unlike ,,electricities ,,attract ,,each ,,other4 ,we have said that all bodies yield electricity under the friction of dissimilar bodies2 but this cannot be proved for every body by simply holding it in one hand and rubbing it with the excitor1 as may be done in the case of glass4 ,for instance1 if we take a brass rod in the hand and apply the rubber vigorously1 it will fail to attract the pithball1 for there is no trace of electricity upon it4 ,this is because the metal differs from the glass in another electrical property1 and they must therefore be differently treated4 ,brass1 in fact1 is a conductor of electricity and glass is not4 ,in other words1 electricity is conducted or led away by brass1 so that1 as soon as it is generated by the friction1 it flows through the hand and body of the experimenter1 which are also conductors1 and is lost in the ground4 ,glass on the other hand1 is an ,,insulator1 and the electricity remains on the surface of it4 ,if1 however1 we attach a glass handle to the rod and hold it by that whilst rubbing it1 the electricity cannot then escape to the earth1 and the brass rod will attract the pith-ball4 ,all bodies are conductors of electricity in some degree1 but they vary so enormously in this respect that it has been found convenient to divide them into two extreme classes--conductors and insulators4 ,these run into each other through an intermediate group1 which are neither good conductors nor good insulators4 ,the following are the chief examples of these classes3-- ,,conductors4--,all the metals1 carbon4 ,,intermediate 7bad conductors and bad insulators74--,water1 aqueous solutions1 moist bodies2 wood1 cotton1 hemp1 and paper in any but a dry atmosphere2 liquid acids1 rarefied gases4 ,,insulators4--,paraffin 7solid or liquid71 ozokerit1 turpentine1 silk1 resin1 sealing-wax or shellac1 india-rubber1 gutta-percha1 ebonite1 ivory1 dry wood1 dry glass or porcelain1 mica1 ice1 air at ordinary pressures4 ,it is remarkable that the best conductors of electricity1 that is to say1 the substances which offer least resistance to its passage1 for instance the metals1 are also the best conductors of heat1 and that insulators made red hot become conductors4 ,air is an excellent insulator1 and hence we are able to perform our experiments on frictional electricity in it4 ,we can also run bare telegraph wires through it1 by taking care to insulate them with glass or porcelain from the wooden poles which support them above the ground4 ,water1 on the other hand1 is a partial conductor1 and a great enemy to the storage or conveyance of electricity1 from its habit of soaking into porous metals1 or depositing in a film of dew on the cold surfaces of insulators such as glass1 porcelain1 or ebonite4 ,the remedy is to exclude it1 or keep the insulators warm and dry1 or coat them with shellac varnish1 wax1 or paraffin4 ,submarine telegraph wires running under the sea are usually insulated from the surrounding water by india-rubber or gutta-percha4 ,the distinction between conductors and non-conductors or insulators was first observed by ,stephen ,gray1 a pensioner of the ,charter-house4 ,gray actually transmitted a charge of electricity along a pack-thread insulated with silk1 to a distance of several hundred yards1 and thus took an important step in the direction of the electric telegraph4 ,it has since been found that ,,frictional ,,electricity ,,appears ,,only ,,on ,,the ,,external ,,surface ,,of ,,conductors4 ,this is well shown by a device of ,faraday resembling a small butterfly net insulated by a glass handle 7fig4 #e74 ,if the net be charged it is found that the electrification is only outside1 and if it be suddenly drawn outside in1 as shown by the dotted line1 the electrification is still found outside1 proving that the charge has shifted from the inner to the outer surface4 ,in the same way if a hollow conductor is charged with electricity1 none is discoverable in the interior4 ,moreover1 its distribution on the exterior is influenced by the shape of the outer surface4 ,on a sphere or ball it is evenly distributed all round1 but it accumulates on sharp edges or corners1 and most of all on points1 from which it is easily discharged4 ,a neutral body can1 as we have seen 7fig4 #d71 be charged by ,,contact with an electrified body3 but it can also be charged by ,,induction1 or the influence of the electrified body at a distance4 ,thus if we electrify a glass rod positively 77 and bring it near a neutral or unelectrified brass ball1 insulated on a glass support1 as in figure #f1 we shall find the side of the ball next the rod no longer neutral but negatively electrified 7-71 and the side away from the rod positively electrified 774 ,if we take away the rod again the ball will return to its neutral or non-electric state1 showing that the charge was temporarily induced by the presence of the electrified rod4 ,again1 if1 as in figure #g1 we have two insulated balls touching each other1 and bring the rod up1 that nearest the rod will become negative and that farthest from it positive4 ,it appears from these facts that electricity has the power of disturbing or decomposing the neutral state of a neighbouring conductor1 and attracting the unlike while it repels the like induced charge4 ,hence1 too1 it is that the electrified amber or sealing-wax is able to attract a light straw or pithball4 ,the effect supplies a simple way of developing a large amount of electricity from a small initial charge4 ,for if in figure #f the positive side of the ball be connected for a moment to earth by a conductor1 its positive charge will escape1 leaving the negative on the ball1 and as there is no longer an equal positive charge to recombine with it when the exciting rod is withdrawn1 it remains as a negative charge on the ball4 ,similarly1 if we separate the two balls in figure #g1 we gain two equal charges--one positive1 the other negative4 ,these processes have only to be repeated by a machine in order to develop very strong charges from a feeble source4 ,faraday saw that the intervening air played a part in this action at a distance1 and proved conclusively that the value of the induction depended on the nature of the medium between the induced and the inducing charge4 ,he showed1 for example1 that the induction through an intervening cake of sulphur is greater than through an equal thickness of air4 ,this property of the medium is termed its ,,inductive ,,capacity4 ,the ,electrophorus1 or carrier of electricity1 is a simple device for developing and conveying a charge on the principle of induction4 ,it consists1 as shown in figure #h1 of a metal plate ,b having an insulating handle of glass ,h1 and a flat cake of resin or ebonite ,r4 ,if the resin is laid on a table and briskly rubbed with cat's fur it becomes negatively electrified4 ,the brass plate is then lifted by the handle and laid upon the cake4 ,it touches the electrified surface at a few points1 takes a minute charge from these by contact4 ,the rest of it1 however1 is insulated from the resin by the air4 ,in the main1 therefore1 the negative charge of the resin is free to induce an opposite or positive charge on the lower surface and a negative charge on the upper surface of the plate4 ,by touching this upper surface with the finger1 as shown in figure #h1 the negative charge will escape through the body to the ground or earth1 as it is technically called1 and the positive charge will remain on the plate4 ,we can withdraw it by lifting the plate1 and prove its existence by drawing a spark from it with the knuckle4 ,the process can be repeated as long as the negative charge continues on the resin4 ,these tiny sparks from the electrophorus1 or the bigger discharges of an electrical machine1 can be stored in a simple apparatus called a ,leyden jar1 which was discovered by accident4 ,one day ,cuneus1 a pupil of ,muschenbroeck1 professor in the ,university of ,leyden1 was trying to charge some water in a glass bottle by connecting it with a chain to the sparkling knob of an electrical machine4 ,holding the bottle in one hand1 he undid the chain with the other1 and received a violent shock which cast the bottle on the floor4 ,muschenbroeck1 eager to verify the phenomenon1 repeated the experiment1 with a still more lively and convincing result4 ,his4 nerves were shaken for two days1 and he afterwards protested that he would not suffer another shock for the whole kingdom of ,france4 ,the ,leyden jar is illustrated in figure #i1 and consists in general of a glass bottle partly coated inside and out with tinfoil ,f1 and having a brass knob ,k connecting with its internal coat4 ,when the charged plate or conductor of the electrophorus touches the knob the inner foil takes a positive charge1 which induces a negative charge in the outer foil through the glass4 ,the corresponding positive charge induced at the same time escapes through the hand to the ground or earth4 ,the inner coating is now positively and the outer coating negatively electrified1 and these two opposite charges bind or hold each other by mutual attraction4 ,the bottle will therefore continue charged for a long time2 in short1 until it is purposely discharged or the two electricities combine by leakage over the surface of the glass4 ,to discharge the jar we need only connect the two foils by a conductor1 and thus allow the separated charges to combine4 ,this should be done by joining the ,,outer to the ,,inner coat with a stout wire1 or1 better still1 the discharging tongs ,t1 as shown in the figure4 ,otherwise1 if the tongs are first applied to the inner coat1 the operator will receive the charge through his arms and chest in the manner of ,cuneus and ,muschenbroeck4 ,leyden jars can be connected together in batteries1 so as to give very powerful effects4 ,one method is to join the inner coat of one to the outer coat of the next4 ,this is known as connecting in series1 and gives a very long spark4 ,another method is to join the inner coat of one to the inner coat of the next1 and similarly all the outer coats together4 ,this is called connecting in parallel1 or quantity1 and gives a big1 but not a long spark4 ,of late years the principle of induction1 which is the secret of the ,leyden jar and electrophorus1 has been applied in constructing influence machines for generating electricity4 ,perhaps the most effective of these is the ,wimshurst1 which we illustrate in figure #aj1 where ,,pp are two circular glass plates which rotate in opposite directions on turning the handle4 ,on the outer rim of each is cemented a row of radial slips of metal at equal intervals4 ,the slips at opposite ends of a diameter are connected together twice during each revolution of the plates by wire brushes ,s1 and collecting combs ,,tt serve to charge the positive and negative conductors ,,cc1 which yield very powerful sparks at the knobs ,k above4 ,the given theory of this machine may be open to question1 but there can be no doubt of its wonderful performance4 ,a small one produces a violent spark #h or #aj inches long after a few turns of the handle4 ,the electricity of friction is so unmanageable that it has not been applied in practice to any great extent4 ,in #agec ,mr4 ,charles ,morrison1 of ,greenock1 published the first plan of an electric telegraph in the ,scots ,magazine1 and proposed to charge an insulated wire at the near end so as to make it attract printed letters of the alphabet at the far end4 ,sir ,francis ,ronalds also invented a telegraph actuated by this kind of electricity1 but neither of these came into use4 ,morrison1 an obscure genius1 was before his age1 and ,ronalds was politely informed by the ,government of his day that telegraphs of any kind were wholly unnecessary4 ,little instruments for lighting gas by means of the spark are1 however1 made1 and the noxious fumes of chemical and lead works are condensed and laid by the discharge from the ,wimshurst machine4 ,the electricity shed in the air causes the dust and smoke to adhere by induction and settle in flakes upon the sides of the flues4 ,perhaps the old remark that smuts or blacks falling to the ground on a sultry day are a sign of thunder is traceable to a similar action4 ,the most important practical result of the early experiments with frictional electricity was ,benjamin ,franklin's great discovery of the identity of lightning and the electric spark4 ,one day in ,june1 #agib1 he went to the common at ,philadelphia and flew a kite beneath a thundercloud1 taking care to insulate his body from the cord4 ,after a shower had wetted the string and made it a conductor1 he was able to draw sparks from it with a key and to charge a ,leyden jar4 ,the man who had robbed ,jupiter of his thunderbolts became celebrated throughout the world1 and lightning rods or conductors for the protection of life and property were soon brought out4 ,these1 in their simplest form1 are tapes or stranded wires of iron or copper attached to the walls of the building4 ,the lower end of the conductor is soldered to a copper plate buried in the moist subsoil1 or1 if the ground is rather dry1 in a pit containing coke4 ,sometimes it is merely soldered to the water mains of the house4 ,the upper end rises above the highest chimney1 turret1 or spire of the edifice1 and branches into points tipped with incorrosive metal1 such as platinum4 ,it is usual to connect all the outside metal of the house1 such as the gutters and finials to the rod by means of soldered joints1 so as to form one continuous metallic network or artery for the discharge4 ,when a thundercloud charged with electricity passes over the ground1 it induces a charge of an opposite kind upon it4 ,the cloud and earth with air between are analogous to the charged foils of the ,leyden jar separated by the glass4 ,the two electricities of the jar1 we know1 attract each other1 and if the insulating glass is too weak to hold them asunder1 the spark will pierce it4 ,similarly1 if the insulating air cannot resist the attraction between the thundercloud and the earth1 it will be ruptured by a flash of lightning4 ,the metal rod1 however1 tends to allow the two charges of the cloud and earth to combine quietly or to shunt the discharge past the house4 ,,chapter ,,ii4 ,,the ,,electricity ,,of ,,chemistry4 ,a more tractable kind of electricity than that of friction was discovered at the beginning of the present century4 ,the story goes that some edible frogs were skinned to make a soup for ,madame ,galvani1 wife of the professor of anatomy in the ,university of ,bologna1 who was in delicate health4 ,as the frogs were lying in the laboratory of the professor they were observed to twitch each time a spark was drawn from an electrical machine that stood by4 ,a similar twitching was also noticed when the limbs were hung by copper skewers from an iron rail4 ,galvani thought the spasms were due to electricity in the animal1 and produced them at will by touching the nerve of a limb with a rod of zinc1 and the muscle with a rod of copper in contact with the zinc4 ,it was proved1 however1 by ,alessanjra ,volta1 professor of physics in the ,university of ,pavia1 that the electricity was not in the animal but generated by the contact of the two dissimilar metals and the moisture of the flesh4 ,going a step further1 in the year #ahjj he invented a new source of electricity on this principle1 which is known as ,volta's pile4 ,it consists of plates or discs of zinc and copper separated by a wafer of cloth moistened with acidulated water4 ,when the zinc and copper are joined externally by a wire1 a ,,current of electricity is found in the wire ,one pair of plates with the liquid between makes a couple or element2 and two or more1 built one above another in the same order of zinc1 copper1 zinc1 copper1 make the pile4 ,the extreme zinc and copper plates1 when joined by a wire1 are found to deliver a current4 ,this form of the voltaic1 or1 as it is sometimes called1 galvanic battery1 has given place to the cell shown in figure ,,ii1 where the two plates ,z ,c are immersed in acidulated water within the vessel1 and connected outside by the wire ,w4 ,the zinc plate has a positive and the copper a negative charge4 ,the positive current flows from the zinc to the copper inside the cell and from the copper to the zinc outside the cell1 as shown by the arrows4 ,it thus makes a complete round1 which is called the voltaic circuit1 and if the circuit is broken anywhere it will not flow at all4 ,the positive electricity of the zinc appears to traverse the liquid to the copper1 from which it flows through the wire to the zinc4 ,the effect is that the end of the wire attached to the copper is positive 771 and called the positive pole or electrode1 while the end attached to the zinc is negative 7-71 and called the negative pole or electrode4 ,a simple and easy way to avoid confusion as to the direction of the current1 is to remember that the ,,positive current flows ,,from the ,,copper ,,to the ,,zinc at the point of ,,metallic contact4 ,the generation of this current is accompanied by chemical action in the cell4 ,experiment shows that the mere ,,contact of dissimilar materials1 such as copper and zinc1 electrifies them--zinc being positive and copper negative2 but contact alone does not yield a continuous current of electricity4 ,when we plunge the two metals1 still in contact1 either directly or through a wire1 into water preferably acidulated1 a chemical action is set up1 the water is decomposed1 and the zinc is consumed4 ,water1 as is well known1 consists of oxygen and hydrogen4 ,the oxygen combines with the zinc to form oxide of zinc1 and the hydrogen is set free as gas at the surface of the copper plate4 ,so long as this process goes on1 that is to say1 as long as there is zinc and water left1 we get an electric current in the circuit4 ,the existence of such a current may be proved by a very simple experiment4 ,place a penny above and a dime below the tip of the tongue1 then bring their edges into contact1 and you will feel an acid taste in the mouth4 ,figure #ab illustrates the supposed chemical action in the cell4 ,on the left hand are the zinc and copper plates 7,z ,c7 disconnected in the liquid4 ,the atoms of zinc are shown by small circles2 the molecules of water1 that is1 oxygen1 and hydrogen 7,h#b,o7 by lozenges of unequal size4 ,on the right hand the plates are connected by a wire outside the cell2 the current starts1 and the chemical action begins4 ,an atom of zinc unites with an atom of oxygen1 leaving two atoms of hydrogen thus set free to combine with another atom of oxygen1 which in turn frees two atoms of hydrogen4 ,this interchange of atoms goes on until the two atoms of hydrogen which are freed last abide on the surface of the copper4 ,the contact electricity of the zinc and copper probably begins the process1 and the chemical action keeps it up4 ,oxygen1 being an electro-negative element in chemistry1 is attracted to the zinc1 and hydrogen1 being electro-positive1 is attracted to the copper4 ,the difference of electrical condition or potential between the plates by which the current is started has been called the electromotive force1 or force which puts the electricity in motion4 ,the obstruction or hindrance which the electricity overcomes in passing through its conductor is known as the ,,resistance4 ,obviously the higher the electromotive force and the lower the resistance1 the stronger will be the current in the conductor4 ,hence it is desirable to have a cell which will give a high electromotive force and a low internal resistance4 ,voltaic cells are grouped together in the mode of ,leyden jars4 ,figure #ac shows how they are joined in series1 the zinc or negative pole of one being connected by wire to the copper or positive pole of the next4 ,this arrangement multiplies alike the electromotive force and the resistance4 ,the electromotive force of the battery is the sum of the electromotive forces of all the cells1 and the resistance of the battery is the sum of the resistances of all the cells4 ,high electromotive forces or pressures capable of overcoming high resistances outside the battery can be obtained in this way4 ,figure #ad shows how the zincs are joined in parallel1 the zinc or negative pole of one being connected by wire to the zinc or negative pole of the rest1 and all the copper or positive poles together4 ,this arrangement does not increase the electromotive force1 but diminishes the resistance4 ,in fact1 the battery is equivalent to a single cell having plates equal in area to the total area of all the plates4 ,although unable to overcome a high resistance1 it can produce a large volume or quantity of electricity4 ,numerous voltaic combinations and varieties of cell have been found out4 ,in general1 where-ever two metals in contact are placed in a liquid which acts with more chemical energy on one than on the other1 as sulphuric acid does on zinc in preference to copper1 there is a development of electricity4 ,readers may have seen how an iron fence post corrodes at its junction with the lead that fixes it in the stone4 ,this decay is owing to the wet forming a voltaic couple with the two dissimilar metals and rusting the iron4 ,in the following list of materials1 when any two in contact are plunged in dilute acid1 that which is higher in the order becomes the positive plate or negative pole to that which is lower3-- ,,positive ,iron ,silver ,zinc ,nickel ,gold ,cadmium ,bismuth ,platinum ,tin ,antimony ,graphite ,lead ,copper ,,negative ,there being no chemical union between the hydrogen and copper in the zinc and copper couple1 that gas accumulates on the surface of the copper plate1 or is liberated in bubbles4 ,now1 hydrogen is positive compared with copper1 hence they tend to oppose each other in the combination4 ,the hydrogen diminishes the value of the copper1 the current grows weaker1 and the cell is said to polarise4 ,it follows that a simple water cell is not a good arrangement for the supply of a steady current4 ,the ,daniell cell is one of the best1 and gives a very constant current4 ,in this battery the copper plate is surrounded by a solution of sulphate of copper 7,cu ,,so#d71 which the hydrogen decomposes1 forming sulphuric acid 7,h#b,,so#d71 thus taking itself out of the way1 and leaving pure copper 7,cu7 to be deposited as a fresh surface on the copper plate4 ,a further improvement is made in the cell by surrounding the zinc plate with a solution of sulphate of zinc 7,zn ,,so#d71 which is a good conductor4 ,now1 when the oxide of zinc is formed by the oxygen uniting with the zinc1 the free sulphuric acid combines with it1 forming more sulphate of zinc1 and maintaining the ,,conductivity of the cell4 ,it is only necessary to keep up the supply of zinc1 water1 and sulphate of copper to procure a steady current of electricity4 ,the ,daniell cell is constructed in various ways4 ,in the earlier models the two plates with their solutions were separated by a porous jar or partition1 which allowed the solutions to meet without mixing1 and the current to pass4 ,sawdust moistened with the solutions is sometimes used for this porous separator1 for instance1 on board ships for laying submarine cables1 where the rolling of the waves would blend the liquids4 ,in the gravity ,daniell the solutions are kept apart by their specific gravities1 yet mingle by slow diffusion4 ,figure #ae illustrates this common type of cell1 where ,z is the zinc plate in a solution of sulphate of zinc1 and ,c is the copper plate in a solution of sulphate of copper1 fed by crystals of the blue vitriol4 ,the wires to connect the plates are shown at ,,ww4 ,it should be noticed that the zinc is cast like a wheel to expose a larger surface to oxidation1 and to reduce the resistance of the cell1 thus increasing the yield of current4 ,the extent of surface is not so important in the case of the copper plate1 which is not acted on1 and in this case is merely a spiral of wire1 helping to keep the solutions apart and the crystals down4 ,the ,daniell cell is much employed in telegraphy4 ,the ,bunsen cell consists of a zinc plate in sulphuric acid1 and at carbon plate in nitric acid1 with a porous separator between the liquids4 ,during the action of the cell1 hydrogen1 which is liberated at the carbon plate1 is removed by combining with the nitric acid4 ,the ,grove cell is a modification of the ,bunsen1 with platinum instead of carbon4 ,the ,smee cell is a zinc plate side by side with a platinised silver plate in dilute sulphuric acid4 ,the silver is coated with rough platinum to increase the surface and help to dislodge the hydrogen as bubbles and keep it from polarising the cell4 ,the ,bunsen1 ,grove1 and ,smee batteries are1 however1 more used in the laboratory than elsewhere4 ,the ,leclanche is a fairly constant cell1 which requires little attention4 ,it polarises in action but soon regains its normal strength when allowed to rest1 and hence it is useful for working electric bells and telephones4 ,as shown in figure #af1 it consists of a zinc rod with its connecting wire ,z1 and a carbon plate ,c with its binding screw1 between two cakes ,m ,m of a mixture of black oxide of manganese1 sulphur1 and carbon1 plunged in a solution of sal-ammoniac4 ,the oxide of manganese relieves the carbon plate of its hydrogen4 ,the strength of the solution is maintained by spare crystals of sal-ammoniac lying on the bottom of the cell1 which is closed to prevent evaporation1 but has a venthole for the escape of gas4 ,the ,bichromate of ,potash cell polarises more than the ,leclanche1 but yields a more powerful current for a short time4 ,it consists1 as shown in figure #ag1 of a zinc plate ,z between two carbon plates ,c ,c immersed in a solution of bichromate of potash1 sulphuric acid 7vitriol71 and water4 ,the zinc is always lifted out of the solution when the cell is not in use4 ,the gas which collects in the carbons1 and weakens the cell1 can be set free by raising the plates out of the liquid when the cell is not wanted4 ,stirring the solution has a similar effect1 and sometimes the constancy of the cell is maintained by a circulation of the liquid4 ,in ,fuller's bichromate cell the zinc is amalgamated with mercury1 which is kept in a pool beside it by means of a porous pot4 ,de la ,rue's chloride of silver cell 7fig4 #ah7 is1 from its constancy and small size1 well adapted for medical and testing purposes4 ,the plates are a little rod or pencil of zinc ,z1 and a strip or wire of silver ,s1 coated with chloride of silver and sheathed in parchment paper4 ,they are plunged in a solution of ammonium chloride ,a1 contained in a glass phial or beaker1 which is closed to suppress evaporation4 ,a tray form of the cell is also made by laying a sheet of silver foil on the bottom of the shallow jar1 and strewing it with dry chloride of silver1 on which is laid a jelly to support the zinc plate4 ,the jelly is prepared by mixing a solution of chloride of ammonium with agar-agar1 or ,ceylon moss4 ,this type permits the use of larger plates1 and adapts the battery for lighting small electric lamps4 ,skrivanoff has modified the ,de la ,rue cell by substituting a solution of caustic potash for the ammonium chloride1 and his battery has been used for star lights1 that is to say1 the tiny electric lamps of the ballet4 ,the ,schanschieff battery1 consisting of zinc and carbon plates in a solution of basic sulphate of mercury1 is suitable for reading1 mining1 and other portable lamps4 ,the ,latimer ,clark standard cell is used by electricians in testing1 as a constant electromotive force4 ,it consists of a pure zinc plate separated from a pool of mercury by a paste of mercurous proto-sulphate and saturated solution of sulphate of zinc4 ,platinum wires connect with the zinc and mercury and form the poles of the battery1 and the mouth of the glass cell is plugged with solid paraffin4 ,as it is apt to polarise1 the cell must not be employed to yield a current1 and otherwise much care should be taken of it4 ,dry cells are more cleanly and portable than wet1 they require little or no attention1 and are well suited for household or medical purposes4 ,the zinc plate forms the vessel containing the carbon plate and chemical reagents4 ,figure #ai represents a section of the ,e4 ,c4 ,c4 variety1 where ,z is the zinc standing on an insulating sole ,i1 and fitted with a connecting wire or terminal ,t 7-71 which is the negative pole4 ,the carbon ,c is embedded in black paste ,m1 chiefly composed of manganese dioxide1 and has a binding screw or terminal ,t 771 which is the positive pole4 ,the black paste is surrounded by a white paste ,z1 consisting mainly of lime and sal-ammoniac4 ,there is a layer of silicate cotton ,s ,c above the paste1 and the mouth is sealed with black pitch ,p1 through which a waste-tube ,w ,t allows the gas to escape4 ,the ,hellesen dry cell is like the ,e4 ,c4 ,c41 but contains a hollow carbon1 and is packed with sawdust in a millboard case4 ,the ,leclanche-,barbier dry cell is a modification of the ,leclanche wet cell1 having a paste of sal-ammoniac instead of a solution4 ,all the foregoing cells are called primary1 because they are generators of electricity4 ,there are1 however1 batteries known as secondary1 which store the current as the ,leyden jar stores up the discharge from an electrical machine4 ,in the action of a primary cell1 as we have seen1 water is split into its constituent gases1 oxygen and hydrogen4 ,moreover1 it was discovered by ,carlisle and ,nicholson in the year #ahjj that the current of a battery could decompose water in the outer part of the circuit4 ,their experiment is usually performed by the4 apparatus shown in figure #bj1 which is termed a voltameter1 and consists of a glass vessel ,v1 containing water acidulated with a little sulphuric acid to render it a better conductor1 and two glass test-tubes ,,oh inverted over two platinum strips or electrodes1 which rise up from the bottom of the vessel and are connected underneath it to wires from the positive and negative poles of the battery ,c ,z4 ,it will be understood that the current enters the water by the positive electrode1 and leaves it by the negative electrode4 ,when the power of the battery is sufficient the water in the vessel is decomposed1 and oxygen being the negative element1 collects at the positive foil or electrode1 which is covered by the tube ,o4 ,the hydrogen1 on the other hand1 being positive1 collects at the negative foil under the tube ,h4 ,these facts can be proved by dipping a red-hot wick or taper into the gas of the tube ,o and seeing it blaze in presence of the oxygen which feeds the combustion1 then dipping the lighted taper into the gas of the tube ,h and watching it burn with the blue flame of hydrogen4 ,the volume of gas at the ,,cathode or negative electrode is always twice that at the ,,anode or positive electrode1 as it should be according to the known composition of water4 ,now1 if we disconnect the battery and join the two platinum electrodes of the voltameter by a wire1 we shall find a current flowing out of the voltameter as though it were a battery1 but in the reverse direction to the original current which decomposed the water4 ,this secondary or reacting current is evidently due to the polarisation of the foils--that is to say1 the electro- positive and electro-negative gases collected on them4 ,professor ,groves constructed a gas battery on this principle1 the plates being of platinum and the two gases surrounding them oxygen and hydrogen1 but the most useful development of it is the accumulator or storage battery4 ,the first practicable secondary battery of ,gaston ,plante was made of sheet lead plates or electrodes1 kept apart by linen cloth soaked in dilute sulphuric acid1 after the manner of ,volta's pile4 ,it was charged by connecting the plates to a primary battery1 and peroxide of lead 7,pb,o#b7 was formed on one plate and spongy lead 7,pb7 on the other4 ,when the charging current was cut off the peroxide plate became the positive and the spongy plate the negative pole of the secondary cell4 ,faure improved the ,plante cell by adding a paste of red lead or minium 7,pb#bjd7 and dilute sulphuric acid 7,h#b,,so#d71 by which a large quantity of peroxide and spongy lead could be formed on the plates4 ,sellon and ,volckmar increased its efficiency by putting the paste into holes cast in the lead4 ,the ,e4 ,p4 ,s4 accumulator of the ,electrical ,power ,storage ,company is illustrated in figure #ba1 and consists of a glass or teak box containing two sets of leaden grids perforated with holes1 which are primed with the paste and steeped in dilute sulphuric acid4 ,alternate grids are joined to the poles of a charging battery or generator1 those connected to the positive pole being converted into peroxide of lead and the others into spongy lead4 ,the terminal of the peroxide plates1 being the positive pole of the accumulator1 is painted red1 and that of the spongy plates or negative pole black4 ,accumulators of this kind are highly useful as reservoirs of electricity for maintaining the electric light1 or working electric motors in tramcars1 boats1 and other carriages4 ,,chapter ,,iii4 ,,the ,,electricity ,,of ,,heat4 ,in the year #ahba ,professor ,seebeck1 of ,berlin1 discovered a third source of electricity4 ,volta had found that two dissimilar metals in contact will produce a current by chemical action1 and ,seebeck showed that heat might take the place of chemical action4 ,thus1 if a bar of antimony ,a 7fig4 #bb7 and a bar of bismuth ,s are in contact at one end1 and the junction is heated by a spirit lamp to a higher temperature than the rest of the bars1 a difference in their electric state or potential will be set up1 and if the other ends are joined by a wire ,w1 a current will flow through the wire4 ,the direction of the current1 indicated by the arrow1 is from the bismuth to the antimony across the joint1 and from the antimony to the bismuth through the external wire4 ,this combination1 which is called a thermo-electric couple1 is clearly analogous to the voltaic couple1 with heat in place of chemical affinity4 ,the direction of the current within and without the couple shows that the bismuth is positive to the antimony4 ,this property of generating a current of electricity by contact under the influence of heat is not confined to bismuth and antimony1 or even to the metals1 but is common to all dissimilar substances in their degree4 ,in the following list of bodies each is positive to those beneath it1 negative to those above it1 and the further apart any two are in the scale the greater the effect4 ,thus bismuth and antimony give a much stronger current with the same heating than copper and iron4 ,bismuth and selenium produce the best result1 but selenium is expensive and not easy to manipulate4 ,copper and ,german silver will make a cheap experimental couple3-- ,,positive ,bismuth ,cobalt ,potassium ,nickel ,sodium ,lead ,tin ,copper ,platinum ,silver ,zinc ,cadmium ,arsenic ,iron ,red phosphorus ,antimony ,tellurium ,selenium ,,negative ,other things being equal1 the hotter the joint in comparison with the free ends of the bars the stronger the current of electricity4 ,within certain limits the current is1 in fact1 proportional to this difference of temperature4 ,it always flows in the same direction if the joint is not overheated1 or1 in other words1 raised above a certain temperature4 ,the electromotive force and current of a thermo-electric couple is very much smaller than that given by an ordinary voltaic cell4 ,we can1 however1 multiply the effect by connecting a number of pairs together1 and so forming a pile or battery4 ,thus figure #bc shows three couples joined in series1 the positive pole of one being connected to the negative pole of the next4 ,now1 if all the junctions on the left are hot and those on the right are cool1 we will get the united effect of the whole1 and the total current will flow through the wire ,w1 joining the extreme bars or positive and negative poles of the battery4 ,it must be borne in mind that although the bismuth and antimony of this thermo-electric battery1 like the zinc and copper of the voltaic or chemico-electric battery1 are respectively positive and negative to each other1 the poles or wires attached to these metals are1 on the contrary1 negative and positive4 ,this peculiarity arises from the current starting between the bismuth and antimony at the heated junction4 ,the internal resistance of a thermo-electric pile is1 of course1 very slight1 the metals being good conductors1 and this fact gives it a certain advantage over the voltaic battery4 ,moreover1 it is cleaner and less troublesome than the chemical battery1 for it is only necessary to keep at the required difference of temperature between the hot and cold junctions in order to get a steady current4 ,no solutions or salts are required1 and there appears to be little or no waste of the metals4 ,it is important1 however1 to avoid sudden heating and cooling of the joints1 as this tends to destroy them4 ,clammond1 ,gulcher1 and others have constructed useful thermo-piles for practical purposes4 ,figure #bd illustrates a ,clammond thermo- pile of #ge couples or elements4 ,the metals forming these pairs are an alloy of bismuth and antimony for one and iron for the other4 ,prisms of the alloy are cast on strips of iron to form the junctions4 ,they are bent in rings1 the junctions in a series making a zig-zag round the circle4 ,the rings are built one over the other in a cylinder of couples1 and the inner junctions are heated by a ,bunsen gas-burner in the hollow core of the battery4 ,a gas- pipe seen in front leads to the burner1 and the wires ,,ww connected to the extreme bars or poles are the electrodes of the pile4 ,thermo-piles are interesting from a scientific point of view as a direct means of transforming heat into electricity4 ,a sensitive pile is also a delicate detector of heat by virtue of the current set up1 which can be measured with a galvanometer or current meter4 ,piles of antimony and bismuth are made which can indicate the heat of a lighted match at a distance of several yards1 and even the radiation from certain of the stars4 ,thermo-batteries have been used in ,france for working telegraphs1 and they are capable of supplying small installations of the electric light or electric motors for domestic purposes4 ,the action of the thermo-pile1 like that of a voltaic cell1 can be reversed4 ,by sending a current through the couple from the antimony to the bismuth we shall find the junction cooled4 ,this ,peltier effect1 as it is termed1 after its discoverer1 has been known to freeze water1 but no practical application has been made of it4 ,a very feeble thermo-electric effect can be produced by heating the junction of two different pieces of the same substance1 or even by making one part of the same conductor hotter than another4 ,thus a sensitive galvanometer will show a weak current if a copper wire connected in circuit with it be warmed at one point4 ,moreover1 it has been found by ,lord ,kelvin that if an iron wire is heated at any point1 and an electric current be passed through it1 the hot point will shift along the wire in a direction contrary to that of the current4 ,,chapter ,,iv4 ,,the ,,electricity ,,of ,,magnetism4 ,we have already seen how electricity was first produced by the simple method of rubbing one body on another1 then by the less obvious means of chemical union1 and next by the finer agency of heat4 ,in all these1 it will be observed1 a substantial contact is necessary4 ,we have now to consider a still more subtle process of generation1 not requiring actual contact1 which1 as might be expected1 was discovered later1 that1 mainly through the medium of magnetism4 ,the curious mineral which has the property of attracting iron was known to the ,chinese several thousand years ago1 and certainly to the ,greeks in the times of ,thales1 who1 as in the case of the rubbed amber1 ascribed the property to its possession of a soul4 ,lodestone1 a magnetic oxide of iron 7,,fe#c,o#d71 is found in various parts of ,china1 especially at ,t'szchou in ,southern ,chihli1 which was formerly known as the ,city of the ,magnet4 ,it was called by the ,chinese the love-stone or thsu-chy1 and the stone that snatches iron or ny-thy-chy1 and perchance its property of pointing out the north and south direction was discovered by dropping a light piece of the stone1 if not a sewing needle made of it1 on the surface of still water4 ,at all events1 we read in ,pere ,du ,halde's ,description de la ,chine1 that sometime in or about the year #bfce ,b4,c4 the great ,emperor ,hoang-ti1 having lost his way in a fog whilst pursuing the rebellious ,prince ,tchiyeou on the plains of ,tchou-lou1 constructed a chariot which showed the cardinal points1 thus enabling him to overtake and put the prince to death4 ,a magnetic car preceded the ,emperors of ,china in ceremonies of state during the fourth century of our era4 ,it contained a genius in a feather dress who pointed to the south1 and was doubtless moved by a magnet floating in water or turning on a pivot4 ,this rude appliance was afterwards refined into the needle compass for guiding mariners on the sea1 and assisting the professors of feng- shui or geomancy in their magic rites4 ,magnetite was also found at ,heraclea in ,lydia1 and at ,magnesium on the ,meander or ,magnesium at ,sipylos1 all in ,asia ,minor4 ,it was called the ,heraclean ,stone by the people1 but came at length to bear the name of ,magnet after the city of ,magnesia or the mythical shepherd ,magnes1 who was said to have discovered it by the attraction of his iron crook4 ,the ancients knew that it had the power of communicating its attractive property to iron1 for we read in ,plato's ,ion that a number of iron rings can be supported in a chain by the ,heraclean ,stone4 ,lucretius also describes an experiment in which iron filings are made to rise up and rave in a brass basin by a magnet held underneath4 ,we are told by other writers that images of the gods and goddesses were suspended in the air by lodestone in the ceilings of the temples of ,diana of ,ephesus1 of ,serapis at ,alexandria1 and others4 ,it is surprising1 however1 that neither the ,greeks nor ,romans1 with all their philosophy1 would seem to have discovered its directive property4 ,during the dark ages pieces of ,lodestone mounted as magnets were employed in the black arts4 ,a small natural magnet of this kind is shown in figure #be1 where ,l is the stone shod with two iron pole-pieces1 which are joined by a keeper ,a or separable bridge of iron carrying a hook for supporting weights4 ,apparently it was not until the twelfth century that the compass found its way into ,europe from the ,east4 ,in the ,landnammabok of ,ari ,frode1 the ,norse historian1 we read that ,flocke ,vildergersen1 a renowned viking1 sailed from ,norway to discover ,iceland in the year #hfh1 and took with him two ravens as guides1 for in those days the seamen had no lodestone 7that is1 no lidar stein1 or leading stone7 in the northern countries4 ,the ,bible1 a poem of ,guiot de ,provins1 minstrel at the court of ,barbarossa1 which was written in or about the year #hij1 contains the first mention of the magnet in the ,west4 ,guiot relates how mariners have an art which cannot deceive of finding the position of the polestar1 that does not move4 ,after touching a needle with the magnet1 an ugly brown stone which draws iron to itself1 he says they put the needle on a straw and float it on water so that its point turns to the hidden star1 and enables them to keep their course4 ,arab traders had probably borrowed the floating needle from the ,chinese1 for ,bailak ,kibdjaki1 author of the ,merchant's ,treasure1 written in the thirteenth century1 speaks of its use in the ,syrian sea4 ,the first ,crusaders were probably instrumental in bringing it to ,france1 at all events ,jacobus de ,vitry 7#abjd-ae7 and ,vincent de ,beauvais 7#abej7 mention its use1 ,de ,beauvais calling the poles of the needle by the ,arab words aphron and zohran4 ,ere long the needle was mounted on a pivot and provided with a moving card showing the principal directions4 ,the variation of the needle from the true north and south was certainly known in ,china during the twelfth1 and in ,europe during the thirteenth century4 ,columbus also found that the variation changed its value as he sailed towards ,america on his memorable voyage of #adib4 ,moreover1 in #aegf1 ,norman1 a compass maker in ,london1 showed that the north- seeking end of the needle dipped below the horizontal4 ,in these early days it was supposed that lodestone in the pole- star1 that is to say1 the lodestar of the poets or in mountains of the far north1 attracted the trembling needle2 but in the year #afjj1 ,dr4 ,gilbert1 the founder of electric science1 demonstrated beyond a doubt that the whole earth was a great magnet4 ,a magnet1 as is well known1 has1 like an electric battery1 always two poles or centres of attraction1 which are situated near its extremities4 ,sometimes1 indeed1 when the magnet is imperfect1 there are consequent poles of weaker force between them4 ,one of the poles is called the north1 and the other the south1 because if the magnet were freely pivotted like a compass needle1 the former would turn to the north and the latter to the south4 ,either pole will attract iron1 but soft or annealed iron does not retain the magnetism nearly so well as steel4 ,hence a boy's test for the steel of his knife is only efficacious when the blade itself becomes magnetic after being touched with the magnet4 ,a piece of steel is readily magnetised by stroking it from end to end in one direction with the pole of a magnet1 and in this way compass needles and powerful bar magnets can be made4 ,the poles attract iron at a distance by induction1 just as a charge of electricity1 be it positive or negative1 will attract a neutral pith ball2 and ,dr4 ,gilbert showed that a north pole always repels another north pole and attracts a south pole1 while1 on the other hand1 a south pole always repels a south pole and attracts a north pole4 ,this can be proved by suspending a magnetic needle like a pithball1 and approaching another towards it1 as illustrated in figure #bf1 where the north pole ,n attracts the south ,s4 ,obviously there are two opposite kinds of magnetic poles1 as of electricity1 which always appear together1 and like magnetic poles repel1 unlike magnetic poles attract each other4 ,it follows that the magnetic pole of the compass needle which turns to the north must be unlike the north and like the south magnetic pole of the earth4 ,instead of calling it the north1 it would be less confusing to call it the north-seeking pole of the needle4 ,gilbert made a terella1 or miniature of the earth1 as a magnet1 and not only demonstrated how the compass needle sets along the lines joining the north and south magnetic poles1 but explained the variation and the dip4 ,he imagined that the magnetic poles coincided with the geographical poles1 but1 as a matter of fact1 they do not1 and1 moreover1 they are slowly moving round the geographical poles1 hence the declination of the needle1 that is to say its angle of divergence from the true meridian or north and south line1 is gradually changing4 ,the north magnetic pole of the earth was actually discovered by ,sir ,john ,ross north of ,british ,america1 on the coast of ,boothia 7latitude #gj degrees #e' ,n1 longitude #if degrees #df' ,w71 where1 as foreseen1 the needle entirely lost its directive property and stood upright1 or1 so to speak1 on its head4 ,the south magnetic pole lies in the ,prince ,albert range of ,victona ,land1 and was almost reached by ,sir ,james ,clark ,ross4 ,the magnetism of the earth is such as might be produced by a powerful magnet inside1 but its origin is unknown1 although there is reason to believe that masses of lodestone or magnetic iron exist in the crust4 ,coulomb found that not only iron1 but all substances are more or less magnetic1 and ,faraday showed in #ahde that while some are attracted by a magnet others are repelled4 ,the former he called paramagnetic and the latter diamagnetic bodies4 ,the following is a list of these4-- ,paramagnetic ,diamagnetic ,iron ,bismuth ,nickel ,phosphorus ,cobalt ,antimony ,aluminium ,zinc ,manganese ,mercury ,chromium ,lead ,cerium ,silver ,titanium ,copper ,platinum ,water ,many ores and ,alcohol salts of the ,tellurium above metals ,selenium ,oxygen ,sulphur ,thallium ,hydrogen ,air ,we have theories of magnetism that reduce it to a phenomenon of electricity1 though we are ignorant of the real nature of both4 ,if we take a thin bar magnet and break it in two1 we find that we have now two shorter magnets1 each with its north and south poles1 that is to say1 poles of the same kind as the south and north--magnetic poles of the earth4 ,if we break each of these again1 we get four smaller magnets1 and we can repeat the process as often as we like4 ,it is supposed1 therefore1 that every atom of the bar is a little magnet in itself having its two opposite poles1 and that in magnetising the bar we have merely partially turned all these atoms in one direction1 that is to say1 with their north poles pointing one way and their south poles the other way1 as shown in figure #bg4 ,the polarity of the bar only shows itself at the ends1 where the molecular poles are1 so to speak1 free4 ,there are many experiments which support this view4 ,for example1 if we heat a magnet red hot it loses its magnetism1 perhaps because the heat has disarranged the particles and set the molecular poles in all directions4 ,again1 if we magnetise a piece of soft iron we can destroy its magnetism by striking it so as to agitate its atoms and throw them out of line4 ,in steel1 which is iron with a small admixture of carbon1 the atoms are not so free as in soft iron1 and hence1 while iron easily loses its magnetism1 steel retains it1 even under a shock1 but not under a cherry red- heat4 ,nevertheless1 if we put the atoms of soft iron under a strain by bending it1 we shall find it retain its magnetism more like a bit of steel4 ,it has been found1 too1 that the atoms show an indisposition to be moved by the magnetising force which is known as ,,hysteresis4 ,they have a certain inertia1 which can be overcome by a slight shock1 as though they had a difficulty of turning in the ranks to take up their new positions4 ,even if this molecular theory is true1 however1 it does not help us to explain why a molecule of matter is a tiny magnet4 ,we have only pushed the mystery back to the atom4 ,something more is wanted1 and electricians look for it in the constitution of the atom1 and in the luminiferous ether which is believed to surround the atoms of matter1 and to propagate not merely the waves of light1 but induction from one electrified body to another4 ,we know in proof of this ethereal action that the space around a magnet is magnetic4 ,thus1 if we lay a horse-shoe magnet on a table and sprinkle iron filings round it1 they will arrange themselves in curving lines between the poles1 as shown in figure #bh4 ,each filing has become a little magnet1 and these set themselves end to end as the molecules in the metal are supposed to do4 ,the field about the magnet is replete with these lines1 which follow certain curves depending on the arrangement of the poles4 ,in the horse- shoe magnet1 as seen1 they chiefly issue from one pole and sweep round to the other4 ,they are never broken1 and apparently they are lines of stress in the circumambient ether4 ,a pivoted magnet tends to range itself along these lines1 and thus the compass guides the sailor on the ocean by keeping itself in the line between the north and south magnetic poles of the earth4 ,faraday called them lines of magnetic force1 and said that the stronger the magnet the more of these lines pass through a given space4 ,along them magnetic induction is supposed to be propagated1 and a magnet is thus enabled to attract iron or any other magnetic substance4 ,the pole induces an opposite pole to itself in the nearest part of the induced body and a like pole in the remote part4 ,consequently1 as unlike poles attract and like repel1 the soft iron is attracted by the inducing pole much as a pithball is attracted by an electric charge4 ,the resemblances of electricity and magnetism did not escape attention1 and the derangement of the compass needle by the lightning flash1 formerly so disastrous at sea1 pointed to an intimate connection between them1 which was ultimately disclosed by ,professor ,oersted1 of ,copenhagen1 in the year #ahbj4 ,oersted was on the outlook for the required clue1 and a happy chance is said to have rewarded him4 ,his experiment is shown in figure #bi1 where a wire conveying a current of electricity flowing in the direction of the arrow is held over a pivoted magnetic needle so that the current flows from south to north4 ,the needle will tend to set itself at right angles to the wire1 its north or north-seeking pole moving towards the west4 ,if the direction of the current is reversed1 the needle is deflected in the opposite direction1 its north pole moving towards the east4 ,further1 if the wire is held below the needle1 in the first place1 the north pole will turn towards the east1 and if the current be reversed it will move towards the west4 ,the direction of a current can thus be told with the aid of a compass needle4 ,when the wire is wound many times round the needle on a bobbin1 the whole forms what is called a galvanoscope1 as shown in figure #cj1 where ,n is the needle and ,b the bobbin4 ,when a proper scale is added to the needle by which its deflections can be accurately read1 the instrument becomes a current measurer or galvanometer1 for within certain limits the deflection of the needle is proportional to the strength of the current in the wire4 ,a rule commonly given for remembering the movement of the needle is as follows3--,imagine yourself laid along the wire so that the current flows from your feet to your head2 then if you face the needle you will see its north pole go to the left and its south pole to the right4 ,i find it simpler to recollect that if the current flows from your head to your feet a north pole will move round you from left to right in front4 ,or1 again1 if a current flows from north to south1 a north pole will move round it like the sun round the earth4 ,the influence of the current on the needle implies a magnetic action1 and if we dust iron filings around the wire we shall find they cling to it in concentric layers1 showing that circular lines of magnetic force enclose it like the water waves caused by a stone dropped into a pond4 ,figure #ca represents the section of a wire carrying a current1 with the iron filings arranged in circles round it4 ,since a magnetic pole tends to move in the direction of the lines of force1 we now see why a north or south pole tends to move ,,round a current1 and why a compass needle tries to set itself at right angles to a current1 as in the original experiment of ,oersted4 ,the needle1 having two opposite poles1 is pulled in opposite directions by the lines1 and being pivoted1 sets itself tangentically to them4 ,were it free and flexible1 it would curve itself along one of the lines4 ,did it consist of a single pole1 it would revolve round the wire4 ,action and re-action are equal and opposite1 hence if the needle is fixed and the wire free the current will move round the magnet2 and if both are free they will circle round each other4 ,applying the above rule we shall find that when the north pole moves from left to right the current moves from right to left4 ,ampere of ,paris1 following ,oersted1 promptly showed that two parallel wires carrying currents attracted each other when the currents flowed in the same direction1 and repelled each other when they flowed in opposite directions4 ,thus1 in figure #cb1 if ,a and ,b are the two parallel wires1 and ,a is mounted on pivots and free to move in liquid contacts of mercury1 it will be attracted or repelled by ,b according as the two currents flow in the same or in opposite directions4 ,if the wires cross each other at right angles there is no attraction or repulsion4 ,if they cross at an acute angle1 they will tend to become parallel like two compass needles1 when the currents are in one direction1 and to open to a right angle and close up the other way when the currents are in opposite directions1 always tending to arrange themselves parallel and flowing in the same direction4 ,these effects arise from the circular lines of force around the wire4 ,when the currents are similar the lines act as unlike magnetic poles and attract1 but when the currents are dissimilar the lines act as like magnetic poles and repel each other4 ,another important discovery of ,ampere is that a circular current behaves like a magnet2 and it has been suggested by him that the atoms are magnets because each has a circular current flowing round it4 ,a series of circular currents1 such as the spiral ,s in figure #cc gives1 when connected to a battery ,c ,z1 is in fact a skeleton ,,electro-,,magnet having its north and south poles at the extremities4 ,if a rod or core of soft iron ,i be suspended by fibres from a support1 it will be sucked towards the middle of the coil as into a vortex1 by the circular magnetic lines of every spire or turn of the coil4 ,such a combination is sometimes called a solenoid1 and is useful in practice4 ,when the core gains the interior of the coil it becomes a veritable electromagnet1 as found by ,arago1 having a north pole at one end and a south pole at the other4 ,figure #cd illustrates a common poker magnetised in the same way1 and supporting nails at both ends4 ,the poker has become the core of the electromagnet4 ,on reversing the direction of the current through the spiral we reverse the poles of the core1 for the poker being of soft or wrought iron1 does not retain its magnetism like steel4 ,if we stop the current altogether it ceases to be a magnet1 and the nails will drop away from it4 ,ampere's experiment in figure #cb has shown us that two currents1 more or less parallel1 influence each other2 but in #ahca ,professor ,faraday of the ,royal ,institution1 ,london1 also found that when a current is started and stopped in a wire1 it induces a momentary and opposite current in a parallel wire4 ,thus1 if a current is ,,started in the wire ,b 7fig4 #cb7 in direction of the arrow1 it will induce or give rise to a momentary current in the wire ,a1 flowing in a contrary direction to itself4 ,again1 if the current in ,b be ,,stopeed1 a momentary current is set up in the wire ,a in a direction the same as that of the exciting current in ,b4 ,while the current in ,b is quietly flowing there is no induced current in ,a2 and it is only at the start or the stoppage of the inducing or ,,primary current that the induced or ,,secondary current is set up4 ,here again we have the influence of the magnetic field around the wire conveying a current4 ,this is the principle of the induction coil so much employed in medical electricity1 and of the transformer or converter used in electric illumination4 ,it consists essentially1 as shown in figure #ce1 of two coils of wire1 one enclosing the other1 and both parallel or concentric4 ,the inner or primary coil ,p ,c is of short thick wire of low resistance1 and is traversed by the inducing current of a battery ,b4 ,to increase its inductive effect a core of soft iron ,i ,c occupies its middle4 ,the outer or secondary coil ,s ,c is of long thin wire terminating in two discharging points ,d#a ,d#b4 ,an interrupter or hammer key interrupts or makes and breaks the circuit of the primary coil very rapidly1 so as to excite a great many induced currents in the secondary coil per second1 and produce energetic sparks between the terminals ,d#a ,d#b4 ,the interrupter is actuated automatically by the magnetism of the iron core ,i ,c1 for the hammer ,h has a soft iron head which is attracted by the core when the latter is magnetised1 and being thus drawn away from the contact screw ,c ,s the circuit of the primary is broken1 and the current is stopped4 ,the iron core then ceases to be a magnet1 the hammer ,h springs back to the contact screw1 and the current again flows in the primary circuit only to be interrupted again as before4 ,in this way the current in the primary coil is rapidly started and stopped many times a second1 and this1 as we know1 induces corresponding currents in the secondary which appear as sparks at the discharging points4 ,the effect of the apparatus is enhanced by interpolating a condenser ,c ,c in the primary circuit4 ,a condenser is a form of ,leyden jar1 suitable for current electricity1 and consists of layers of tinfoil separated from each other by sheets of paraffin paper1 mica1 or some other convenient insulator1 and alternate foils are connected together4 ,the wires joining each set of plates are the poles of the condenser1 and when these are connected in the circuit of a current the condenser is charged4 ,it can be discharged by joining its two poles with a wire1 and letting the two opposite electricities on its plates rush together4 ,now1 the sudden discharge of the condenser ,c ,c through the primary coil ,p ,c enhances the inductive effect of the current4 ,the battery ,b1 here shown by the conventional symbol ,electrical ,symbol where the thick dash is the negative and the thin dash the positive pole1 is connected between the terminals ,t#a ,t#b1 and a ,,commutator or pole- changer ,r1 turned with a handle1 permits the direction of the current to be reversed at will4 ,figure #cf represents the exterior of an ordinary induction coil of the ,ruhmkorff pattern1 with its two coils1 one over the other ,c1 its commutator ,r1 and its sparkling points ,d#a;,d#b1 the whole being mounted on a mahogany base1 which holds the condenser4 ,the intermittent1 or rather alternating1 currents from the secondary coil are often applied to the body in certain nervous disorders4 ,when sent through glass tubes filled with rarefied gases1 sometimes called ,geissler tubes1 they elicit glows of many colours1 vieing in beauty with the fleeting tints of the aurora polaris1 which1 indeed1 is probably a similar effect of electrical discharges in the atmosphere4 ,the action of the induction is reversible4 ,we can not only send a current of low pressure from a generator of weak electromotive force through the primary coil1 and thus excite a current of high pressure in the secondary coil1 but we can send a current of high pressure through the secondary coil and provoke a current of low pressure in the primary coil ,the transformer or converter1 a modified induction coil used in distributing electricity to electric lamps and motors1 can not only transform a low pressure current into a high1 but a high pressure current into a low4 ,as the high pressure currents are best able to overcome the resistance of the wire convening them1 it is customary to transmit high pressure currents from the generator to the distant place where they are wanted by means of small wires1 and there transform them into currents of the pressure required to light the lamps or drive the motors4 ,we come now to another consequence of ,oersted's great discovery1 which is doubtless the most important of all1 namely1 the generation of electricity from magnetism1 or1 as it is usually called1 magneto-electric induction4 ,in the year #ahca the illustrious ,michael ,faraday further succeeded in demonstrating that when a magnet ,m is thrust into a hollow coil of wire ,c1 as shown in figure #cg1 a current of electricity is set up in the coil whilst the motion lasts4 ,when the magnet is withdrawn again another current is induced in the reverse direction to the first4 ,if the coil be closed through a small galvanometer ,g the movements of the needle to one side or the other will indicate these temporary currents4 ,it follows from the principle of action and reaction that if the magnet is kept still and the coil thrust over it similar currents will be induced in the coil4 ,all that is necessary is for the wires to cut the lines of magnetic force around the magnet1 or1 in other words1 the lines of force in a magnetic field ,we have seen already that a wire conveying a current can move a magnetic pole1 and we are therefore prepared to find that a magnetic pole moved near a wire can excite a current in it4 ,figure #ch illustrates the conditions of this remarkable effect1 where ,n and ,s are two magnetic poles with lines of force between them1 and ,w is a wire crossing these lines at right angles1 which is the best position4 ,if1 now1 this wire be moved so as to sink bodily through the paper away from the reader1 an electric current flowing in the direction of the arrow will be induced in it4 ,if1 on the contrary1 the wire be moved across the lines of force towards the reader1 the induced current will flow oppositely to the arrow4 ,moreover1 if the poles of the magnet ,n and ,s exchange places1 the directions of the induced currents will also be reversed4 ,this is the fundamental principle of the well known dynamo-electric machine1 popularly called a dynamo4 ,again1 if we send a current from some external source through the wire in the direction of the arrow1 the wire will move ,,of ,,itself across the lines of force away from the reader1 that is to say1 in the direction it would need to be moved in order to excite such a current2 and if1 on the other hand1 the current be sent through it in the reverse direction to the arrow1 it will move towards the reader4 ,this is the principle of the equally well-known electric motor4 ,figure #ci shows a simple method of remembering these directions4 ,let the right hand rest on the north pole of a magnet and the forefinger be extended in the direction of the lines of force1 then the outstretched thumb will indicate the direction in which the wire or conductor moves and the bent middle finger the direction of the current4 ,these three digits1 as will be noticed1 are all at right angles to each other1 and this relation is the best for inducing the strongest current in a dynamo or the most energetic movement of the conductor in an electric motor4 ,of course in a dynamo-electric generator the stronger the magnetic field1 the less the resistance of the conductor1 and the faster it is moved across the lines of force1 that is to say1 the more lines it cuts in a second the stronger is the current produced4 ,similarly in an electric motor1 the stronger the current and magnetic field the faster will the conductor move4 ,the most convenient motion to give the conductor in practice is one of rotation1 and hence the dynamo usually consists of a coil or series of coils of insulated wire termed the armature1 which is mounted on a spindle and rapidly rotated in a strong magnetic field between the poles of powerful magnets4 ,currents are generated in the coils1 now in one direction then in another1 as they revolve or cross different parts of the field2 and1 by means of a device termed a commutator1 these currents can be collected or sifted at will1 and led away by wires to an electric lamp1 an accumulator1 or an electric motor1 as desired4 ,the character of the electricity is precisely the same as that generated in the voltaic battery4 ,the commutator may only collect the currents as they are generated1 and supply what is called an alternating current1 that is to say1 a current which alternates or changes its direction several hundred times a second1 or it may sift the currents as they are produced and supply what is termed a continuous current1 that is1 a current always in the same direction1 like that of a voltaic battery4 ,some machines are made to supply alternating currents1 others continuous currents4 ,either class of current will do for electric lamps1 but only continuous currents are used for electo-plating1 or1 in general1 for electric motors4 ,in the magneto-electric machine the ,,field ,,magnets are simply steel bars permanently magnetised1 but in the ordinary dynamo the field magnets are electro-magnets excited to a high pitch by means of the current generated in the moving conductor or armature4 ,in the series-wound machine the whole of the current generated in the armature also goes through the coils of the field magnets4 ,such a machine is sketched in figure #dj1 where ,a is the armature1 consisting of an iron core surrounded by coils of wire and rotating in the field of a powerful electro-magnet ,,ns in the direction of the arrows4 ,for the sake of simplicity only twelve coils are represented4 ,they are all in circuit one with another1 and a wire connects the ends of each coil to corresponding metal bars on the commutator ,c4 ,these bars are insulated from each other on the spindle ,x of the armature4 ,now1 as each coil passes through the magnetic field in turn1 a current is excited in it4 ,each coil therefore resembles an individual cell of a voltaic battery1 connected in series4 ,the current is drawn off from the ring by two copper brushes b1 be which rub upon the bars of the commutator at opposite ends of a diameter1 as shown4 ,one brush is the positive pole of the dynamo1 the other is the negative1 and the current will flow through any wire or external circuit which may be connected with these1 whether electric lamps1 motors1 accumulators1 electro-plating baths1 or other device4 ,the small arrows show the movements of the current throughout the machine1 and the terminals are marked 77 positive and 7-7 negative4 ,it will be observed that the current excited in the armature also flows through the coils of the electro-magnets1 and thus keeps up their strength4 ,when the machine is first started the current is feeble1 because the field of the magnets in which the armature revolves is merely that due to the dregs or residual magnetism left in the soft iron cores of the magnet since the last time the machine was used4 ,but this feeble current exalts the strength of the field-magnets1 producing a stronger field1 which in turn excites a still stronger current in the armature1 and this process of give and take goes on until the full strength or saturation of the magnets is attained4 ,such is the series dynamo1 of which the well-known ,gramme machine is a type4 ,figure #da illustrates this machine as it is actually made1 ,a being the armature revolving between the poles ,,ns of the field-magnets ,m1 ,m1 ,m' ,m'1 on a spindle which is driven by means of a belt on the pulley ,p from a separate engine ,the brushes b b' of the commutator ,c collect the current1 which in this case is continuous1 or constant in its direction4 ,the current of the series machine varies with the resistance of the external or working circuit1 because that is included in the circuit of the field magnets and the armature4 ,thus1 if we vary the number of electric lamps fed by the machine1 we shall vary the current it is capable of yielding4 ,with arc lamps in series1 by adding to the number in circuit we increase the resistance of the outer circuit1 and therefore diminish the strength of the current yielded by the machine1 because the current1 weakened by the increase of resistance1 fails to excite the field magnets as strongly as before4 ,on the other hand1 with glow lamps arranged in parallel1 the reverse is the case1 and putting more lamps in circuit increases the power of the machine1 by diminishing the resistance of the outer circuit in providing more cross-cuts for the current4 ,this1 of course1 is a drawback to the series machine in places where the number of lamps to be lighted varies from time to time4 ,in the shunt-wound machine the field magnets are excited by diverting a small portion of the main current from the armature through them1 by means of a shunt or loop circuit4 ,thus in figure #db where ,c is the commutator and b b' the brushes1 ,m is a shunt circuit through the magnets1 and ,e is the external or working circuit of the machine4 ,the small arrows indicate the directions of the currents4 ,with this arrangement the addition of more glow lamps to the external circuit ,e ,,diminishes the current1 because the portion of it which flows through the by-path ,m1 and excites the magnets1 is less now that the alternative route for the current through ,e is of lower resistance than before4 ,when fewer glow lamps are in the external circuit ,e1 and its resistance therefore higher1 the current in the shunt circuit ,m is greater than before1 the magnets become stronger1 and the electromotive force of the armature is increased4 ,the ,edison machine is of this type1 and is illustrated in figure #dc1 where ,m ,m' are the field magnets with their poles ,n ,s1 between which the armature ,a is revolved by means of the belt ,b1 and a pulley seen behind4 ,the leading wires ,w ,w convey the current from the brushes of the commutator to the external circuit4 ,in this machine the conductors of the armature are not coils of wire1 but separate bars of copper4 ,in shunt machines the variation of current due to a varying number of lamps in use occasions a rise and fall in the brightness of the lamps which is undesirable1 and hence a third class of dynamo has been devised1 which combines the principles of both the series and shunt machines4 ,this is the compound-wound machine1 in which the magnets are wound partly in shunt and partly in series with the armature1 in such a manner that the strength of the field-magnets and the electromotive force of the current do not vary much1 whatever be the number of lamps in circuit4 ,in alternate current machines the electromotive force keeps constant1 as the field- magnets are excited by a separate machine1 giving a continuous current4 ,we have already seen that the action of the dynamo is reversible1 and that just as a wire moved across a magnetic field supplies an electric current1 so a wire at rest1 but conducting a current across a magnetic field1 will move4 ,the electric motor is therefore essentially a dynamo1 which on being traversed by an electric current from an external source puts itself in motion4 ,thus1 if a current be sent through the armature of the ,gramme machine1 shown in figure #da1 the armature will revolve1 and the spindle1 by means of a belt on the pulley ,p1 can communicate its energy to another machine4 ,hence the electric motor can be employed to work lathes1 hoists1 lifts1 drive the screws of boats or the wheels of carriages1 and for many other purposes4 ,there are numerous types of electric motor as of the dynamo in use1 but they are all modifications of the simple continuous or alternating current dynamo4 ,obviously1 since mechanical power can be converted into electricity by the dynamo1 and reconverted into mechanical power by the motor1 it is sufficient to connect a dynamo and motor together by insulated wire in order to transmit mechanical power1 whether it be derived from wind1 water1 or fuel1 to any reasonable distance4 ,,chapter ,v4 ,,electrolysis4 ,having seen how electricity can be generated and stored in considerable quantity1 let us now turn to its practical uses4 ,of these by far the most important are based on its property of developing light and heat as in the electric spark1 chemical action as m the voltameter1 and magnetism as in the electromagnet4 ,the words current1 pressure1 and so on point to a certain analogy between electricity and water1 which helps the imagination to figure what can neither be seen nor handled1 though it must not be traced too far4 ',water1 for example1 runs by the force of gravity from a place of higher to a place of lower level4 ,the pressure of the stream is greater the more the difference of level or head of water ,the strength of the current or quantity of water flowing per second is greater the higher the pressure1 and the less the resistance of its channel4 ,the power of the water or its rate of doing mechanical work is greater the higher the pressure and the stronger the current4 ,so1 too1 electricity flows by the electromotive force from a place of higher to a place of lower electric level or potential4 ,the electric pressure is greater the more the difference of potential or electromotive force4 ,the strength of the electric current or quantity of electricity flowing per second is greater the higher the pressure or electromotive force and the less the resistance of the circuit ,the power of the electricity or its rate of doing work is greater the higher the electromotive force and the stronger the current4 ,it follows that a small quantity of water or electricity at a high pressure will give us the same amount of energy as a large quantity at a low pressure1 and our choice of one or the other will depend on the purpose we have in view4 ,as a rule1 however1 a large current at a comparatively low or moderate pressure is found the more convenient in practice4 ,the electricity of friction belongs to the former category1 and the electricity of chemistry1 heat1 and magnetism to the latter4 ,the spark of a factional or influence machine can be compared to a highland cataract of lofty height but small volume1 which is more picturesque than useful1 and the current from a voltaic battery1 a thermopile1 or a dynamo to a lowland river which can be dammed to turn a mill4 ,it is the difference between a skittish gelding and a tame carthorse4 ,not the spark from an induction coil or ,leyden jar1 but a strong and steady current at a low pressure1 is adapted for electrolysis or electrodeposition1 and hence the voltaic battery or a special form of dynamo is usually employed in this work4 ,a flash of lightning is the very symbol of terrific power1 and yet1 according to the illustrious ,faraday1 it contains a smaller amount of electricity than the feeble current required to decompose a single drop of rain4 ,in our simile of the mill dam and the battery or dynamo1 the dam corresponds to the positive pole and the river or sea below the mill to the negative pole4 ,the mill-race will stand for the wire joining the poles1 that is to say1 the external circuit1 and the mill-wheel for the work to be done in the circuit1 whether it be a chemical for decomposition1 a telegraph instrument1 an electric lamp1 or any other appliance4 ,as the current in the race depends on the head of water1 or difference of level between the dam and the sea as well as on the resistance of the channel1 so the current in the circuit depends on the electromotive force1 or difference of potential between the positive and negative poles1 as well as on the resistance of the circuit4 ,the relation between these is expressed by the well-known law of ,ohm1 which runs3 ,a current of electricity is directly proportional to the electromotive force and inversely proportional to the resistance of the circuit4 ,in practice electricity is measured by various units or standards named after celebrated electricians4 ,thus the unit of quantity is the coulomb1 the unit of current or quantity flowing per second is the ampere1 the unit of electromotive force is the volt1 and the unit of resistance is the ohm4 ,the quantity of water or any other electrolyte decomposed by electricity is proportional to the strength of the current4 ,one ampere decomposes 4#jjjjicbd gramme of water per second1 liberating 4#jjjjajchd gramme of hydrogen and 4#jjjjhbhf gramme of oxygen4 ,the quantity in grammes of any other chemical element or ion which is liberated from an electrolyte or body capable of electrochemical decomposition in a second by a current of one ampere is given by what is called the electrochemical equivalent of the ion4 ,this is found by multiplying its ordinary chemical equivalent or combining weight by 4#jjjjajchd1 which is the electrochemical equivalent of hydrogen4 ,thus the weight of metal deposited from a solution of any of its salts by a current of so many amperes in so many seconds is equal to the number of amperes multiplied by the number of seconds1 and by the electrochemical equivalent of the metal4 ,the deposition of a metal from a solution of its salt is very easily shown in the case of copper4 ,in fact1 we have already seen that in the ,daniell cell the current decomposes a solution of sulphate of copper and deposits the pure metal on the copper plate4 ,if we simply make a solution of blue vitriol in a glass beaker and dip the wires from a voltaic cell into it1 we shall find the wire from the negative pole become freshly coated with particles of new copper4 ,the sulphate has been broken up1 and the liberated metal1 being positive1 gathers on the negative electrode4 ,moreover1 if we examine the positive electrode we shall find it slightly eaten away1 because the sulphuric acid set free from the sulphate has combined with the particles of that wire to make new sulphate4 ,thus the copper is deposited on one electrode1 namely1 the cathode1 by which the current leaves the bath1 and at the expense of the other electrode1 that is to say1 the anode1 by which the current enters the bath4 ,the fact that the weight of metal deposited in this way from its salts is proportional to the current1 has been utilised for measuring the strength of currents with a fine degree of accuracy4 ,if1 for example1 the tubes of the voltameter described on page #ch were graduated1 the volume of gas evolved would be a measure of the current4 ,usually1 however1 it is the weight of silver or copper deposited from their salts in a certain time which gives the current in amperes4 ,electro-plating is the principal application of this chemical process4 ,in #ahje ,brugnatelli took a silver medal and coated it with gold by making it the cathode in a solution of a salt of gold1 and using a plate of gold for the anode4 ,the shops of our jewellers are now bright with teapots1 salt cellars1 spoons1 and other articles of the table made of inferior metals1 but beautified and preserved from rust in this way4 ,figure #dd illustrates an electro-plating bath in which a number of spoons are being plated4 ,a portion of the vat ,v is cut away to show the interior1 which contains a solution ,s of the double cyanide of gold and potassium when gold is to be laid1 and the double cyanide of silver and potassium when silver is to be deposited4 ,the electrodes are hung from metal rods1 the anode ,a being a plate of gold or silver ,g1 as the case may be1 and the cathode ,c the spoons in question4 ,when the current of the battery or dynamo passes through the bath from the anode to the cathode1 gold or silver is deposited on the spoons1 and the bath recuperates its strength by consuming the gold or silver plate4 ,enormous quantities of copper are now deposited in a similar way1 sulphate of copper being the solution and a copper plate the anode4 ,large articles of iron1 such as the parts of ordnance1 are sometimes copper-plated to preserve them from the action of the atmosphere4 ,seamless copper pipes for conveying steam1 and wires of pure copper for conducting electricity1 are also deposited1 and it is not unlikely that the kettle of the future will be made by electrolysis4 ,nickel-plating is another extensive branch of the industry1 the white nickel forming a cloak for metals more subject to corrosion4 ,nickel is found to deposit best from a solution of the double sulphate of nickel and ammonia4 ,aluminium1 however1 has not yet been successfully deposited by electricity4 ,in #ahcf ,de la ,rue observed that copper laid in this manner on another surface took on its under side an accurate impression of that surface1 even to the scratches on it1 and three years later ,jacobi1 of ,st4 ,petersburg1 and ,jordan1 of ,london1 applied the method to making copies or replicas of medals and woodcuts4 ,even non-metallic surfaces could be reproduced in copper by taking a cast of them in wax and lining the mould with fine plumbago1 which1 being a conductor1 served as a cathode to receive the layer of metal4 ,it is by the process of electrotyping or galvano- plastics that the copper faces for printing woodcuts are prepared1 and copies made of seals or medals4 ,natural objects1 such as flowers1 ferns1 leaves1 feathers1 insects1 and lizards1 can be prettily coated with bronze or copper1 not to speak of gold and silver1 by a similar process4 ,they are too delicate to be coated with black lead in order to receive the skin of metal1 but they can be dipped in solutions1 leaving a film which can be reduced to gold or silver4 ,for instance1 they may be soaked in an alcoholic solution of nitrate of silver1 made by shaking #b parts of the crystals in #ajj parts of alcohol in a stoppered bottle4 ,when dry1 the object should be suspended under a glass shade and exposed to a stream of sulphuretted hydrogen gas2 or it may be immersed in a solution of #a part of phosphorus in #ae parts of bisulphide of carbon1 #a part of bees-wax1 #a part of spirits of turpentine1 #a part of asphaltum1 and #a_/h part of caoutchouc dissolved in bisulphide of carbon4 ,this leaves a superficial film which is metallised by dipping in a solution of #bj grains of nitrate of silver to a pint of water4 ,on this metallic film a thicker layer of gold and silver in different shades can be deposited by the current1 and the silver surface may also be oxidised by washing it in a weak solution of platinum chloride4 ,electrolysis is also used to some extent in reducing metals from their ores1 in bleaching fibre1 in manufacturing hydrogen and oxygen from water1 and in the chemical treatment of sewage4 ,,chapter ,,vi4 ,,the ,,telegraph ,,and ,,telephone4 ,like the philosopher's stone1 the elixir of youth1 and perpetual motion1 the telegraph was long a dream of the imagination4 ,in the sixteenth century1 if not before1 it was believed that two magnetic needles could be made sympathetic1 so that when one was moved the other would likewise move1 however far apart they were1 and thus enable two distant friends to communicate their minds to one another4 ,the idea was prophetic1 although the means of giving effect to it were mistaken4 ,it became practicable1 however1 when ,oersted discovered that a magnetic needle could be swung to one side or the other by an electric current passing near it4 ,the illustrious ,laplace was the first to suggest a telegraph on this principle4 ,a wire connecting the two poles of a battery is traversed1 as we know1 by an electric current1 which makes the round of the circuit1 and only flows when that circuit is complete4 ,however long the wire may be1 however far it may run between the poles1 the current will follow all its windings1 and finish its course from pole to pole of the battery4 ,you may lead the wire across the ocean and back1 or round the world if you will1 and the current will travel through it4 ,the moment you break the wire or circuit1 however1 the current will stop4 ,by its electromotive force it can overcome the resistance of the many miles of conductor2 but unless it be unusually strong it cannot leap across even a minute gap of air1 which is one of the best insulators4 ,if1 then1 we have a simple device easily manipulated by which we can interrupt the circuit of the battery1 in accordance with a given code1 we shall be able to send a series of currents through the wire and make sensible signals wherever we choose4 ,these signs can be produced by the deviation of a magnetic needle1 as ,laplace pointed out1 or by causing an electro-magnet to attract soft iron1 or by chemical decomposition1 or any other sensible effect of the current4 ,ampere developed the idea of ,laplace into a definite plan1 and in #ahcj or thereabout ,ritchie1 in ,london1 and ,baron ,schilling1 in ,st4 ,petersburg1 exhibited experimental models4 ,in #ahcc and afterwards ,professors ,gauss and ,weber installed a private telegraph between the observatory and the physical cabinet of the ,university of ,gottingen4 ,moreover1 in #ahcf ,william ,fothergill ,cooke1 a retired surgeon of the ,madras army1 attending lectures on anatomy at the ,university of ,heidelberg1 saw an experimental telegraph of ,professor ,moncke1 which turned all his thoughts to the subject4 ,on returning to ,london he made the acquaintance of ,professor ,wheatstone1 of ,king's ,college1 who was also experimenting in this direction1 and in #ahcf they took out a patent for a needle telegraph4 ,it was tried successfully between the ,euston terminus and the ,camden ,town station of the ,london and ,north-,western ,railway on the evening of ,july #beth1 #ahcg1 in presence of ,mr4 ,robert ,stephenson1 and other eminent engineers4 ,wheatstone1 sitting in a small room near the booking-office at ,euston1 sent the first message to ,cooke at ,camden ,town1 who at once replied4 ,never1 said ,wheatstone1 did ,i feel such a tumultuous sensation before1 as when1 all alone in the still room1 ,i heard the needles click1 and as ,i spelled the words ,i felt all the magnitude of the invention pronounced to be practicable without cavil or dispute4 ,the importance of the telegraph in working railways was manifest1 and yet the directors of the company were so purblind as to order the removal of the apparatus1 and it was not until two years later that the ,great ,western ,railway ,company adopted it on their line from ,paddington to ,west ,drayton1 and subsequently to ,slough4 ,this was the first telegraph for public use1 not merely in ,england1 but the world4 ,the charge for a message was only a shilling1 nevertheless few persons availed themselves of the new invention1 and it was not until its fame was spread abroad by the clever capture of a murderer named ,tawell that it began to prosper4 ,tawell had killed a woman at ,slough1 and on leaving his victim took the train for ,paddington4 ,the police1 apprised of the murder1 telegraphed a description of him to ,london4 ,the original five needle instrument1 now in the museum of the ,post ,office1 had a dial in the shape of a diamond1 on which were marked the letters of the alphabet1 and each letter of a word was pointed out by the movements of a pair of needles4 ,the dial had no letter q1 and as the man was described as a quaker the word was sent kwaker4 ,when the tram arrived at ,paddington he was shadowed by detectives1 and to his utter astonishment was quietly arrested in a tavern near ,cannon ,street4 ,in ,cooke and ,wheatstone's early telegraph the wire travelled the whole round of the circuit1 but it was soon found that a return wire in the circuit was unnecessary1 since the earth itself could take the place of it4 ,one wire from the sending station to the receiving station was sufficient1 provided the apparatus at each end were properly connected to the ground4 ,this use of the earth not only saved the expense of a return wire1 but diminished the resistance of the circuit1 because the earth offered practically no resistance4 ,figure #de is a diagram of the connections in a simple telegraph circuit4 ,at each of the stations there is a battery ,b ,b'1 an interruptor or sending key ,k ,k'to make and break the continuity of the circuit1 a receiving instrument ,r ,r'to indicate the signal currents by their sensible effects1 and connections with ground or earth plates ,e ,e' to engage the earth as a return wire4 ,these are usually copper plates buried in the moist subsoil or the water pipes of a city4 ,the line wire is commonly of iron supported on poles1 but insulated from them by earthenware cups or insulators4 ,at the station on the left the key is in the act of ,,sending a message1 and at the post on the right it is conformably in the position for receiving the message4 ,the key is so constructed that when it is at rest it puts the line in connection with the earth through the ,,receiving ,,instrument and the earth plate4 ,the key ,k consists essentially of a spring-lever1 with two platinum contacts1 so placed that when the lever is pressed down by the hand of the telegraphist it breaks contact with the receiver ,r1 and puts the line-wire ,l in connection with the earth ,e through the battery ,b1 as shown on the left4 ,a current then flows into the line and traverses the receiver ,r' at the distant station1 returning or seeming to return to the sending battery by way of the earth plate ,e' on the right and the intermediate ground4 ,the duration of the current is at the will of the operator who works the sending-key1 and it is plain that signals can be made by currents of various lengths4 ,in the ,morse code of signals1 which is now universal1 only two lengths of current are employed-- namely1 a short1 momentary pulse1 produced by instant contact of the key1 and a jet given by a contact about three times longer4 ,these two signals are called dot and dash1 and the code is merely a suitable combination of them to signify the several letters of the alphabet4 ,thus e1 the commonest letter in ,english1 is telegraphed by a single dot1 and the letter t by a single dash1 while the letter a is indicated by a dot followed after a brief interval or space by a dash4 ,obviously1 if two kinds of current are used1 that is to say1 if the poles of the battery are reversed by the sending-key1 and the direction of the current is consequently reversed in the circuit1 there is no need to alter the length of the signal currents1 because a momentary current sent in one direction will stand for a dot and in the other direction for a dash4 ,as a matter of fact1 the code is used in both ways1 according to the nature of the line and receiving instrument4 ,on submarine cables and with needle and mirror instruments1 the signals are made by reversing currents of equal duration1 but on land lines worked by ,morse instruments and sounders1 they are produced by short and long currents4 ,the ,morse code is also used in the army for signalling by waving flags or flashing lights1 and may also be serviceable in private life4 ,telegraph clerks have been known to speak with each other in company by winking the right and left eye1 or tapping with their teaspoon on a cup and saucer4 ,any two distinct signs1 however made1 can be employed as a telegraph by means of the ,morse code1 which runs as shown in figure #df4 ,the receiving instruments ,r ,r' may consist of a magnetic needle pivotted on its centre and surrounded by a coil of wire1 through which the current passes and deflects the needle to one side or the other1 according to the direction in which it flows4 ,such was the pioneer instrument of ,cooke and ,wheatstone1 which is still employed in ,england in a simplified form as the single and double needle-instrument on some of the local lines and in railway telegraphs4 ,the signals are made by sending momentary currents in opposite directions by a double current key1 which 7unlike the key ,k in figure #de7 reverses the poles ,a 4- ,j -4-4 ,b -444 ,k -4- ,c 444 ,l -- ,d -44 ,m - - ,e 4 ,n -4 ,f 4-4 ,o 4 4 ,g --4 ,q 44-4 ,h 4 44 ,r 4 44 ,i 44 ,s 444 #a 4--4 ,t - #b 44-44 ,u 44- #c 444-4 ,v 444- #d 4444- ,w 4- #e --- ,x 4-44 #f 444444 ,y 44 44 #g --44 ,z 444 4 #h -44 44 4 44 #i -44- ,period 44--44 #j ---- ,comma 4-4- ,the ,international 7,morse7 code used elsewhere is the same as the above1 with the following exceptions3 ,c -4-4 ,q --4- ,f 4 -4 ,r 4-4 ,j 4--- ,x -44- ,l 4-44 ,y -4-- ,o --- ,z --44 ,p 4--4 ,,fig4 #df4--,morse ,signal ,alphabet4 of the battery1 in putting the line to one or the other1 and thus making the dot signal with the positive and the dash signal with the negative pole4 ,it follows that if the dot is indicated by a throw of the needle to the right side1 a dash will be given by a throw to the left4 ,most of the telegraph instruments for land lines are based on the principle of the electro-magnet4 ,we have already seen 7page #ei7 how ,ampere found that a spiral of wire with a current flowing in it behaved like a magnet and was able to suck a piece of soft iron into it4 ,if the iron is allowed to remain there as a core1 the combination of coil and core becomes an electro-magnet1 that is to say1 a magnet which is only a magnet so long as the current passes4 ,figure #dg represents a simple horse-shoe electro-magnet as invented by ,sturgeon4 ,a ,u-shaped core of soft iron is wound with insulated wire ,w1 and when a current is sent through the wire1 the core is found to become magnetic with a north pole in one end and a south pole in the other4 ,these poles are therefore able to attract a separate piece of soft iron or armature ,a4 ,when the current is stopped1 however1 the core ceases to be a magnet and the armature drops away4 ,in practice the electromagnet usually takes the form shown in figure #dh1 where the poles are two bobbins or solenoids of wire #fa having straight cores of iron which are united by an iron bar ,b1 and ,a is the armature4 ,such an electromagnet is a more powerful device than a swinging needle1 and better able to actuate a mechanism4 ,it became the foundation of the recording instrument of ,samuel ,morse1 the father of the telegraph in ,america4 ,the ,morse1 or1 rather1 ,morse and ,vail instrument1 actually marks the signals in dots and dashes on a ribbon of moving paper4 ,figure #di represents the ,morse instrument1 in which an electromagnet ,m attracts an iron armature ,a when a current passes through its bobbins1 and by means of a lever ,l connected with the armature raises the edge of a small disc out of an ink-pot ,i against the surface of a travelling slip of paper ,p1 and marks a dot or dash upon it as the case may be4 ,the rest of the apparatus consists of details and accessories for its action and adjustment1 together with the sending-key ,k1 which is used in asking for repetitions of the words1 if necessary4 ,a permanent record of the message is of course convenient1 nevertheless the operators prefer to read the signals by the ear1 rather than the eye1 and1 to the annoyance of ,morse1 would listen to the click of the marking disc rather than decipher the marks on the paper4 ,consequently ,alfred ,vail1 the collaborator of ,morse1 who really invented the ,morse code1 produced a modification of the recording instrument working solely for the ear4 ,the sounder1 as it is called1 has largely driven the printer from the field4 ,this neat little instrument is shown in figure #ej1 where ,m is the electromagnet1 and ,a is the armature which chatters up and down between two metal stops1 as the current is made and broken by the sending-key1 and the operator listening to the sounds interprets the message letter by letter and word by word4 ,the motion of the armature in both of these instruments takes a sensible time1 but ,alexander ,bain1 of ,thurso1 by trade a watchmaker1 and by nature a genius1 invented a chemical telegraph which was capable of a prodigious activity4 ,the instrument of ,bain resembled the ,morse in marking the signals on a tape of moving paper1 but this was done by electrolysis or electro-chemical decomposition4 ,the paper was soaked in a solution of iodide of potassium in starch and water1 and the signal currents were passed through it by a marking stylus or pencil of iron4 ,the electricity decomposed the solution in its passage and left a blue stain on the paper1 which corresponded to the dot and dash of the ,morse apparatus4 ,the ,bain telegraph can record over #ajjj words a minute as against #dj to #ej by the ,morse or sounder1 nevertheless it has fallen into disuse1 perhaps because the solution was troublesome4 ,it is stated that a certain blind operator could read the signals by the smell of the chemical action2 and we can well believe it4 ,in fact1 the telegraph appeals to every sense1 for a deaf clerk can feel the movements of a sounder1 and the signals of the current can be told without any instrument by the mere taste of the wires inserted in the mouth4 ,a skilful telegraphist can transmit twenty-five words a minute with the single-current key1 and nearly twice as many by the double-current key1 and if we remember that an average ,english word requires fifteen separate signals1 the number will seem remarkable2 but by means of ,wheatstone's automatic sender #aej words or more can be sent in a minute4 ,among telegraphs designed to print the message in ,roman type1 that of ,professor ,david ,edward ,hughes is doubtless the fittest1 since it is now in general use on the ,continent1 and conveys our ,continental news4 ,in this apparatus the electromagnet1 on attracting its armature1 presses the paper against a revolving type wheel and receives the print of a type1 so that the message can be read by a novice4 ,to this effect the type wheel at the receiving station has to keep in perfect time as it revolves1 so that the right letter shall be above the paper when the current passes4 ,small varieties of the type-printer are employed for the distribution of news and prices in most of the large towns1 being located in hotels1 restaurants1 saloons1 and other public places1 and reporting prices of stocks and bonds1 horse races1 and sporting and general news4 ,the duplex system1 whereby two messages1 one in either direction1 can be sent over one wire simultaneously without interfering1 and the quadruplex system1 whereby four messages1 two in either direction1 are also sent at once1 have come into use where the traffic over the lines is very great4 ,both of these systems and their modifications depend on an ingenious arrangement of the apparatus at each end of the line1 by which the signal currents sent out from one station do not influence the receivers there1 but leave them free to indicate the currents from the distant station4 ,when the ,wheatstone ,automatic ,sender is employed with these systems about #ejj words per minute can be sent through the line4 ,press news is generally sent by night1 and it is on record1 that during a great debate in ,parliament1 as many as half a million words poured out of the ,central ,telegraph ,station at ,st4 ,martin's-le-,grand in a single night to all parts of the country4 ,errors occur now and then through bad penmanship or the similarity of certain signals1 and amusing telegrams have been sent out1 as when the nomination of ,mr4 ,brand for the ,speakership of the ,commons took the form of ,proposed to brand ,speaker2 and an excursion party assured their friends at home of their security by the message1 ,arrived all tight4 ,telegraphs1 in the literal sense of the word1 which actually write the message as with a pen1 and make a copy or facsimile of the original1 have been invented from time to time4 ,such are the telegraphic pen of ,mr4 ,e4 ,a4 ,cowper1 and the telautographs of ,mr4 ,j4 ,h4 ,robertson and ,mr4 ,elisha ,gray4 ,the first two are based on a method of varying the strength of the current in accordance with the curves of the handwriting1 and making the varied current actuate by means of magnetism a writing pen or stylus at the distant station4 ,the instrument of ,gray1 which is the most successful1 works by intermittent currents or electrical impulses1 that excite electro-magnets and move the stylus at the far end of the line4 ,they are too complicated for description here1 and are not of much practical importance4 ,telegraphs for transmitting sketches and drawings have also been devised by ,d',ablincourt and others1 but they have not come into general use4 ,of late another step forward has been taken by ,mr4 ,amstutz1 who has invented an apparatus for transmitting photographic pictures to a distance by means of electricity4 ,the system may be described as a combination of the photograph and telegraph4 ,an ordinary negative picture is taken1 and then impressed on a gelatine plate sensitised with bichromate of potash4 ,the parts of the gelatine in light become insoluble1 while the parts in shade can be washed away by water4 ,in this way a relief or engraving of the picture is obtained on the gelatine1 and a cross section through the plate would1 if looked at edgeways1 appear serrated1 or up and down1 like a section of country or the trace of the stylus in the record of a phonograph4 ,the gelatine plate thus carved by the action of light and water is wrapped round a revolving drum or barrel1 and a spring stylus or point is caused to pass over it as the barrel revolves1 after the manner of a phonographic cylinder4 ,in doing so the stylus rises and falls over the projections in the plate and works a lever against a set of telegraph keys1 which open electric contacts and break the connections of an electric battery which is joined between the keys and the earth4 ,there are four keys1 and when they are untouched the current splits up through four by-paths or bobbins of wire before it enters the line wire and passes to the distant station4 ,when any of the keys are touched1 however1 the corresponding by-path or bobbin is cut out of circuit4 ,the suppression of a by-path or channel for the current has the effect of adding to the resistance of the line1 and therefore of diminishing the strength of the current4 ,when all the keys are untouched the resistance is least and the current strongest4 ,on the other hand1 when all the keys but the last are touched1 the resistance is greatest and the current weakest4 ,by this device it is easy to see that as the stylus or tracer sinks into a hollow of the gelatine1 or rises over a height1 the current in the line becomes stronger or weaker4 ,at the distant station the current passes through a solenoid or hollow coil of wire connected to the earth and magnetises it1 so as to pull the soft iron plug or core with greater or less force into its hollow interior4 ,the up and down movement of the plug actuates a graving stylus or point through a lever1 and engraves a copy of the original gelatine trace on the surface of a wax or gelatine plate overlying another barrel or drum1 which revolves at a rate corresponding to that of the barrel at the transmitting station4 ,in this way a facsimile of the gelatine picture is produced at the distant station1 and an electrotype or cliche of it can be made for printing purposes4 ,the method is1 in fact1 a species of electric line graving1 and ,mr4 ,amstutz hopes to apply it to engraving on gold1 silver1 or any soft metal1 not necessarily at a distance4 ,we know that an electric current in one wire can induce a transient current in a neighbouring wire1 and the fact has been utilised in the ,united ,states by ,phelps and others to send messages from moving trains4 ,the signal currents are intermittent1 and when they are passed through a conductor on the train they excite corresponding currents in a wire run along the track1 which can be interpreted by the hum they make in a telephone4 ,experiments recently made by ,mr4 ,w4 ,h4 ,preece for the ,post ,office show that with currents of sufficient strength and proper apparatus messages can be sent through the air for five miles or more by this method of induction4 ,we come now to the submarine telegraph1 which differs in many respects from the overland telegraph4 ,obviously1 since water and moist earth is a conductor1 a wire to convey an electric current must be insulated if it is intended to lie at the bottom of the sea or buried underground4 ,the best materials for the purpose yet discovered are gutta-percha and india-rubber1 which are both flexible and very good insulators4 ,the first submarine cable was laid across the ,channel from ,dover to ,calais in #ahea1 and consisted of a copper strand1 coated with gutta-percha1 and protected from injury by an outer sheath of hemp and iron wire4 ,it is the general type of all the submarine cables which have been deposited since then in every part of the world4 ,as a rule1 the armour or sheathing is made heavier for shore water than it is for the deep sea1 but the electrical portion1 or core1 that is to say1 the insulated conductor1 is the same throughout4 ,the first ,atlantic cable was laid in #aheh by ,cyrus ,w4 ,field and a company of ,british capitalists1 but it broke down1 and it was not until #ahff that a new and successful cable was laid to replace it4 ,figure #ea represents various cross-sections of an ,atlantic cable deposited in #ahid4 ,the inner star of twelve copper wires is the conductor1 and the black circle round it is the gutta-percha or insulator which keeps the electricity from escaping into the water4 ,the core in shallow water is protected from the bites of teredoes by a brass tape1 and the envelope or armour consists of hemp and iron wire preserved from corrosion by a covering of tape and a compound of mineral pitch and sand4 ,the circuit of a submarine line is essentially the same as that of a land line1 except that the earth connection is usually the iron sheathing of the cable in lieu of an earth-plate4 ,on a cable1 however1 at least a long cable1 the instruments for sending and receiving the messages are different from those employed on a land line4 ,a cable is virtually a ,leyden jar or condenser1 and the signal currents in the wire induce opposite currents in the water or earth4 ,as these charges hold each other the signals are retarded in their progress1 and altered from sharp sudden jets to lagging undulations or waves1 which tend to run together or coalesce4 ,the result is that the separate signal currents which enter a long cable issue from it at the other end in one continuous current1 with pulsations at every signal1 that is to say1 in a lapsing stream1 like a jet of water flowing from a constricted spout4 ,the receiving instrument must be sufficiently delicate to manifest every pulsation of the current4 ,its indicator1 in fact1 must respond to every rise and fall of the current1 as a float rides on the ripples of a stream4 ,such an instrument is the beautiful mirror galvanometer of ,lord ,kelvin1 ,ex-,president of the ,royal ,society1 which we illustrate in figure #eb1 where ,c is a coil of wire with a small magnetic needle suspended in its heart1 and ,d is a steel magnet supported over it4 ,the needle 7,m figure #ec7 is made of watch spring cemented to the back of a tiny mirror the size of a half-dime which is hung by a single fibre of floss silk inside an air cell or chamber with a glass lens ,g in front1 and the coil ,c surrounds it4 ,a ray of light from a lamp ,l 7figure #eb7 falls on the mirror1 and is reflected back to a scale ,s1 on which it makes a bright spot4 ,now1 when the coil ,c is connected between the end of the cable and the earth1 the signal current passing through it causes the tiny magnet to swing from side to side1 and the mirror moving with it throws the beam up and down the scale4 ,the operator sitting by watches the spot of light as it flits and flickers like a fire-fly in the darkness1 and spells out the mysterious message4 ,a condenser joined in the circuit between the cable and the receiver1 or between the receiver and the earth1 has the effect of sharpening the waves of the current1 and consequently of the signals4 ,the double-current key1 which reverses the poles of the battery and allows the signal currents to be of one length1 that is to say1 all dots1 is employed to send the message4 ,another receiving instrument employed on most of the longer cables is the siphon recorder of ,lord ,kelvin1 shown in figure #ed1 which marks or writes the message on a slip of travelling paper4 ,essentially it is the inverse of the mirror instrument1 and consists of a light coil of wire ,s suspended in the field between the poles of a strong magnet ,m4 ,the coil is attached to a fine siphon 7,t#e7 filled with ink1 and sometimes kept in vibration by an induction coil so as to shake the ink in fine drops upon a slip of moving paper4 ,the coil is connected between the cable and the earth1 and1 as the signal current passes through1 it swings to one side or the other1 pulling the siphon with it4 ,the ink1 therefore1 marks a wavy line on the paper1 which is in fact a delineation of the rise and fall of the signal current and a record of the message4 ,the dots in this case are represented by the waves above1 and the dashes by the waves below the middle line1 as may be seen in the following alphabet1 which is a copy of one actually written by the recorder on a long submarine cable4 ,owing to induction1 the speed of signalling on long cables is much slower than on land lines of the same length1 and only reaches from #be to #de words a minute on the ,atlantic cables1 or #cj to #ej words with an automatic sending-key2 but this rate is practically doubled by employing the ,muirhead duplex system of sending two messages1 one from each end1 at the same time4 ,the relation of the telegraph to the telephone is analogous to that of the lower animals and man4 ,in a telegraph circuit1 with its clicking key at one end and its chattering sounder at the other1 we have1 in fact1 an apish forerunner of the exquisite telephone1 with its mysterious microphone and oracular plate4 ,nevertheless1 the telephone descended from the telegraph in a very indirect manner1 if at all1 and certainly not through the sounder4 ,the first practical suggestion of an electric telephone was made by ,m4 ,charles ,bourseul1 a ,french telegraphist1 in #ahed1 but to all appearance nothing came of it4 ,in #ahfj1 however1 ,philipp ,reis1 a ,german schoolmaster1 constructed a rudimentary telephone1 by which music and a few spoken words were sent4 ,finally1 in #ahgf1 ,mr4 ,alexander ,graham ,bell1 a ,scotchman1 residing in ,canada1 and subsequently in the ,united ,states1 exhibited a capable speaking telephone of his invention at the ,centennial ,exhibition1 ,philadelphia4 ,figure #ef represents an outside view and section of the ,bell telephone as it is now made1 where ,m is a bar magnet having a small bobbin or coil of fine insulated wire ,c girdling one pole4 ,in front of this coil there is a circular plate of soft iron capable of vibrating like a diaphragm or the drum of the ear4 ,a cover shaped like a mouthpiece ,o fixes the diaphragm all round1 and the wires ,w ,w serve to connect the coil in the circuit4 ,the soft iron diaphragm is1 of course1 magnetised by the induction of the pole1 and would be attracted bodily to the pole were it not fixed by the rim1 so that only its middle is free to move4 ,now1 when a person speaks into the mouthpiece the sonorous waves impinge on the diaphragm and make it vibrate in sympathy with them4 ,being magnetic1 the movement of the diaphragm to and from the bobbin excites corresponding waves of electricity in the coil1 after the famous experiment of ,faraday 7page #fd74 ,if this undulatory current is passed through the coil of a similar telephone at the far end of the line1 it will1 by a reverse action1 set the diaphragm in vibration and reproduce the original sonorous waves4 ,the result is1 that when another person listens at the mouthpiece of the receiving telephone1 he will hear a faithful imitation of the original speech4 ,the ,bell telephone is virtually a small magneto-electric generator of electricity1 and when two are joined in circuit we have a system for the transmission of energy4 ,as the voice is the motive power1 its talk1 though distinct1 is comparatively feeble1 and further improvements were made before the telephone became as serviceable as it is now4 ,edison1 in #ahgg1 was the first to invent a working telephone1 which1 instead of generating the current1 merely controlled the strength of it1 as the sluice of a mill-dam regulates the flow of water in the lead4 ,du ,moncel had observed that powder of carbon altered in electrical resistance under pressure1 and ,edison found that lamp-black was so sensitive as to change in resistance under the impact of the sonorous waves4 ,his transmitter consisted of a button or wafer of lamp-black behind a diaphragm1 and connected in the circuit4 ,on speaking to the diaphragm the sonorous waves pressed it against the button1 and so varied the strength of the current in a sympathetic manner4 ,the receiver of ,edison was equally ingenious1 and consisted of a cylinder of prepared chalk kept in rotation and a brass stylus rubbing on it4 ,when the undulatory current passed from the stylus to the chalk1 the stylus slipped on the surface1 and1 being connected to a diaphragm1 made it vibrate and repeat the original sounds4 ,this electro- motograph receiver was1 however1 given up1 and a combination of the ,edison transmitter and the ,bell receiver came into use4 ,at the end of #ahgg ,professor ,d4 ,e4 ,hughes1 a distinguished ,welshman1 inventor of the printing telegraph1 discovered that any loose contact between two conductors had the property of transmitting sounds by varying the strength of an electric current passing through it4 ,two pieces of metal--for instance1 two nails or ends of wire--when brought into a loose or crazy contact under a slight pressure1 and traversed by a current1 will transmit speech4 ,two pieces of hard carbon are still better than metals1 and if properly adjusted will make the tread of a fly quite audible in a telephone connected with them4 ,such is the famous microphone1 by which a faint sound can be magnified to the ear4 ,figure #eg represents what is known as the pencil microphone1 in which ,m is a pointed rod of hard carbon1 delicately poised between two brackets of carbon1 which are connected in circuit with a battery ,b and a ,bell telephone ,t4 ,the joints of rod and bracket are so sensitive that the current flowing across them is affected in strength by the slightest vibration1 even the walking of an insect4 ,if1 therefore1 we speak near this microphone1 the sonorous waves1 causing the pencil to vibrate1 will so vary the current in accordance with them as to reproduce the sounds of the voice in the telephone4 ,the true nature of the microphone is not yet known1 but it is evident that the air or ether between the surfaces in contact plays an important part in varying the resistance1 and1 therefore1 the current4 ,in fact1 a small voltaic arc1 not luminous1 but dark1 seems to be formed between the points1 and the vibrations probably alter its length1 and1 consequently1 its resistance4 ,the fact that a microphone is reversible and can act as a receiver1 though a poor one1 tends to confirm this theory4 ,moreover1 it is not unlikely that the slipping of the stylus in the electromotograph is due to a similar cause4 ,be this as it may1 there can be no doubt that carbon powder and the lamp-black of the ,edison button are essentially a cluster of microphones4 ,many varieties of the ,hughes microphone under different names are now employed as transmitters in connection with the ,bell telephone4 ,figure #eh represents a simple micro-telephone circuit1 where ,m is the ,hughes microphone transmitter1 ,t the ,bell telephone receiver1 ,,jb the battery1 and ,e ,e the earth-plates2 but sometimes a return wire is used in place of the earth4 ,the line wire is usually of copper and its alloys1 which are more suitable than iron1 especially for long distances4 ,just as the signal currents in a submarine cable induce corresponding currents in the sea water which retard them1 so the currents in a land wire induce corresponding currents in the earth1 but in aerial lines the earth is generally so far away that the consequent retardation is negligible except in fast working on long lines4 ,the ,bell telephone1 however1 is extremely sensitive1 and this induction affects it so much that a conversation through one wire can be overheard on a neighbouring wire4 ,moreover1 there is such a thing as self-induction in a wire--that is to say1 a current in a wire tends to induce an opposite current in the same wire1 which is practically equivalent to an increase of resistance in the wire4 ,it is particularly observed at the starting and stopping of a current1 and gives rise to what is called the extra-spark seen in breaking the circuit of an induction coil4 ,it is also active in the vibratory currents of the telephone1 and1 like ordinary induction1 tends to retard their passage4 ,copper being less susceptible of self-induction than iron1 is preferred for trunk lines4 ,the disturbing effect of ordinary induction is avoided by using a return wire or loop circuit1 and crossing the going and coming wires so as to make them exchange places at intervals4 ,moreover1 it is found that an induction coil in the telephone circuit1 like a condenser in the cable circuit1 improves the working1 and hence it is usual to join the battery and transmitter with the primary wire1 and the secondary wire with the line and the receiver4 ,the longest telephone line as yet made is that from ,new ,york to ,chicago1 a distance of #iej miles4 ,it is made of thick copper wire1 erected on cedar poles #ce feet above the ground4 ,induction is so strong on submarine cables of #ej or #ajj miles in length that the delicate waves of the telephone current are smoothed away1 and the speech is either muffled or entirely stifled4 ,nevertheless1 a telephone cable #bj miles long was laid between ,dover and ,calais in #ahia1 and another between ,stranraer and ,donaghadee more recently1 thus placing ,great ,britain on speaking terms with ,france and other parts of the ,continent4 ,figure #ei shows a form of telephone apparatus employed in the ,united ,kingdom4 ,in it the transmitter and receiver1 together with a call-bell1 which are required at each end of the line1 are neatly combined4 ,the transmitter is a ,blake microphone1 in which the loose joint is a contact of platinum on hard carbon4 ,it is fitted up inside the box1 together with an induction coil1 and ,m is the mouthpiece for speaking to it4 ,the receiver is a pair of ,bell telephones ,t ,t1 which are detached from their hooks and held to the ear4 ,a call-bell ,b serves to ring up the correspondent at the other end of the line4 ,excepting private lines1 the telephone is worked on the exchange system--that is to say1 the wires running to different persons converge in a central exchange1 where1 by means of an apparatus called a switch board1 they are connected together for the purpose of conversation ,a telephone exchange would make an excellent subject for the artist4 ,he delights to paint us a row of ,venetian bead stringers or a band of ,sevilhan cigarette makers1 but why does he shirk a bevy of industrious girls working a telephone exchange8 ,let us peep into one of these retired haunts1 where the modern ,fates are cutting and joining the lines of electric speech between man and man in a great city4 ,the scene is a long1 handsome room or gallery1 with a singular piece of furniture in the shape of an ,l occupying the middle4 ,this is the switchboard1 in which the wires from the offices and homes of the subscribers are concentrated like the nerves in a ganglion4 ,it is known as the multiple switchboard1 an ,american invention1 and is divided into sections1 over which the operators preside4 ,the lines of all the subscribers are brought to each section1 so that the operator can cross connect any two lines in the whole system without leaving her chair4 ,each section of the board is1 in fact1 an epitome of the whole1 but it is physically impossible for a single operator to make all the connections of a large exchange1 and the work is distributed amongst them4 ,a multiplicity of wires is therefore needed to connect1 say1 two thousand subscribers4 ,these are all concealed1 however1 at the back of the board1 and in charge of the electricians4 ,the young lady operators have nothing to do with these1 and so much the better for them1 as it would puzzle their minds a good deal worse than a ravelled skein of thread4 ,their duty is to sit in front of the board in comfortable seats at a long table and make the needful connections4 ,the call signal of a subscriber is given by the drop of a disc bearing his number4 ,the operator then asks the subscriber by telephone what he wants1 and on hearing the number of the other subscriber he wishes to speak with1 she takes up a pair of brass plugs coupled by a flexible conductor and joins the lines of the subscribers on the switchboard by simply thrusting the plugs into holes corresponding to the wires4 ,the subscribers are then free to talk with each other undisturbed1 and the end of the conversation is signalled to the operator4 ,every instant the call discs are dropping1 the connecting plugs are thrust into the holes1 and the girls are asking ,hullo6 hullo6 ,are you there8 ,who are you8 ,have you finished8 ,yet all this constant activity goes on quietly1 deftly --we might say elegantly--and in comparative silence1 for the low tones of the girlish voices are soft and pleasing1 and the harsher sounds of the subscriber are unheard in the room by all save the operator who attends to him4 ,,chapter ,,vii4 ,,electric ,,light ,,and ,,heat4 ,the electric spark was1 of course1 familiar to the early experimenters with electricity1 but the electric light1 as we know it1 was first discovered by ,sir ,humphrey ,davy1 the ,cornish philosopher1 in the year #ahaa or thereabout4 ,with the magic of his genius ,davy transformed the spark into a brilliant glow by passing it between two points of carbon instead of metal4 ,if1 as in figure #fj1 we twist the wires 7 and--7 which come from a voltaic battery1 say of #bj cells1 about two carbon pencils1 and bring their tips together in order to start the current1 then draw them a little apart1 we shall produce an artificial or mimic star4 ,a sheet of dazzling light1 which is called the electric arc1 is seen to bridge the gap4 ,it is not a true flame1 for there is little combustion1 but rather a nebulous blaze of silvery lustre in a bluish veil of heated air4 ,the points of carbon are white-hot1 and the positive is eaten away into a hollow or crater by the current1 which violently tears its particles from their seat and whirls them into the fierce vortex of the arc4 ,the negative remains pointed1 but it is also worn away about half as fast as the positive4 ,this wasting of the carbons tends to widen the arc too much and break the current1 hence in arc lamps meant to yield the light for hours the sticks are made of a good length1 and a self- acting mechanism feeds them forward to the arc as they are slowly consumed1 thus maintaining the splendour of the illumination4 ,many ingenious lamps have been devised by ,serrin1 ,dubosq1 ,siemens1 ,brockie1 and others1 some regulating the arc by clockwork and electro-magnetism1 or by thermal and other effects of the current4 ,they are chiefly used for lighting halls and railway stations1 streets and open spaces1 search-lights and lighthouses4 ,they are sometimes naked1 but as a rule their brightness is tempered by globes of ground or opal glass4 ,in search-lights a parabolic mirror projects all the rays in any one direction1 and in lighthouses the arc is placed in the focus of the condensing lenses1 and the beam is visible for at least twenty or thirty miles on clear nights4 ,very powerful arc lights1 equivalent to hundreds of thousands of candles1 can be seen for #ajj or #aej miles4 ,figure #fa illustrates the ,pilsen lamp1 in which the positive ,carbon ,g runs on rollers rr through the hollow interior of two solenoids or coils of wire ,,mm' and carries at its middle a spindle-shaped piece of soft iron ,c4 ,the current flows through the solenoid ,m on its way to the arc1 but a branch or shunted portion of it flows through the solenoid ,m'1 and as both of these solenoids act as electromagnets on the soft iron ,c1 each tending to suck it into its interior1 the iron rests between them when their powers are balanced4 ,when1 however1 the arc grows too wide1 and the current therefore becomes too weak1 the shunt solenoid ,m' gains a purchase over the main solenoid ,m1 and1 pulling the iron core towards it1 feeds the positive carbon to the arc4 ,in this way the balance of the solenoids is readjusted1 the current regains its normal strength1 the arc its proper width1 and the light its brilliancy4 ,figure #fb is a diagrammatic representation of the ,brush arc lamp4 ,x and ,y are the line terminals connecting the lamp in circuit4 ,on the one hand1 the current splits and passes around the hollow spools ,h ,h'1 thence to the rod ,n through the carbon ,k1 the arc1 the carbon ,k'1 and thence through the lamp frame to ,y4 ,on the other hand1 it runs in a resistance fine-wire coil around the magnet ,t1 thence to ,y4 ,the operation of the lamp is as follows3 ,k and ,k' being in contact1 a strong current starts through the lamp energising ,h and ,h'1 which suck in their core pieces ,n and ,s1 lifting ,c1 and by it the washer-clutch ,w and the rod ,n and carbon ,k1 establishing the arc4 ,k is lifted until the increasing resistance of the lengthening arc weakens the current in ,h ,h' and a balance is established4 ,as the carbons burn away1 ,c gradually lowers until a stop under ,w holds it horizontal and allows ,n to drop through ,w1 and the lamp starts anew4 ,if for any reason the resistance of the lamp becomes too great1 or the circuit is broken1 the increased current through ,t draws up its armature1 closing the contacts ,m1 thus short-circuiting the lamp through a thick1 heavy wire coil on ,t1 which then keeps ,m closed1 and prevents the dead lamp from interfering with the others on its line4 ,numerous modifications of this lamp are in very general use4 ,davy also found that a continuous wire or stick of carbon could be made white-hot by sending a sufficient current through it1 and this fact is the basis of the incandescent lamp now so common in our homes4 ,wires of platinum1 iridium1 and other inoxidisable metals raised to incandescence by the current are useful in firing mines1 but they are not quite suitable for yielding a light1 because at a very high temperature they begin to melt4 ,every solid body becomes red-hot--that is to say1 emits rays of red light1 at a temperature of about #ajjj degrees ,fahrenheit1 yellow rays at #acjj degrees1 blue rays at #aejj degrees1 and white light at #bjjj degrees4 ,it is found1 however1 that as the temperature of a wire is pushed beyond this figure the light emitted becomes far more brilliant than the increase of temperature would seem to warrant4 ,it therefore pays to elevate the temperature of the filament as high as possible4 ,unfortunately the most refractory metals1 such as platinum and alloys of platinum with iridium1 fuse at a temperature of about #cdej degrees ,fahrenheit4 ,electricians have therefore forsaken metals1 and fallen back on carbon for producing a light4 ,in #ahde ,mr4 ,staite devised an incandescent lamp consisting of a fine rod or stick of carbon rendered white-hot by the current1 and to preserve the carbon from burning in the atmosphere1 he enclosed it in a glass bulb1 from which the air was exhausted by an air pump4 ,edison and ,swan1 in #ahgh1 and subsequently1 went a step further1 and substituted a filament or fine thread of carbon for the rod4 ,the new lamp united the advantages of wire in point of form with those of carbon as a material4 ,the ,edison filament was made by cutting thin slips of bamboo and charring them1 the ,swan by carbonising linen fibre with sulphuric acid4 ,it was subsequently found that a hard skin could be given to the filament by flashing it--that is to say1 heating it to incandescence by the current in an atmosphere of hydrocarbon gas4 ,the filament thus treated becomes dense and resilient4 ,figure #fc represents an ordinary glow lamp of the ,edison-,swan type1 where ,e is the filament1 moulded into a loop1 and cemented to two platinum wires or electrodes ,p penetrating the glass bulb ,l1 which is exhausted of air4 ,platinum is chosen because it expands and contracts with temperature about the same as glass1 and hence there is little chance of the glass cracking through unequal stress4 ,the vacuum in the bulb is made by a mercurial air pump of the ,sprengel sort1 and the pressure of air in it is only about one-millionth of an atmosphere4 ,the bulb is fastened with a holder like that shown in figure #fd1 where two little hooks ,h connected to screw terminals ,t ,t are provided to make contact with the platinum terminals of the lamp 7,p1 figure #fc71 and the spiral spring1 by pressing on the bulb1 ensures a good contact4 ,fig4 #fe is a cut of the ordinary ,edison lamp and socket4 ,one end of the filament is connected to the metal screw ferule at the base4 ,the other end is attached to the metal button in the centre of the extreme bottom of the base4 ,screwing the lamp into the socket automatically connects the filament on one end to the screw1 on the other to an insulated plate at the bottom of the socket4 ,the resistance of such a filament hot is about #bjj ohms1 and to produce a good light from it the battery or dynamo ought to give an electromotive force of at least #ajj volts4 ,few voltaic cells or accumulators have an electromotive force of more than #b volts1 therefore we require a battery of #ej cells joined in series1 each cell giving #b volts1 and the whole set #ajj volts4 ,the strength of current in the circuit must also be taken into account4 ,to yield a good light such a lamp requires or takes about #a_/b an ampere4 ,hence the cells must be chosen with regard to their size and internal resistance as well as to their kind1 so that when the battery1 in series1 is connected to the lamp1 the resistance of the whole circuit1 including the filament or lamp1 the battery itself1 and the connecting wires shall give by ,ohm's law a current of #ab an ampere4 ,it will be understood that the current has the same strength in every part of the circuit1 no matter how it is made up4 ,thus1 if #a_/b of an ampere is flowing in the lamp1 it is also flowing in the battery and wires4 ,an ,edison-,swan lamp of this model gives a light of about #ae candles1 and is well adapted for illuminating the interior of houses4 ,the temperature of the carbon filament is about #cdej degrees ,fahr--that is to say1 the temperature at which platinum melts4 ,similar lamps of various sizes and shapes are also made1 some equivalent to as many as #ajj candles1 and fitted for large halls or streets1 others emitting a tiny beam like the spark of a glow-worm1 and designed for medical examinations1 or lighting flowers1 jewels1 and dresses in theatres or ball-rooms4 ,the electric incandescent lamp is pure and healthy1 since it neither burns nor pollutes the air4 ,it is also cool and safe1 for it produces little heat1 and cannot ignite any inflammable stuffs near it4 ,hence its peculiar merit as a light for colliers working in fiery mines4 ,independent of air1 it acts equally well under water1 and is therefore used by divers4 ,moreover1 it can be fixed wherever a wire can be run1 does not tarnish gilding1 and lends itself to the most artistic decoration4 ,electric lamps are usually connected in circuit on the series1 parallel1 and three wire system4 ,the series system is shown in figure #ff1 where the lamps ,l ,l follow each other in a row like beads on a string4 ,it is commonly reserved for the arc lamp1 which has a resistance so low that a moderate electromotive force can overcome the added resistance of the lamps1 but1 of course1 if the circuit breaks at any point all the lamps go out4 ,the parallel system is illustrated in figure #fg1 where the lamps are connected between two main conductors cross-wise1 like the steps of a ladder4 ,the current is thus divided into cross channels1 like water used for irrigating fields1 and it is obvious that1 although the circuit is broken at one point1 say by the rupture of a filament1 all the lamps do not go out4 ,fig4 #fh exhibits the ,edison three-wire system1 in which two batteries or dynamos are connected together in series1 and a third or central main conductor is run from their middle poles4 ,the plan saves a return wire1 for if two generators had been used separately1 four mains would have been necessary4 ,the parallel and three-wire systems in various groups1 with or without accumulators as local reservoirs1 are chiefly employed for incandescent lamps4 ,the main conductors conveying the current from the dynamos are commonly of stout copper insulated with air like telegraph wires1 or cables coated with india-rubber or gutta-percha1 and buried underground or suspended overhead4 ,the branch and lamp conductors or leads are finer wires of copper1 insulated with india-rubber or silk4 ,the current of an installation or section of one is made and broken at will by means of a switch or key turned by hand4 ,it is simply a series of metal contacts insulated from each other and connected to the conductors1 with a sliding contact connected to the dynamo which travels over them4 ,to guard against an excess of current on the lamps1 cut-outs1 or safety-fuses1 are inserted between the switch and the conductors1 or at other leading points in the circuit4 ,they are usually made of short slips of metal foil or wire1 which melt or deflagrate when the current is too strong1 and thus interrupt the circuit4 ,there is some prospect of the luminosity excited in a vacuum tube by the alternating currents from a dynamo or an induction coil becoming an illuminant4 ,crookes has obtained exquisitely beautiful glows by the phosphorescence of gems and other minerals in a vacuum bulb like that shown in figure #fi1 where ,a and ,b are the metal electrodes on the outside of the glass4 ,a heap of diamonds from various countries emit red1 orange1 yellow1 green1 and blue rays4 ,ruby1 sapphire1 and emerald give a deep red1 crimson1 or lilac phosphorescence1 and sulphate of zinc a magnificent green glow4 ,tesla has also shown that vacuum bulbs can be lit inside without any outside connection with the current1 by means of an apparatus like that shown in figure #gj1 where ,d is an alternating dynamo1 ,c a condenser1 ,p ,s the primary and secondary coils of a sparking transformer1 ,t ,t two metal sheets or plates1 and ,,sb the exhausted bulbs4 ,the alternating or see-saw current in this case charges the condenser and excites the primary coil ,p1 while the induced current in the secondary coil #e charges the terminal plates ,t ,t4 ,so long as the bulbs or tubes are kept within the space between the plates1 they are filled with a soft radiance1 and it is easy to see that if these plates covered the opposite walls of a room1 the vacuum lamps would yield a light in any part of it4 ,electric heating bids fair to become almost as important as electric illumination4 ,when the arc was first discovered it was noticed that platinum1 gold1 quartz1 ruby1 and diamond--in fine1 the most refractory minerals--were melted in it1 and ran like wax4 ,ores and salts of the metals were also vapourised1 and it was clear that a powerful engine of research had been placed in the hands of the chemist4 ,as a matter of fact1 the temperature of the carbons in the arc is comparable to that of the ,sun4 ,it measures #ejjj to #aj1jjj degrees ,fahrenheit1 and is the highest artificial heat known4 ,sir ,william ,siemens was among the first to make an electric furnace heated by the arc1 which fused and vapourised metallic ores1 so that the metal could be extracted from them4 ,aluminium1 chromium1 and other valuable metals are now smelted by its means1 and rough brilliants such as those found in diamond mines and meteoric stones have been crystallised from the fumes of carbon1 like hoar frost in a cold mist4 ,the electric arc is also applied to the welding of wires1 boiler plates1 rails1 and other metal work1 by heating the parts to be joined and fusing them together4 ,cooking and heating by electricity are coming more and more into favour1 owing to their cleanliness and convenience4 ,kitchen ranges1 including ovens and grills1 entirely heated by the electric current1 are finding their way into the best houses and hotels4 ,most of these are based on the principle of incandescence1 the current heating a fine wire or other conductor of high resistance in passing through it4 ,figure #ga represents an electric kettle of this sort1 which requires no outside fire to boil it1 since the current flows through fine wires of platinum or some highly resisting metal embedded in fireproof insulating cement in its bottom4 ,figures #gb and #gc are a sauce-pan and a flat-iron heated in the same way4 ,figure #gd is a cigar-lighter for smoking rooms1 the fusee ,f consisting of short platinum wires1 which become red-hot when it is unhooked1 and at the same time the lamp ,z is automatically lit4 ,figure #ge is an electric radiator for heating rooms and passages1 after the manner of stoves and hot water pipes4 ,quilts for beds1 warmed by fine wires inside1 have also been brought out1 a constant temperature being maintained by a simple regulator1 and it is not unlikely that personal clothing of the kind will soon be at the service of invalids and chilly mortals1 more especially to make them comfortable on their travels4 ,an ingenious device places an electric heater inside a hot water bag1 thus keeping it at a uniform temperature for sick-room and hospital use4 ,,chapter ,,viii4 ,,electric ,,power4 ,on the discovery of electromagnetism 7,chap4 ,,iv471 ,faraday1 ,barlow1 and others devised experimental apparatus for producing rotary motion from the electric current1 and in #ahca1 ,joseph ,henry1 the famous ,american electrician1 invented a small electromagnetic engine or motor4 ,these early machines were actuated by the current from a voltaic battery1 but in the middle of the century ,jacobi found that a dynamo-electric generator can also work as a motor1 and that by coupling two dynamos in circuit--one as a generator1 the other as a motor--it was possible to transmit mechanical power to any distance by means of electricity4 ,figure #gf is a diagram of a simple circuit for the transmission of power1 where ,d is the technical symbol for a dynamo as a generator1 having its poles 7 and -7 connected by wire to the poles of ,m1 the distant dynamo1 as a motor4 ,the generator ,d is driven by mechanical energy from any convenient source1 and transforms it into electric energy1 which flows through the circuit in the direction of the arrows1 and1 in traversing the motor ,m1 is re-transformed into mechanical energy4 ,there is1 of course1 a certain waste of energy in the process1 but with good machines and conductors1 it is not more than #aj to #be per cent41 or the efficiency of the installation is from #ge to #ij per cent--that is to say1 for every #ajj horse-power put into the generator1 from #ge to #ij horse-power are given out again by the motor4 ,it was not until #ahgj1 when ,gramme had improved the dynamo1 that power was practically transmitted in this way1 and applied to pumping water1 and other work4 ,since then great progress has been made1 and electricity is now recognised1 not only as a rival of steam1 but as the best means of distributing steam1 wind1 water1 or any other power to a distance1 and bringing it to bear on the proper point4 ,the first electric railway1 or1 rather1 tramway1 was built by ,dr4 ,werner von ,siemens at ,berlin in #ahgi1 and was soon followed by many others4 ,the wheels of the car were driven by an electric motor drawing its electricity from the rails1 which were insulated from the ground1 and being connected to the generator1 served as conductors4 ,it was found very difficult to insulate the rails1 and keep the electricity from leaking to the ground1 however1 and at the ,pans ,electrical ,exhibition of #ahha1 von ,siemens made a short tramway in which the current was drawn from a bare copper conductor running on poles1 like a telegraph wire1 along the line4 ,the system will be understood from figure #gg1 where ,l is the overhead conductor joined to the positive pole of the dynamo or generator in the power house1 and ,c is a rolling contact or trolley wheel travelling with the car and connected by the wire ,w to an electric motor ,m under the car1 and geared to the axles4 ,after passing through the motor the current escapes to the rail ,r by a brush or sliding contact ,c'1 and so returns to the negative pole of the generator4 ,a very general way is to allow the return current to escape to the rails through the wheels4 ,many tramways1 covering thousands of miles1 are now worked on this plan in the ,united ,states4 ,at ,bangor1 ,maine1 a modification of it is in use whereby the conductor is divided into sections1 alternately connected to the positive and negative poles of two generators1 coupled together as in the three-wire system of electric lighting 7page #aai71 their middle poles being joined to the earth --that is to say1 the rails4 ,it enables two cars to be run on the same line at once1 and with a considerable saving of copper4 ,to make the car independent of the conductor ,l for a short time1 as in switching1 a battery of accumulators ,b may be added and charged from the conductor1 so that when the motor is disconnected from the conductor1 the discharge from the accumulator may still work it and drive the wheels4 ,attempts have been made to run tramcars with the electricity supplied by accumulators alone1 but the system is not economical owing to the dead weight of the cells1 and the periodical trouble of recharging them at the generating station4 ,on heavy railroads worked by electricity the overhead conductor is replaced by a third rail along the middle of the track1 and insulated from the ground ,in another system the middle conductor is buried underground1 and the current is tapped at intervals by the motor connecting with it for a moment by means of spring contacts as the car travels ,in each case1 however1 the outer rails serve as the return conductors ,another system puts one or both the conductors in a conduit underground1 the trolley pole entering through a narrow slot similar to that used on cable roads ,the first electric carriages for ordinary roads were constructed in #ahhi by ,mr4 ,magnus ,volk of ,brighton4 ,figure #gh represents one of these made for the ,sultan of ,turkey1 and propelled by a one- horse-power ,immisch electric motor1 geared to one of the hind wheels by means of a chain4 ,the current for the motor was supplied by thirty ,,eps accumulators stowed in the body of the vehicle1 and of sufficient power to give a speed of ten miles an hour4 ,the driver steers with a hand lever as shown1 and controls the speed by a switch in front of him4 ,vans1 bath chairs1 and tricycles are also driven by electric motors1 but the weight of the battery is a drawback to their use4 ,in or about the year #ahci1 ,jacobi sailed an electric boat on the ,neva1 with the help of an electromagnetic engine of one horse- power1 fed by the current from a battery of ,grove cells1 and in #ahhb a screw launch1 carrying several passengers1 and propelled by an electric motor of three horse-power1 worked by forty-five accumulators1 was tried on the ,thames4 ,being silent and smokeless in its action1 the electric boat soon came into favour1 and there is now quite a flotilla on the river1 with power stations for charging the accumulators at various points along the banks4 ,figure #gi illustrates the interior of a handsome electric launch1 the ,lady ,cooper1 built for the ,e ,p ,s1 or ,electric ,power ,storage ,company4 ,an electric motor in the after part of the hull is coupled directly to the shaft of the screw propeller1 and fed by ,e ,p ,s accumulators in teak boxes lodged under the deck amidships4 ,the screw is controlled by a switch1 and the rudder by an ordinary helm4 ,the cabin is seven feet long1 and lighted by electric lamps4 ,alarm signals are given by an electric gong1 and a search-light can be brought into operation whenever it is desirable4 ,the speed attained by the ,lady ,cooper is from ten to fifteen knots4 ,m4 ,goubet1 a ,frenchman1 has constructed a submarine boat for discharging torpedoes and exploring the sea bottom1 which is propelled by a screw and an electric motor fed by accumulators4 ,it can travel entirely under water1 below the agitation of the waves1 where sea-sickness is impossible1 and the inventor hopes that vessels of the kind will yet carry passengers across the ,channel4 ,the screw propeller of the ,edison and ,sim's torpedo is also driven by an electric motor4 ,in this case the current is conveyed from the ship or fort which discharges the torpedo by an insulated conductor running off a reel carried by the torpedo1 the earth or return half of the circuit being the sea-water4 ,all sorts of machinery are now worked by the electric motor--for instance1 cranes1 elevators1 capstans1 rivetters1 lathes1 pumps1 chaff-cutters1 and saws4 ,of domestic appliances1 figure #hj shows an air propeller or ventilation fan1 where ,f is a screw-like fan attached to the spindle of the motor ,m1 and revolving with its armature4 ,figure #ha represents a ,trouve motor working a sewing- machine1 where ,n is the motor which gears with ,p the driving axle of the machine4 ,figure #hb represents a fine drill actuated by a ,griscom motor4 ,the motor ,m is suspended from a bracket ,a ,b ,c by the tackle ,d ,e1 and transmits the rotation of its armature by a flexible shaft ,s ,t to the terminal drill ,o1 which can be applied at any point1 and is useful in boring teeth4 ,now that electricity is manufactured and distributed in towns and villages for the electric light1 it is more and more employed for driving the lighter machinery4 ,steam1 however1 is more economical on a large scale1 and still continues to be used in great factories for the heavier machinery4 ,nevertheless a day is coming when coal1 instead of being carried by rail to distant works and cities1 will be burned at the pit mouth1 and its heat transformed by means of engines and dynamos into electricity for distribution to the surrounding country4 ,i have shown elsewhere that peat can be utilised in a similar manner1 and how the great ,bog of ,allen is virtually a neglected gold field in the heart of ,ireland4 ,footnote3 ,the ,nineteenth ,century for ,december #ahid4 ,the sunshine of deserts1 and perhaps the electricity of the atmosphere1 but at all events the power of winds1 waves1 and waterfalls are also destined to whirl the dynamo1 and yield us light1 heat1 or motion4 ,much has already been done in this direction4 ,in #ahia the power of turbines driven by the ,falls of ,neckar at ,lauffen was transformed into electricity1 and transmitted by a small wire to the ,electrical ,exhibition of ,frankfort-on-the-,main1 #aag miles away4 ,the city of ,rome is now lighted from the ,falls of ,tivoli1 #af miles distant4 ,the finest cataract in ,great ,britain1 the ,falls of ,foyers1 in the ,highlands1 which persons of taste and culture wished to preserve for the nation1 is being sacrificed to the spirit of trade1 and deprived of its waters for the purpose of generating electricity to reduce aluminium from its ores4 ,the great scheme recently completed for utilizing the power of ,niagara ,falls by means of electricity is a triumph of human enterprise which outrivals some of the bold creations of ,jules ,verne4 ,when in #afgh the ,french missionaries ,la ,salle and ,hennepin discovered the stupendous cataract on the ,niagara ,river between ,lake ,ontario and ,lake ,erie1 the science of electricity was in its early infancy1 and little more was known about the mysterious force which is performing miracles in our day than its manifestation on rubbed amber1 sealing-wax1 glass1 and other bodies4 ,nearly a hundred years had still to pass ere ,franklin should demonstrate the identity of the electric fire with lightning1 and nearly another hundred before ,faraday should reveal a mode of generating it from mechanical power4 ,assuredly1 neither ,la ,salle nor his contemporaries ever dreamed of a time when the water-power of the ,falls would be distributed by means of electricity to produce light or heat and serve all manner of industries in the surrounding district4 ,the awestruck ,iroquois ,indians had named the cataract ,oniagahra1 or ,thunder of the ,waters1 and believed it the dwelling-place of the ,spirit of ,thunder4 ,this poetical name is none the less appropriate now that the modern electrician is preparing to draw his lightnings from its waters and compel the genius loci to become his willing bondsman4 ,the ,falls of ,niagara are situated about twenty-one miles from ,lake ,erie1 and fourteen miles from ,lake ,ontario4 ,at this point the ,niagara ,river1 nearly a mile broad1 flowing between level banks1 and parted by several islands1 is suddenly shot over a precipice #agj feet high1 and making a sharp bend to the north1 pursues its course through a narrow gorge towards ,lake ,ontario4 ,the ,falls are divided at the brink by ,goat ,island1 whose primeval woods are still thriving in their spray4 ,the ,horseshoe ,fall on the ,canadian side is #hab yards1 and the ,american ,falls on the south side are #cbe yards wide4 ,for a considerable distance both above and below the ,falls the river is turbulent with rapids4 ,the water-power of the cataract has been employed from olden times4 ,the ,french fur-traders placed a mill beside the upper rapids1 and the early ,british settlers built another to saw the timher used in their stockades4 ,by-and-by1 the ,stedman and ,porter mills were established below the ,falls2 and subsequently1 others which derived their water-supply from the lower rapids by means of raceways or leads4 ,eventually1 an open hydraulic canal1 three- fourths of a mile long1 was cut across the elbow of land on the ,american side1 through the town of ,niagara ,falls1 between the rapids above and the verge of the chasm below the ,falls1 where1 since #ahgd1 a cluster of factories has arisen1 which discharge their spent water over the cliff in a series of cascades almost rivalling ,niagara itself4 ,this canal1 which only taps a mere drop from the ocean of power that is running to waste1 has been utilised to the full2 and the decrease of water-privileges in the ,new ,england ,states1 owing to the clearing of the forests and settlement of the country1 together with the growth of the electrical industries1 have led to a further demand on the resources of ,niagara4 ,with the example of ,minneapolis1 which draws the power for its many mills from the ,falls of ,st4 ,anthony1 in the ,mississippi ,river1 before them1 a group of far-seeing and enterprising citizens of ,niagara ,falls resolved to satisfy this requirement by the foundation of an industrial city in the neighbourhood of the ,falls4 ,they perceived that a better site could nowhere be found on the ,american ,continent4 ,apart from its healthy air and attractive scenery1 ,niagara is a kind of half-way house between the ,east and ,west1 the consuming and the producing ,states4 ,by the ,erie ,canal at ,tonawanda it commands the great waterway of the ,lakes and the ,st4 ,lawrence4 ,a system of trunk railways from different parts of the ,states and ,canada are focussed there1 and cross the river by the ,cantilever and ,suspension bridges below the ,falls4 ,the ,new ,york ,central and ,hudson ,river1 the ,lehigh ,valley1 the ,buffalo1 ,rochester1 and ,pittsburgh1 the ,michigan ,central1 and the ,grand ,trunk of ,canada1 are some of these lines4 ,draining as it does the great lakes of the interior1 which have a total area of #ib1jjj square miles1 with an aggregate basin of #bij1jjj square miles1 the volume of water in the ,niagara ,river passing over the cataract every second is something like #cjj1jjj cubic feet2 and this1 with a fall of #bgf feet from the head of the upper rapids to the whirlpool rapids below1 is equivalent to about nine million1 or1 allowing for waste in the turbines1 say1 seven million horse- power4 ,moreover1 the great lakes discharging--into each other form a chain of immense reservoirs1 and the level of the river being little affected by flood or drought1 the supply of pure water is practically constant all the year round4 ,mr4 ,r4 ,c4 ,reid has shown that a rainfall of three inches in twenty-four hours over the basin of ,lake ,superior would take ninety days to run off into ,lake ,huron1 which1 with ,lake ,michigan1 would take as long to overflow into ,lake ,erie2 and1 therefore1 six months would elapse before the full effect of the flood was expended at the ,falls4 ,the first outcome of the movement was the ,niagara ,river ,hydraulic ,power and ,sewer ,company1 incorporated in #ahhf1 and succeeded by the ,niagara ,falls ,power ,company4 ,the old plan of utilising the water by means of an open canal was unsuited to the circumstances1 and the company adopted that of the late ,mr4 ,thomas ,evershed1 divisional engineer of the ,new ,york ,state ,canals4 ,like the other1 it consists in tapping the river above the ,falls1 and using the pressure of the water to drive the number of turbines1 then restoring the water to the river below the ,falls2 but instead of a surface canal1 the tail-race is a hydraulic tunnel or underground conduit4 ,to this end some fifteen hundred acres of spare land1 having a frontage just above the upper rapids1 was quietly secured at the low price of three hundred dollars an acre2 and we believe its rise in value owing to the progress of the works is such that a yearly rental of two hundred dollars an acre can even now be got for it4 ,this land has been laid out as an industrial city1 with a residential quarter for the operatives1 wharves along the river1 and sidings or short lines to connect with the trunk railways4 ,in carrying out their purpose the company has budded and branched into other companies--one for the purchase of the land2 another for making the railways2 and a third1 the ,cataract ,construction ,company1 which is charged with the carrying out of the engineering works1 for the utilisation of the water-power1 and is therefore the most important of all4 ,a subsidiary company has also been formed to transmit by electricity a portion of the available power to the city of ,buffalo1 at the head of the ,niagara ,river1 on ,lake ,erie1 some twenty miles distant4 ,all these affiliated bodies are1 however1 under the directorate of the ,cataract ,construction ,company2 and amongst those who have taken the most active part in the work we may mention the president1 ,mr4 ,e4 ,d4 ,adams2 ,professor ,coleman ,sellers1 the consulting engineer2 and ,professor ,george ,forbes1 ,f4 ,r4 ,s41 the consulting electrical engineer1 a son of the late ,principal ,forbes of ,edinburgh4 ,in securing the necessary right of way for the hydraulic tunnel or in the acquisitom of land1 the ,company has shown consummate tact4 ,a few proprietors declined to accept its terms1 and the ,company selected a parallel route4 ,having obtained the right of way for the latter1 it informed the refractory owners on the first line of their success1 and intimated that the ,company could now dispense with that4 ,on this the sticklers professed their willingness to accept the original terms1 and the bargain was concluded1 thus leaving the ,company in possession of the rights of way for two tunnels1 both of which they propose to utilise4 ,the liberal policy of the directors is deserving of the highest commendation4 ,they have risen above mere chauvinism1 and instead of narrowly confining the work to ,american engineers1 they have availed themselves of the best scientific counsel which the entire world could afford4 ,the great question as to the best means of distributing and applying the power at their command had to be settled2 and in #ahij1 after ,mr4 ,adams and ,dr4 ,sellers had made a visit of inspection to ,europe1 an ,international ,commission was appointed to consider the various methods submitted to them1 and award prizes to the successful competitors4 ,lord ,kelvin 7then ,sir ,william ,thomson7 was the president1 and ,professor ,w4 ,c4 ,unwin1 the well-known expert in hydraulic engineering1 the secretary1 while other members were ,professor ,mascart of the ,institute1 a leading ,french electrician2 ,colonel ,turretini of ,geneva1 and ,dr4 ,sellers4 ,a large number of schemes were sent in1 and many distinguished engineers gave evidence before the ,commission4 ,the relative merits of compressed air and electricity as a means of distributing the power were discussed1 and on the whole the balance of opinion was in favour of electricity4 ,prizes of two hundred and two hundred and fifty pounds were awarded to a number of firms who had submitted plans1 but none of these were taken up by the ,company4 ,the impulse turbines of ,messrs4 ,faesch ,piccard1 of ,geneva1 who gained a prize of two hundred and fifty pounds1 have1 however1 been adopted since4 ,it is another proof of the determination of the ,company to procure the best information on the subject1 regardless of cost1 that ,professor ,forbes had carte blanche to go to any part of the world and make a report on any system of electrical distribution which he might think fit4 ,with the selection of electricity another question arose as to the expediency of employing continuous or alternating currents4 ,at that time continuous currents were chiefly in vogue1 and it speaks well for the sagacity and prescience of ,professor ,forbes that he boldly advocated the adoption of alternating currents1 more especially for the transmission of power to ,buffalo4 ,his proposals encountered strong opposition1 even in the highest quarters2 but since then1 partly owing to the striking success of the ,lauffen to ,frankfort experiment in transmitting power by alternating currents over a bare wire on poles a distance of more than a hundred miles1 the directors and engineers have come round to his view of the matter1 and alternating currents have been employed1 at all events for the ,buffalo line1 and also for the chief supply of the industrial city4 ,continuous currents1 flowing always in the same direction1 like the current of a battery1 can1 it is true1 be stored in accumulators1 but they cannot be converted to higher or lower pressure in a transformer4 ,alternating currents1 on the other hand1 which see-saw in direction many times a second1 cannot be stored in accumulators1 but they can be sent at high pressure along a very fine wire1 and then converted to higher or lower pressures where they are wanted1 and even to continuous currents4 ,each kind1 therefore1 has its peculiar advantages1 and both will be employed to some extent4 ,with regard to the engineering works1 the hydraulic tunnel starts from the bank of the river where it is navigable1 at a point a mile and a half above the ,falls1 and after keeping by the shore1 it cuts across the bend beneath the city of ,niagara ,falls1 and terminates below the ,suspension ,bridge under the ,falls at the level of the water4 ,it is #fgjj yards long1 and of a horseshoe section1 #ai feet wide by #ba feet high4 ,it has been cut #afj feet below the surface through the limestone and shale1 but is arched with brick1 having rubble above1 and at the outfall is lined on the invert or under side with iron4 ,the gradient is #cf feet in the mile1 and the total fall is #bje feet1 of which #adj feet are available for use4 ,the capacity of the tunnel is #ajj1jjj horse- power4 ,in the lands of the company it is #djj feet from the margin of the river1 to which it is connected by a canal1 which is over #aejj feet long1 #ejj feet wide at the mouth1 and #ab feet deep4 ,out of this canal1 head-races fitted with sluices conduct the water to a number of wheel-pits #afj feet deep1 which have been dug near the edge of the canal1 and communicate below with the tunnel4 ,at the bottom of each wheel-pit a #ejjj horse-power ,girard double turbine is mounted on a vertical shaft1 which drives a propeller shaft rising to the surface of the ground2 a dynamo of #ejjj horse- power is fixed on the top of this shaft1 and so driven by it4 ,the upward pressure of the water is ingeniously contrived to relieve the foundation of the weight of the turbine shaft and dynamo4 ,twenty of these turbines1 which are made by the ,i4 ,p4 ,morris ,company of ,philadelphia1 from the designs of ,messrs4 ,faesch and ,piccard1 will be required to utilize the full capacity of the tunnel4 ,the company possesses a strip of land extending two miles along the shore2 and in excavating the tunnel a coffer-dam was made with the extracted rock1 to keep the river from flooding the works4 ,this dam now forms part of a system by which a tract of land has been reclaimed from the river4 ,part of it has already been acquired by the ,niagara ,paper ,pulp ,company1 which is building gigantic factories1 and will employ the tailrace or tunnel of the ,cataract ,construction ,company4 ,wharfs for the use of ships and canal boats will also be constructed on this frontage4 ,by land and water the raw materials of the ,west will be conveyed to the industrial town which is now coming into existence2 grain from the prairies of ,illinois and ,dakota2 timber from the forests of ,michigan and ,wisconsin2 coal and copper from the mines of ,lake ,superior2 and what not4 ,it is expected that one industry having a seat there will attract others4 ,thus1 the pulp mills will bring the makers of paper wheels and barrels2 the smelting of iron will draw foundries and engine works2 the electrical refining of copper will lead to the establishment of wire-works1 cable factories1 dynamo shops1 and so on4 ,aluminum1 too1 promises to create an important industry in the future4 ,in the meantime1 the ,cataract ,construction ,company is about to start an electrical factory of its own1 which will give employment to a large number of men4 ,it has also undertaken the water supply of the adjacent city of ,niagara ,falls4 ,the ,cataract ,electric ,company of ,buffalo has obtained the exclusive right to use the electricity transmitted to that city1 and the line will be run in a subway4 ,this underground line will be more expensive to make than an overhead line1 but it will not require to be renewed every eight to fifteen years1 and it will not be liable to interruption from the heavy gales that sweep across the lakes1 or the weight of frozen sleet3 moreover1 it will be more easily inspected1 and quite safe for the public4 ,we should also add that1 in addition to the contemplated duplicate tunnel of #ajj1jjj horse-power1 the ,cataract ,construction ,company owns a concession for utilising #bej1jjj horse-power from the ,horseshoe ,falls on the ,canadian side in the same manner4 ,it has thus a virtual monopoly of the available water-power of ,niagara1 and the promoters have not the least doubt that the enterprise will be a great financial success4 ,already the ,pittsburg ,reduction ,company have begun to use the electricity in reducing aluminum from the mineral known as bauxite1 an oxide of the metal1 by means of the electric furnace4 ,another portion of the power is to be used to produce carbide of calcium for the manufacture of acetylene gas4 ,at a recent electrical exhibition held in ,new ,york city a model of the ,niagara plant was operated by an electric current brought from ,niagara1 #dej miles distant2 and a collection of telephones were so connected that the spectator could hear the roar of the real cataract4 ,thanks to the foresight of ,new ,york ,state and ,canada1 the scenery of the ,falls has been preserved by the institution of public parks1 and the works in question will do nothing to spoil it1 especially as they will be free from smoke4 ,mr4 ,bogarts1 ,state ,engineer of ,new ,york1 estimates that the water drawn from the river will only lower the mean depth of the ,falls about two inches1 and will therefore make no appreciable difference in the view4 ,altogether1 the enterprise is something new in the history of the world4 ,it is not only the grandest application of electrical power1 but one of the most remarkable feats in an age when romance has become science1 and science has become romance4 ,,chapter ,,ix4 ,,minor ,,uses ,,of ,,electricity4 ,the electric trembling bell1 now in common use1 was first invented by ,john ,mirand in #ahej4 ,figure #hc shows the scheme of the circuit1 where ,b is a small battery1 say two or three dry or ,leclanche cells1 joined by insulated wire to ,p1 a press-button or contact key1 and ,g an electromagnetic gong or bell4 ,on pressing the button ,p1 a spring contact is made1 and the current flowing through the circuit strikes the bell4 ,the action of the contact key will be understood from figure #hd1 where ,p is the press-button removed to show the underlying mechanism1 which is merely a metal spring ,a over a metal plate ,b4 ,the spring is connected by wire to a pole of the battery1 and the plate to a terminal or binding screw of the bell1 or vice versa4 ,when the button ,p is pressed by the finger the spring is forced against the plate1 the circuit is made1 and the bell rings4 ,on releasing the button it springs back1 the circuit is broken1 and the bell stops4 ,figure #he shows the inner mechanism of the bell1 which consists of a double-poled electromagnet ,m1 having a soft iron armature ,a hinged on a straight spring or tongue ,s1 with one end fixed1 and the other resting against a screw contact ,t4 ,the hammer ,h projects from the armature beside the edge of the gong ,e4 ,in passing through the instrument the current proceeds from one terminal1 say that on the right1 by the wire ,w to the screw contact ,t1 and thence by the spring ,s through the bobbins of the electromagnet to the other terminal4 ,the electromagnet attracts the armature ,a1 and the hammer ,h strikes the gong2 but in the act the spring ,s is drawn from the contact ,t1 and the circuit is broken4 ,consequently the electromagnet1 no longer excited1 lets the armature go1 and the spring leaps back against the contact ,t1 withdrawing the hammer from the gong4 ,but the instrument is now as it was at first1 the current again flows1 and the hammer strikes the gong1 only to fly back a second time4 ,in this way1 as long as the button is pressed by the operator1 the hammer will continue to tap the bell and give a ringing sound4 ,press-buttons are of various patterns1 and either affixed to the wall or inserted in the handle of an ordinary bell-pull1 as shown in figure #hf4 ,the ordinary electric bell actuated by a battery is liable to get out of order owing to the battery spending its force1 or to the contacts becoming dirty4 ,magnetoelectric bells have1 therefore1 been introduced of late years4 ,with these no battery or interrupting contacts are required1 since the bell-pull or press- button is made in the form of a small dynamo which generates the current when it is pulled or pushed4 ,figure #hg illustrates a form of this apparatus1 where ,m ,p is the bell-pull and ,b the bell1 these being connected by a double wire ,w1 to convey the current4 ,the bell-pull consists of a horseshoe magnet ,m1 having a bobbin of insulated wire between its poles1 and mounted on a spindle4 ,when the key ,p is turned round by the hand1 the bobbin moves in the magnetic field between the poles of the magnet1 and the current thus generated circulates in the wires ,w1 and passing through an electromagnet under the bell1 attracts its armature1 and strikes the hammer on the bell4 ,of course the bell may be placed at any distance from the generator4 ,in other types the current is generated and the bell rung by the act of pulling1 as in a common house-bell4 ,electric bells in large houses and hotels are usually fitted up with indicators1 as shown in figure #hh1 which tell the room from which the call proceeds4 ,they are serviceable as instantaneous signals1 annunciators1 and alarms in many different ways4 ,an outbreak of fire can be announced by causing the undue rise of temperature to melt a piece of tallow or fusible metal1 and thus release a weight1 which tails on a press-button1 and closes the circuit of an electric bell4 ,or1 the rising temperature may expand the mercury in a tube like that of a thermometer until it connects two platinum wires fused through the glass and in circuit with a bell4 ,some employ a curving bi-metallic spring to make the necessary contact4 ,the spring is made by soldering strips of brass and iron back to back1 and as these metals expand unequally when heated1 the spring is deformed1 and touches the contact which is connected in the circuit1 thus permitting the current to ring the bell4 ,a still better device1 however1 is a small box containing a thin metallic diaphragm1 which expands with the heat1 and sagging in the centre1 touches a contact screw1 thus completing the circuit1 and allowing the current to pass4 ,these automatic or self-acting fire-alarms can1 of course1 be connected in the circuit of the ordinary street fire-alarms1 which are usually worked by pulling a handle to make the necessary contact4 ,from what has been said1 it will be easy to understand how the stealthy entrance of burglars into a house can be announced by an electric bell or warning lamp4 ,if press-buttons or contact-keys are placed on the sashes of the windows1 the posts of the door1 or the treads of the stair1 so that when the window or door is opened1 or the tread bends under the footstep1 an electric circuit is closed1 the alarm will be given4 ,of course1 the connections need only be arranged when the device is wanted4 ,shops and offices can be guarded by making the current show a red light from a lamp hung in front of the premises1 so that the night watchman can see it on his beat4 ,this can readily be done by adjusting an electromagnet to drop a screen of red glass before the flame of the lamp4 ,safes and showcases forcibly opened can be made to signal the fact1 and recently in the ,united ,states a thief was photographed by a flashlight kindled in this way1 and afterwards captured through the likeness4 ,the level of water in cisterns and reservoirs1 can be told in a similar manner by causing a float to rise with the water and make the required contact4 ,the degree of frost in a conservatory can also be announced by means of the mercury thermostat1 already described1 or some equivalent device4 ,there are1 indeed1 many actual or possible applications of a similar kind4 ,the ,massey log is an instrument for telling the speed of a ship by the revolutions of a fly as it is towed through the water1 and by making the fly complete a circuit as it revolves the number of turns a second can be struck by a bell on board4 ,in one form of the electric log1 the current is generated by the chemical action of zinc and copper plates attached to the log1 and immersed in the sea water1 and in others provided by a battery on the ship4 ,captain ,m',evoy has invented an alarm for torpedoes and torpedo boats1 which is a veritable watchdog of the sea4 ,it consists of an iron bell-jar inverted in the water1 and moored at a depth below the agitation of the waves4 ,in the upper part of the jar1 where the pressure of the air keeps back the water1 there is a delicate needle contact in circuit with a battery and an electric bell or lamp1 as the case may be1 on the shore4 ,waves of sound passing through the water from the screw propeller of the torpedo1 or1 indeed1 any ship1 make and break the sensitive contact1 and ring the bell or light the lamp4 ,the apparatus is intended to alarm a fleet lying at anchor or a port in time of war4 ,electricity has also been employed to register the movements of weathercocks and anemometers4 ,a few years ago it was applied successfully to telegraph the course marked by a steering compass to the navigating officer on the bridge4 ,this was done without impeding the motion of the compass card by causing an electric spark to jump from a light pointer on the card to a series of metal plates round the bowl of the compass1 and actuate an electric alarm4 ,the ,domestic ,telegraph1 an ,american device1 is a little dial apparatus by which a citizen can signal for a policeman1 doctor1 messenger1 or carriage1 as well as a fire engine1 by the simple act of setting a hand on the dial4 ,alexander ,bain was the first to drive a clock with electricity instead of weights1 by employing a pendulum having an iron bob1 which was attracted to one side and the other by an electromagnet1 but as its rate depends on the constancy of the current1 which is not easy to maintain1 the invention has not come into general use4 ,the butterfly clock of ,lemoine1 which we illustrate in figure #hi1 is an improved type1 in which the bob of soft iron ,p swings to and fro over the poles of a double electro magnet ,m in circuit with a battery and contact key4 ,when the rate is too slow the key is closed1 and a current passing through the electromagnet pulls on the pendulum1 thus correcting the clock4 ,this is done by the ingenious device of ,hipp1 shown in figure #ij1 where ,m is the electromagnet1 ,p the iron bob1 from which projects a wire bearing a light vane ,b of mica in the shape of a butterfly4 ,as the bob swings the wire drags over the hump of the metal spring ,s1 and when the bob is going too slowly the wire thrusts the spring into contact with another spring ,t below1 thus closing the circuit1 and sending a current through the magnet ,m1 which attracts the bob and gives a fillip to the pendulum4 ,local clocks controlled from a standard clock by electricity have been more successful in practice1 and are employed in several towns--for example1 ,glasgow4 ,behind local dials are electromagnets which1 by means of an armature working a frame and ratchet wheel1 move the hands forward every minute or half-minute as the current is sent from the standard clock4 ,the electrical chronograph is an instrument for measuring minute intervals of time by means of a stylus tracing a line on a band of travelling paper or a revolving barrel of smoked glass4 ,the current1 by exciting an electromagnet1 jerks the stylus1 and the interval between two jerks is found from the length of the trace between them and the speed of the paper or smoked surface4 ,retarded clocks are sometimes employed as electric meters for registering the consumption of electricity4 ,in these the current to be measured flows through a coil beneath the bob of the pendulum1 which is a magnet1 and thus affects the rate4 ,in other meters the current passes through a species of galvanometer called an ampere meter1 and controls a clockwork counter4 ,in a third kind of meter the chemical effect of the current is brought into play-- that of ,edison1 for example1 decomposing sulphate of copper1 or more commonly of zinc4 ,the electric light is now used for signalling and advertising by night in a variety of ways4 ,incandescent lamps inside a translucent balloon1 and their light controlled by a current key1 as in a telegraph circuit1 so as to give long and short flashes1 according to the ,morse code1 are employed in the army4 ,signals at sea are also made by a set of red and white glow-lamps1 which are combined according to the code in use4 ,the powerful arc lamp is extremely useful as a search light1 especially on men of war and fortifications1 and it has also been tried in signalling by projecting the beam on the clouds by way of a screen1 and eclipsing it according to a given code4 ,in #ahgi1 ,professor ,graham ,bell1 the inventor of the speaking telephone1 and ,mr ,summer ,tamter1 brought out an ingenious apparatus called the photophone1 by which music and speech were sent along a beam of light for several hundred yards4 ,the action of the photophone is based on the peculiar fact observed in #ahgc by ,mr ,j ,e ,mayhew1 that the electrical resistance of crystalline selenium diminishes when a ray of light falls upon it4 ,figure #ia shows how ,bell and ,tamter utilised this property in the telephone4 ,a beam of sun or electric light1 concentrated by a lens ,l1 is reflected by a thin mirror ,m1 and after traversing another lens ,l1 travels to the parabolic reflector ,r1 in the focus of which there is a selenium resistance in circuit with a battery ,s and two telephones ,t ,t'4 ,now1 when a person speaks into the tube at the back of the mirror ,m1 the light is caused to vibrate with the sounds1 and a wavering beam falls on the selenium1 changing its resistance to the current4 ,the strength of the current is thus varied with the sonorous waves1 and the words spoken by the transmitter are heard in the telephones by the receiver4 ,the photophone is1 however1 more of a scientific toy than a practical instrument4 ,becquerel1 the ,french chemist1 found that two plates of silver freshly coated with silver from a solution of chloride of silver and plunged into water1 form a voltaic cell which is sensitive to light4 ,this can be seen by connecting the plates through a galvanometer1 and allowing a ray of light to fall upon them4 ,other combinations of the kind have been discovered1 and ,professor ,minchin1 the ,irish physicist1 has used one of these cells to measure the intensity of starlight4 ,the induction balance of ,professor ,hughes is founded on the well-known fact that a current passing in one wire can induce a sympathetic current in a neighbouring wire4 ,the arrangement will be understood from figure #ib1 where ,p and ,p#a are two similar coils or bobbins of thick wire in circuit with a battery ,b and a microphone ,m1 while ,s and ,s#a are two similar coils or bobbins of fine wire in circuit with a telephone ,t4 ,it need hardly be said that when the microphone ,m is disturbed by a sound1 the current in the primary coils ,p ,p#a will induce a corresponding current in the secondary coils ,s ,s#a2 but the coils ,s ,s#a are so wound that the induction of ,p on ,s neutralises the induction of ,p#a on ,s#a2 and no current passes in the secondary circuit1 hence no sound is heard in the telephone4 ,when1 however1 this balance of induction is upset by bringing a piece of metal--say1 a coin--near one or other of the coils ,s ,s#a1 a sound will be heard in the telephone4 ,the induction balance has been used as a ,sonometer for measuring the sense of hearing1 and also for telling base coins4 ,the writer devised a form of it for divining the presence of gold and metallic ores which has been applied by ,captain ,m',evoy in his submarine detector for exploring the sea bottom for lost anchors and sunken treasure4 ,when ,president ,garfield was shot1 the position of the bullet was ascertained by a similar arrangement4 ,the microphone as a means of magnifying feeble sounds has been employed for localising the leaks in water pipes and in medical examinations4 ,some years ago it saved a ,russian lady from premature burial by rendering the faint beating of her heart audible4 ,edison's electric pen is useful in copying letters4 ,it works by puncturing a row of minute holes along the lines of the writing1 and thus producing a stencil plate1 which1 when placed over a clean sheet of paper and brushed with ink1 gives a duplicate of the writing by the ink penetrating the holes to the paper below4 ,it is illustrated in figure #ic1 where ,p is the pen1 consisting of a hollow stem in which a fine needle actuated by the armature of a small electromagnet plies rapidly up and down and pierces the paper4 ,the current is derived from a small battery ,b1 and an inking roller like that used in printing serves to apply the ink4 ,in #ahgh ,mr4 ,edison announced his invention of a machine for the storage and reproduction of speech1 and the announcement was received with a good deal of incredulity1 notwithstanding the partial success of ,faber and others in devising mechanical articulators4 ,the simplicity of ,edison's invention when it was seen and heard elicited much admiration1 and although his first instrument was obviously imperfect1 it was nevertheless regarded as the germ of something better4 ,if the words spoken into the instrument were heard in the first place1 the likeness of the reproduction was found to be unmistakable4 ,indeed1 so faithful was the replica1 that a member of the ,academy of ,sciences1 ,paris1 stoutly maintained that it was due to ventriloquism or some other trickery4 ,it was evident1 however1 that before the phonograph could become a practical instrument1 further improvements in the nicety of its articulation were required4 ,the introduction of the electric light diverted ,mr4 ,edison from the task of improving it1 although he does not seem to have lost faith in his pet invention4 ,during the next ten years he accumulated a large fortune1 and was the principal means of introducing both electric light and power to the world at large4 ,this done1 however1 he returned to his earlier love1 and has at length succeeded in perfecting it so as to redeem his past promises and fulfill his hopes regarding it4 ,the old instrument consisted1 as is well known1 of a vibrating tympan or drum1 from the centre of which projected a steel point or stylus1 in such a manner that on speaking to the tympan its vibrations would urge the stylus to dig into a sheet of tinfoil moving past its point4 ,the foil was supported on a grooved barrel1 so that the hollow of the groove behind it permitted the foil to give under the point of the stylus1 and take a corrugated or wavy surface corresponding to the vibrations of the speech4 ,thus recorded on a yielding but somewhat stiff material1 these undulations could be preserved1 and at a future time made to deflect the point of a similar stylus1 and set a corresponding diaphragm or tympan into vibration1 so as to give out the original sounds1 or an imitation of them4 ,tinfoil1 however1 is not a very satisfactory material on which to receive the vibrations in the first place4 ,it does not precisely respond to the movements of the marking stylus in taking the impression1 and does not guide the receiving stylus sufficiently well in reproducing sounds4 ,mr4 ,edison has therefore adopted wax in preference to it2 and instead of tinfoil spread on a grooved support1 he now employs a cylinder of wax to take the print of the vibrations4 ,moreover1 he no longer uses the same kind of diaphragm to print and receive the sounds1 but employs a more delicate one for receiving them4 ,the marking cylinder is now kept in motion by an electric motor1 instead of by hand-turning1 as in the earlier instrument4 ,the new phonograph1 which we illustrate in figure #id1 is about the size of an ordinary sewing machine1 and is of exquisite workmanship1 the performance depending to a great extent on the perfection and fitness of the mechanism4 ,it consists of a horizontal spindle ,s1 carrying at one end the wax cylinder ,c1 on which the sonorous vibrations are to be imprinted4 ,over the cylinder is supported a diaphragm or tympan ,t1 provided with a conical mouthpiece ,m for speaking into4 ,under the tympan there is a delicate needle or stylus1 with its point projecting from the centre of the tympan downwards to the surface of the wax cylinder1 so that when a person speaks into the mouthpiece1 the voice vibrates the tympan and drives the point of the stylus down into the wax1 making an imprint more or less deep in accordance with the vibrations of the voice4 ,the cylinder is kept revolving in a spiral path1 at a uniform speed1 by means of an electric motor ,e1 fitted with a sensitive regulator and situated at the base of the machine4 ,the result is that a delicate and ridgy trace is cut in the surface of wax along a spiral line4 ,this is the sound record1 and by substituting a finer tympan for the one used in producing it1 the ridges and inequalities of the trace can be made to agitate a light stylus resting on them1 and cause it to set the delicate tympan into vibrations corresponding very accurately to those of the original sounds4 ,the tympan employed for receiving is made of gold-beater's skin1 having a stud at its centre and a springy stylus of steel wire4 ,the sounds emitted by this device are almost a whisper as compared to the original ones1 but they are faithful in articulation1 which is the main object1 and they are conveyed to the ear by means of flexible hearing-tubes4 ,these tympans are interchangeable at will1 and the arm which carries them is also provided with a turning tool for smoothing the wax cylinder prior to its receiving the print4 ,the cylinders are made of different sizes1 from #a to #h inches long and #d inches in diameter4 ,the former has a storage capacity of #bjj words4 ,the next in size has twice that1 or #djj words1 and so on4 ,mr4 ,edison states that four of the large #h-;inch cylinders can record all ,nicholas ,nickleby1 which could therefore be automatically read to a private invalid or to a number of patients in a hospital simultaneously1 by means of a bunch of hearing-tubes4 ,the cylinders can be readily posted like letters1 and made to deliver their contents viva voce in a duplicate phonograph1 every tone and expression of the writer being rendered with more or less fidelity4 ,the phonograph has proved serviceable in recording the languages and dialects of vanishing races1 as well as in teaching pronunciation4 ,the dimensions1 form1 and consequent appearance of the present commercial ,american phonograph are quite different from that above described1 but the underlying principles and operations are identical4 ,a device for lighting gas by the electric spark is shown in figure #ie1 where ,a is a flat vulcanite box1 containing the apparatus which generates the electricity1 and a stem or pointer ,l1 which applies the spark to the gas jet4 ,the generator consists of a small influence machine1 which is started by pressing the thumb- key ,c on the side of the box4 ,the rotation of a disc inside the box produces a supply of static electricity1 which passes in a stream of sparks between two contact-points in the open end of the stem ,d4 ,the latter is tubular1 and contains a wire insulated from the metal of the tube1 and forming with the tube the circuit for the electric discharge4 ,the handle enables the contrivance to be readily applied4 ,the apparatus is one of the few successful practical applications of static electricity4 ,other electric gas-lighters consist of metal points placed on the burner1 so that the electric spark from a small induction coil or dynamo kindles the jet4 ,a platinum wire made white-hot by the passage of a current is sometimes used to light lamps1 as shown in figure #if1 where ,w is a small spiral of platinum connected in circuit with a generator by the terminals ,t ,t4 ,when the lamp ,l is pressed against the button ,b the wire glows and lights it4 ,explosives1 such as gunpowder and guncotton1 are also ignited by the electric spark from an induction coil or the incandescence of a wire4 ,figure #ig shows the interior of an ordinary electric fuse for blasting or exploding underground mines4 ,it consists of a box of wood or metal primed with gunpowder or other explosive1 and a platinum wire ,p soldered to a pair of stout copper wires ,w1 insulated with gutta-percha4 ,when the current is sent along these wires1 the platinum glows and ignites the explosive4 ,detonating fuses are primed with fulminate of mercury4 ,springs for watches and other purposes are tempered by heating them with the current and quenching them in a bath of oil4 ,electrical cautery is performed with an incandescent platinum wire in lieu of the knife1 especially for such operations as the removal of the tongue or a tumour4 ,it was known to the ancients that a fish called a torpedo existed in the ,mediterranean which was capable of administering a shock to persons and benumbing them4 ,the torpedo1 or electric ray1 is found in the ,atlantic as well as the ,mediterranean1 and is allied to the skate4 ,it has an electric organ composed of #hjj or #ajjj polygonal cells in its head1 and the discharge1 which appears to be a vibratory current1 passes from the back or positive pole to the belly or negative pole through the water4 ,the gymotus1 or ,surinam eel1 which attains a length of five or six feet1 has an electric organ from head to tail1 and can give a shock sufficient to kill a man4 ,humboldt has left a vivid picture of the frantic struggles of wild horses driven by the ,indians of ,venezuela into the ponds of the savannahs infested by these eels1 in order to make them discharge their thunderbolts and be readily caught4 ,other fishes--the silurus1 malapterurus1 and so on--are likewise endowed with electric batteries for stunning and capturing their prey4 ,the action of the organs is still a mystery1 as1 indeed1 is the whole subject of animal electricity4 ,nobili and ,matteucci discovered that feeble currents are generated by the excitation of the nerves and the contraction of the muscles in the human subject4 ,electricity promises to become a valuable remedy1 and currents-- continuous1 intermittent1 or alternating--are applied to the body in nervous and muscular affections with good effect2 but this should only be done under medical advice1 and with proper apparatus4 ,in many cases of severe electric shock or lightning stroke1 death is merely apparent1 and the person may be brought back to life by the method of artificial respiration and rhythmic traction of the tongue1 as applied to the victims of drowning or dead faint4 ,a good lightning conductor should not have a higher electrical resistance than #aj ohms from the point to the ground1 including the earth contact4 ,exceptionally good conductors have only about #e ohms4 ,a high resistance in the rod is due either to a flaw in the conductor or a bad earth connection1 and in such a case the rod may be a source of danger instead of security1 since the discharge is apt to find its way through some part of the building to the ground1 rather than entirely by the rod4 ,it is1 therefore1 important to test lightning conductors from time to time1 and the magneto-electric tester of ,siemens1 which we illustrate in figures #ih and #ii1 is very serviceable for the purpose1 and requires no battery4 ,the apparatus consists of a magneto-electric machine ,,at1 which generates the testing current by turning a handle1 and a ,wheatstone bridge4 ,the latter comprises a ring of ,german silver wire1 forming two branches4 ,a contact lever ,p moves over the ring1 and is used as a battery key4 ,a small galvanometer ,g shows the indications of the testing current4 ,a brass sliding piece ,s puts the galvanometer needle in and out of action4 ,there are also several connecting terminals1 b b'1 l1 c41 and a comparison resistance ,r 7figure #ih74 ,a small key ,k is fixed to the terminal l 7figure #ii71 and used to put the current on the lightning-rod1 or take it off at will4 ,a leather bag ,a at one side of the wooden case 7figure #ii7 holds a double conductor leading wire1 which is used for connecting the magneto-electric machine to the bridge4 ,on turning the handle of ,m the current is generated1 and on closing the key ,k it circulates from the terminals of the machine through the bridge and the lightning-rod joined with the latter4 ,the needle of the galvanometer is deflected by it1 until the resistance in the box ,r is adjusted to balance that in the rod4 ,when this is so1 the galvanometer needle remains at rest4 ,in this way the resistance of the rod is told1 and any change in it noted4 ,in order to effect the test1 it is necessary to have two earth plates1 ,e#a and ,e#b1 one 7,el7 that of the rod1 and the other 7,e#b7 that for connecting to the testing apparatus by the terminal b#a 7figure #ii74 ,the whole instrument only weighs about #i lbs4 ,in order to test the earth alone1 a copper wire should be soldered to the rod at a convenient height above the ground1 and terminal screws fitted to it1 as shown at ,t 7figure #ii71 so that instead of joining the whole rod in circuit with the apparatus1 only that part from ,t downwards is connected4 ,the ,hon4 ,r4 ,abercrombie has recently drawn attention to the fact that there are three types of thunderstorm in ,great ,britain4 ,the first1 or squall thunderstorms1 are squalls associated with thunder and lightning4 ,they form on the sides of primary cyclones4 ,the second1 or commonest thunderstorms1 are associated with secondary cyclones1 and are rarely accompanied by squalls ,the third1 or line thunderstorms1 take the form of narrow bands of rain and thunder--for example1 #ajj miles long by #e to #aj miles broad4 ,they cross the country rapidly1 and nearly broadside on4 ,these are usually preceded by a violent squall1 like that which capsized the ,eurydice4 ,the gloom of ,january1 #ahif1 with its war and rumours of war1 was1 at all events1 relieved by a single bright spot4 ,electricity has surprised the world with a new marvel1 which confirms her title to be regarded as the most miraculous of all the sciences4 ,within the past twenty years she has given us the telephone of ,bell1 enabling ,london to speak with ,paris1 and ,chicago with ,new ,york2 the microphone of ,hughes1 which makes the tread of a fly sound like the tramp of an elephant1 as ,lord ,kelvin has said2 the phonograph of ,edison1 in which we can hear again the voices of the dead2 the electric light which glows without air and underwater1 electric heat without fire1 electric power without fuel1 and a great deal more beside4 ,to these triumphs we must now add a means of photographing unseen objects1 such as the bony skeletons in the living body1 and so revealing the invisible4 ,whether it be that the press and general public are growing more enlightened in matters of science1 or that ,professor ,rontgen's discovery appeals in a peculiar way to the popular imagination1 it has certainly evoked a livelier and more sudden interest than either the telephone1 microphone1 or phonograph4 ,i was present when ,lord ,kelvin first announced the invention of the telephone to a ,british audience1 and showed the instrument itself1 but the intelligence was received so apathetically that ,i suspect its importance was hardly realised4 ,it fell to my own lot1 a few years afterwards1 to publish the first account of the phonograph in this country1 and ,i remember that1 between incredulity on the one hand1 and perhaps lack of scientific interest on the other1 a considerable time elapsed before the public at large were really impressed by the invention4 ,perhaps the uncanny and mysterious results of ,rontgen's discovery1 which seem to link it with the black arts1 have something to do with the quickness of its reception by all manner of people4 ,like most1 if not all1 discoveries and inventions1 it is the outcome of work already done by other men4 ,in the early days of electricity it was found that when an electric spark from a frictional machine was sent through a glass bulb from which the air had been sucked by an air pump1 a cloudy light filled the bulb1 which was therefore called an electric egg4 ,hittorf and others improved on this effect by employing the spark from an induction coil and large tubes1 highly exhausted of air1 or containing a rare infusion of other gases1 such as hydrogen4 ,by this means beautiful glows of various colours1 resembling the tender hues of the tropical sky1 or the fleeting tints of the aurora borealis1 were produced1 and have become familiar to us in the well-known ,geissler tubes4 ,crookes1 the celebrated ,english chemist1 went still further1 and by exhausting the bulbs with an improved ,sprengel air-pump1 obtained an extremely high vacuum1 which gave remarkable effects 7page #abj74 ,the diffused glow or cloudy light of the tube now shrank into a single stream1 which joined the sparking points inserted through the ends of the tube as with a luminous thread ,a magnet held near the tube bent the streamer from its course2 and there was a dark space or gap in it near the negative point or cathode1 from which proceeded invisible rays1 having the property of impressing a photographic plate1 and of rendering matter in general on which they impinged phosphorescent1 and1 in course of time1 red-hot4 ,where they strike on the glass of the tube it is seen to glow with a green or bluish phosphorescence1 and it will ultimately soften with heat4 ,these are the famous cathode rays of which we have recently heard so much4 ,apparently they cannot be produced except in a very high vacuum1 where the pressure of the air is about #a-ajjth millionth of an atmosphere1 or that which it is some #ij or #ajj miles above the earth4 ,mr ,crookes regards them as a stream of airy particles electrified by contact with the cathode or negative discharging point1 and repelled from it in straight lines4 ,the rarity of the air in the tube enables these particles to keep their line without being jostled by the other particles of air in the tube4 ,a molecular bombardment from the cathode is1 in his opinion1 going on1 and when the shots1 that is to say1 the molecules of air1 strike the wall of the tube1 or any other body within the tube1 the shock gives rise to phosphorescence or fluorescence and to heat4 ,this1 in brief1 is the celebrated hypothesis of radiant matter1 which has been supported in the ,united ,kingdom by champions such as ,lord ,kelvin1 ,sir ,gabriel ,stokes1 and ,professor ,fitzgerald1 but questioned abroad by ,goldstem1 ,jaumann1 ,wiedemann1 ,ebert1 and others4 ,lenard1 a young ,hungarian1 pupil of the illustrious ,heinrich ,hertz1 was the first to inflict a serious blow on the hypothesis1 by showing that the cathode rays could exist outside the tube in air at ordinary pressure4 ,hertz had found that a thin foil of aluminium was penetrated by the rays1 and ,lenard made a tube having a window of aluminium1 through which the rays darted into the open air4 ,their path could be traced by the bluish phosphorescence which they excited in the air1 and he succeeded in getting them to penetrate a thin metal box and take a photograph inside it4 ,but if the rays are a stream of radiant matter which can only exist in a high vacuum1 how can they survive in air at ordinary pressure8 ,lenard's experiments certainly favour the hypothesis of their being waves in the luminiferous ether4 ,professor ,rontgen1 of ,wirzburg1 profiting by ,lenard's results1 accidentally discovered that the rays coming from a ,crookes tube1 through the glass itself1 could photograph the bones in the living hand1 coins inside a purse1 and other objects covered up or hid in the dark4 ,some bodies1 such as flesh1 paper1 wood1 ebonite1 or vulcanised fibre1 thin sheets of metal1 and so on1 are more or less transparent1 and others1 such as bones1 carbon1 quartz1 thick plates of metal1 are more or less opaque to the rays4 ,the human hand1 for example1 consisting of flesh and bones1 allows the rays to pass easily through the flesh1 but not through the bones4 ,consequently1 when it is interposed between the rays and a photographic plate1 the skeleton inside is photographed on the plate4 ,a lead pencil photographed in this way shows only the black lead1 and a razor with a horn handle only the blade4 ,thanks to the courtesy of ,mr4 ,a4 ,a4 ,campbell ,swinton1 of the firm of ,swinton ,stanton1 the well-known electrical engineers1 of ,victoria ,street1 ,westminster1 a skilful experimentalist1 who was the first to turn to the subject in ,england1 ,i have witnessed the taking of these shadow photographs1 as they are called1 somewhat erroneously1 for radiographs or cryptographs would be a better word1 and shall briefly describe his method4 ,rontgen employs an induction coil insulated in oil to excite the ,crookes tube and yield the rays1 but ,mr4 ,swinton uses a high frequency current1 obtained from apparatus similar to that of ,tesla1 and shown in figure #ajj1 namely1 a high frequency induction coil insulated by means of oil and excited by the continuous discharge of twelve half-gallon ,leyden jars charged by an alternating current at a pressure of #bj1jjj volts produced by an ordinary large induction coil sparking across its high pressure terminals4 ,a vacuum bulb connected between the discharge terminals of the high frequency coil1 as shown in figure #aja1 was illuminated with a pink glow1 which streamed from the negative to the positive pole--that is to say1 the cathode to the anode1 and the glass became luminous with bluish phosphorescence and greenish fluorescence4 ,immediately under the bulb was placed my naked hand resting on a photographic slide containing a sensitive bromide plate covered with a plate of vulcanised fibre4 ,an exposure of five or ten minutes is sufficient to give a good picture of the bones1 as will be seen from the frontispiece4 ,the term shadow photograph requires a word of explanation4 ,the bones do not appear as flat shadows1 but rounded like solid bodies1 as though the active rays passed through their substance4 ,according to ,rontgen1 these x rays1 as he calls them1 are not true cathode rays1 partly because they are not deflected by a magnet1 but cathode rays transformed by the glass of the tube2 and they are probably not ultra-violet rays1 because they are not refracted by water or reflected from surfaces4 ,he thinks they are the missing longitudinal rays of light whose existence has been conjectured by ,lord ,kelvin and others--that is to say1 waves in which the ether sways to and fro along the direction of the ray1 as in the case of sound vibrations1 and not from side to side across it as in ordinary light4 ,be this as it may1 his discovery has opened up a new field of research and invention4 ,it has been found that the immediate source of the rays is the fluorescence and phosphorescence of the glass1 and they are more effective when the fluorescence is greenish-yellow or canary colour4 ,certain salts--for example1 the sulphates of zinc and of calcium1 barium platino-cyanide1 tungstate of calcium1 and the double sulphate of uranyle and potassium--are more active than glass1 and even emit the rays after exposure to ordinary light1 if not also in the dark4 ,salvioni of ,perugia has invented a cryptoscope1 which enables us to see the hidden object without the aid of photography by allowing the rays to fall on a plate coated with one of these phosphorescent substances4 ,already the new method has been applied by doctors in examining malformations and diseases of the bones or internal organs1 and in localising and extracting bullets1 needles1 or other foreign matters in the body4 ,there is little doubt that it will be very useful as an adjunct to hospitals1 especially in warfare1 and1 if the apparatus can be reduced in size1 it will be employed by ordinary practitioners4 ,it has also been used to photograph the skeleton of a mummy1 and to detect true from artificial gems4 ,however1 one cannot now easily predict its future value1 and applications will be found out one after another as time goes on4 ,,chapter ,x4 ,,the ,,wireless ,,telegraph4 ,magnetic waves generated in the ether 7see pp4 #ec-ie7 by an electric current flowing in a conductor are not the only waves which can be set up in it by aid of electricity4 ,a merely stationary or static charge of electricity on a body1 say a brass ball1 can also disturb the ether2 and if the strength of the charge is varied1 ether oscillations or waves are excited4 ,a simple way of producing these electric waves in the ether is to vary the strength of charge by drawing sparks from the charged body4 ,of course this can be done according to the ,morse code2 and as the waves after travelling through the ether with the speed of light are capable of influencing conductors at a distance1 it is easy to see that signals can be sent in this way4 ,the first to do so in a practical manner was ,signer ,marconi1 a young ,italian hitherto unknown to fame4 ,in carrying out his invention1 ,marconi made use of facts well known to theoretical electricians1 one of whom1 ,dr1 ,oliver ,j4 ,lodge1 had even sent signals with them in #ahid2 but it often happens in science as in literature that the recognised professors1 the men who seem to have everything in their favour--knowledge1 even talent--the men whom most people would expect to give us an original discovery or invention1 are beaten by an outsider whom nobody heard of1 who had neither learning1 leisure1 nor apparatus1 but what he could pick up for himself4 ,marconi produces his waves in the ether by electric sparks passing between four brass balls1 a device of ,professor ,righi1 following the classical experiments of ,heinrich ,hertz4 ,the balls are electrified by connecting them to the well-known instrument called an induction coil1 sometimes used by physicians to administer gentle shocks to invalids2 and as the working of the coil is started and stopped by an ordinary telegraph key for interrupting the electric current1 the sparking can be controlled according to the ,morse code4 ,in our diagram1 which explains the apparatus1 the four balls are seen at ,d1 the inner and larger pair being partly immersed in vaseline oil1 the outer and smaller pair being connected to the secondary or induced circuit of the induction coil ,c1 which is represented by a wavy line4 ,the primary or inducing circuit of the coil is connected to a battery ,b through a telegraph signalling key ,k1 so that when this key is opened and closed by the telegraphist according to the ,morse code1 the induction coil is excited for a longer or shorter time by the current from the battery1 in agreement with the longer and shorter signals of the message4 ,at the same time longer or shorter series of sparks corresponding to these signals pass across the gaps between the four balls1 and give rise to longer or shorter series of etheric waves represented by the dotted line4 ,so much for the ,transmitter4 ,but how does ,marconi transform these invisible waves into visible or audible signals at the distant place8 ,he does this by virtue of a property discovered by ,mr4 ,s4 ,a4 ,varley as far back as #ahff1 and investigated by ,mr4 ,e4 ,branly in #ahhi4 ,they found that powder of metals1 carbon1 and other conductors1 while offering a great resistance to the passage of an electric current when in a loose state1 coheres together when electric waves act upon it1 and opposes much less resistance to the electric current4 ,it follows that if a ,morse telegraph instrument at the distant place be connected in circuit with a battery and some loose metal dust1 it can be adjusted to work when the etheric waves pass through the dust1 and only then4 ,in the diagram ,r is this ,morse ,receiver joined in circuit with a battery ,b#a2 and a thin layer of nickel and silver dust1 mixed with a trace of mercury1 is placed between two cylindrical knobs or electrodes of silver fused into the glass tube d1 which is exhausted of air like an electric glow lamp4 ,now1 when the etheric waves proceeding from the transmitting station traverse the glass of the tube and act upon the metal dust1 the current of the battery ,b#a works the ,morse receiver1 and marks the signals in ink on a strip of travelling paper4 ,inasmuch as the dust tends to stick together after a wave passes through it1 however1 it requires to be shaken loose after each signal1 and this is done by a small round hammer head seen on the right1 which gives a slight tap to the tube4 ,the hammer is worked by a small electromagnet ,e1 connected to the ,morse instrument1 and another battery b in what is called a relay circuit2 so that after the ,morse instrument marks a signal1 the hammer makes a tap on the tube4 ,as this tap has a bell-like sound1 the telegraphist can also read the signals of the message by his ear4 ,two self-induction bobbins1 ,l ,ll1 a well-known device of electricians for opposing resistance to electric waves1 are included in the circuit of the ,morse instrument the better to confine the action of the waves to the powder in the tube4 ,further1 the tube d is connected to two metal conductors ,v ,vl1 which may be compared to resonators in music4 ,they can be adjusted or attuned to the electric waves as a string or pipe is to sonorous waves4 ,in this way the receiver can be made to work only when electric waves of a certain rate are passing through the tube1 just as a tuning-fork resounds to a certain note2 it being understood that the length of the waves can be regulated by adjusting the balls of the transmitter4 ,as the etheric waves produced by the sparks1 like ripples of water caused by dropping a stone into a pool1 travel in all directions from the balls1 a single transmitter can work a number of receivers at different stations1 provided these are tuned by adjusting the conductors ,v ,vl to the length of the waves4 ,this indeed was the condition of affairs at the time when the young ,italian transmitted messages from ,france to ,england in ,march1 #ahii1 and it is a method that since has been found useful over limited distances4 ,but to the inventor there seemed no reason why wireless telegraphy should be limited by any such distances4 ,accordingly he immediately developed his method and his apparatus1 having in mind the transmission of signals over considerable intervals4 ,the first question that arose was the effect of the curvature of the ,earth and whether the waves follow the surface of the ,earth or were propagated in straight lines1 which would require the erection of aerial towers and wires of considerable height4 ,then there was the question of the amount of power involved and whether generators or other devices could be used to furnish waves of sufficient intensity to traverse considerable distances4 ,little by little progress was made and in ,january1 #aija1 wireless communication was established between the ,isle of ,wight and ,lizard in ,cornwall1 a distance of #ahf miles with towers less than #cjj feet in height1 so that it was demonstrated that the curvature of the ,earth did not seriously affect the transmission of the waves1 as towers at least a mile high would have been required in case the waves were so cut off4 ,this was a source of considerable encouragement to ,marconi1 and his apparatus was further improved so that the resonance of the circuit and the variation of the capacity of the primary circuit of the oscillation transformer made for increased efficiency4 ,the coherer was still retained and by the end of #aijj enough had been accomplished to warrant ,marconi in arranging for trans-,atlantic experiments between ,poldhu1 ,cornwall and the ,united ,states1 stations being located on ,cape ,cod and in ,newfoundland4 ,the trans-,atlantic transmission of signals was quite a different matter from working over #ajj miles or so in ,great ,britain4 ,the single aerial wire was supplanted by a set of fifty almost vertical wires1 supported at the top by a horizontal wire stretched between two masts #aeg #a_/b feet high and #eb #a_/b feet apart1 converging together at the lower end in the shape of a large fan4 ,the capacity of the condenser was increased and instead of the battery a small generator was employed so that a spark #a #a_/b inches in length would be discharged between spheres #c inches in diameter4 ,at the end of the year #aija temporary stations at ,newfoundland were established and experiments were carried on with aerial wires raised in the air by means of kites4 ,it was here realized that various refinements in the receiving apparatus were necessary1 and instead of the coherer a telephone was inserted in the secondary circuit of the oscillation transformer1 and with this device on ,february #abth the first signals to be transmitted across the ,atlantic were heard4 ,these early experiments were seriously affected by the fact that the antennae or aerial wires were constantly varying in height with the movement of the kites1 and it was found that a permanent arrangement of receiving wires1 independent of kites or balloons1 was essential4 ,yet it was demonstrated at this time that the transmission of electric waves and their detection over distances of #bjjj miles was distinctly possible4 ,a more systematic and thorough test occurred in ,february1 #aijb1 when a receiving station was installed on the steamship ,philadelphia1 proceeding from ,southampton to ,new ,york4 ,the receiving aerial was rigged to the mainmast1 the top of which was #aig feet above the level of the sea1 and a syntonic receiver was employed1 enabling the signals to be recorded on the tape of an ordinary ,morse recorder4 ,on this voyage readable messages were received from ,poldhu up to a distance of #aeea miles1 and test letters were received as far as #bjii miles4 ,it was on this voyage that ,marconi made the interesting discovery of the effect of sunlight on the propagation of electric waves over great distances4 ,he found that the waves were absorbed during the daytime much more than at night and he eventually reached the conclusion that the ultraviolet light from the sun ionized the gaseous molecules of the air1 and ionized air absorbs the energy of the electric waves1 so that the fact was established that clear sunlight and blue skies1 though transparent to light1 serve as a fog to the powerful ,hertzian waves of wireless telegraphy4 ,for that reason the transmission of messages is carried on with greater facility on the shores of ,england and ,newfoundland across the ,north ,atlantic than in the clearer atmosphere of lower latitudes4 ,but atmospheric conditions do not affect all forms of waves the same1 and long waves with small amplitudes are far less subject to the effect of daylight than those of large amplitude and short wave length1 and generators and circuits were arranged to produce the former4 ,but the difficulty did not prove insuperable1 as ,marconi found that increasing the energy of the transmitting station during the daytime would more than make up for the loss of range4 ,the experiments begun at ,newfoundland were transferred to ,nova ,scotia1 and at ,glace ,bay in #aijb was established a station from which messages were transmitted and experimental work carried on until its work was temporarily interrupted by fire in #aiji4 ,here four wooden lattice towers1 each #baj feet in height1 were built at the corner of a square #bjj feet on a side1 and a conical arrangement of #djj copper wires supported on stays between the tops of the towers and connected in the middle at the generating station was built4 ,additional machinery was installed and at the same time a station at ,cape ,cod for commercial work was built4 ,in ,december1 #aijb1 regular communication was established between ,glace ,bay and ,poldhu1 but it was only satisfactory from ,canada to ,england as the apparatus at the ,poldhu station was less powerful and efficient than that installed in ,canada4 ,the transmission of a message from ,president ,roosevelt to ,king ,edward marked the practical beginning of trans-,atlantic wireless telegraphy4 ,by this time a new device for the detection of messages was employed1 as the coherer we have described even in its improved forms was found to possess its limitations of sensitiveness and did not respond satisfactorily to long distance signals4 ,a magnetic detector was devised by ,marconi while other inventors had contrived electrolytic1 mercurial1 thermal1 and other forms of detector1 used for the most part with a telephone receiver in order to detect minute variations in the current caused by the reception of the electro-magnetic waves4 ,with one of ,marconi's magnetic detectors signals from ,cape ,cod were read at ,poldhu4 ,in #aijc wireless telegraphy had reached such a development that the transmission of news messages was attempted in ,march and ,april of that year4 ,but the service was suspended1 owing to defects which manifested themselves in the apparatus1 and in the meantime a new station in ,ireland was erected4 ,but there was no cessation of the practical experiments carried on1 and in #aijc the ,cunard steamship ,lucania received1 during her entire voyage across from ,new ,york to ,liverpool1 news transmitted direct from shore to shore4 ,in the meantime intercommunication between ships had been developed and the use of wireless in naval operations was recognized as a necessity4 ,various improvements from time to time were made in the aerial wires1 and in #aije a number of horizontal wires were connected to an aerial of the inverted cone type previously used4 ,the directional aerial with the horizontal wires was tried at ,glace ,bay1 and adopted for all the long distance stations1 affording considerable strengthening of the received signals at ,poldhu stations4 ,likewise improvements in the apparatus were effected at both trans-,atlantic stations1 consisting of the adoption of air condensers composed of insulated metallic plate suspended in the air1 which were found much better than the condensers where glass was previously used to separate the plates4 ,for producing the energy employed for transmitting the signals a high tension continuous current dynamo is used4 ,an oscillatory current of high potential is produced in a circuit which consists of rapidly rotating disks in connection with the dynamo and suitable condensers4 ,the production of electric oscillations can be accomplished in several ways and waves of the desired frequency and amplitude produced4 ,thus in #aijc it was found by ,poulsen1 elaborating on a principle first discovered by ,duddell1 that an oscillatory current may be derived from an electric arc maintained under certain conditions and that undamped high frequency waves so produced were suitable for wireless telegraphy4 ,this discovery was of importance1 as it was found that the waves so generated were undamped1 that is1 capable of proceeding to their destination without loss of amplitude4 ,on this account they were especially suitable for wireless telephony where they were early applied1 as it was found possible so to arrange a circuit with an ordinary microphone transmitter that the amplitude of the waves would be varied in harmony with the vibrations of the human voice4 ,these waves so modulated could be received by some form of sensitive wave detector at a distant station and reproduced in the form of sound with an ordinary telephone receiver4 ,with undamped waves from the arc and from special forms of generators wireless telephony over distances as great as #bjj miles has been accomplished and over shorter distances1 especially at sea and for sea to shore1 communication has found considerable application4 ,it is1 however1 an art that is just at the beginning of its usefulness1 standing in much the same relation to wireless telegraphy that the ordinary telephone does to the familiar system employing metallic conductors4 ,on the spark and arc systems various methods of wireless telegraphy have been developed and improved so that ,marconi no longer has any monopoly of methods or instruments4 ,various companies and government officials have devised or modified systems so that to-day wireless is practically universal and is governed by an international convention to which leading nations of the world subscribe4 ,one of the recent features of wireless telegraphy of interest is the success of various directional devices4 ,as we have seen1 various schemes were tried by ,marconi ranging from metallic reflectors used by ,hertz in his early experiments with the electric waves to the more successful arrangement of aerial conductors4 ,in ,europe ,bellini and ,tosi have developed a method for obtaining directed aerial waves which promises to be of considerable utility1 enabling them to be projected in a single direction just as a searchlight beam and thus restrict the number of points at which the signals could be intercepted and read4 ,likewise an arrangement was perfected which enabled a station to determine the direction in which the waves were being projected and consequently the bearing of another vessel or lighthouse or other station4 ,the fundamental principle was the arrangement of the antennae1 two triangular systems being provided on the same mast1 but in one the current is brought down in a perpendicular direction4 ,the action depends upon the difference of the current in the two triangles4 ,wireless telegraph apparatus is found installed in almost every seagoing passenger vessel of large size engaged in regular traffic1 and as a means of safety as well as a convenience its usefulness has been demonstrated4 ,thus on the ,north ,atlantic the largest liners are never out of touch with land on one side of the ocean or the other1 and news is supplied for daily papers which are published on shipboard4 ,every ship in this part of the ocean equipped with the ,marconi system1 for example1 is in communication on an average with four vessels supplied with instruments of the same system every twenty-four hours4 ,in case of danger or disaster signals going out over the sea speedily can bring succour1 as clearly was demonstrated in the case of the collision between the ,white ,star steamship ,republic and the steamship ,florida on ,january #bf1 #aiji4 ,here wireless danger messages were sent out as long as the ,republic was afloat and its wireless apparatus working4 ,these brought aid from various steamers in the vicinity and the passengers were speedily transferred from the sinking ,republic4 ,on ,april #ae1 #aiab1 the ,white ,star liner ,titanic1 the largest ship afloat1 sank off ,newfoundland1 after colliding with an iceberg4 ,wireless ,,sos calls for help brought several steamships to the scene1 and #gjc persons from a total of #b1bjf1 were rescued4 ,on ,october #i1 #aiac1 the ,uranium liner ,volturno caught fire in mid- ocean1 and her wireless calls brought ten steamships to her aid1 which1 despite a heavy sea1 rescued #ecb persons from a total of #feg4 ,again1 on ,november #ad1 #aiac1 the ,spanish steamship ,balmes caught fire off ,bermuda1 and at her wireless call the ,cunard liner ,pannonia saved all of her passengers--#ajc4 ,the ,titanic horror led the principal maritime nations to take immediate steps to perfect their wireless systems1 and the installation of apparatus and operators soon became a prime requisite of the equipment of the world's shipping4 ,wireless telegraphy has been developed to great efficiency in all the leading navies1 and powerful plants are installed on all warships4 ,the ,united ,states1 ,great ,britain1 and ,germany1 most noticeably1 have established shore stations1 by which they can talk all around the world from any ship or station4 ,in operation secrecy is most important4 ,for in the navy practically all important messages are sent in code or cipher under all conditions while in commercial work the tapping of land wires or the stealing of messages while illegal is physically possible for the evil disposed yet has never proved in practice a serious evil4 ,the problem of interference1 however1 seems to have been fairly solved by the large systems though the activity of amateurs is often a serious disturbance for government and other stations4 ,despite the progress of wireless telegraphy it has not yet supplanted the submarine cable and the land wire1 and in conservative opinion it will be many years before it will do so4 ,in fact1 since ,marconi's work there has been no diminution in the number or amount of cables laid and the business handled1 nor is there prospect of such for years to come4 ,while the cable has answered admirably for telegraphic purposes yet for telephony over considerable distances it has failed entirely so that wireless telephony over oceans starts with a more than favorable outlook4 ,but wireless telegraphy to a large extent has made its own field and here its work has been greatly successful4 ,thus when ,peary's message announcing his discovery of the ,north ,pole came out of the ,frozen ,north1 it was by way of the wireless station on the distant ,labrador coast that it reached an anxious and interested civilization4 ,it is this same wireless that watches the progress of the fishing fleets at stations where commercial considerations would render impossible the maintenance of a submarine cable4 ,it is the wireless telegraph that maintains communication in the interior of ,alaska and between islands in the ,pacific and elsewhere where conditions of development do not permit of the more expensive installation of submarine cable or climatic or other conditions render impossible overland lines4 ,at sea its advantages are obvious4 ,everywhere the ether responds to the impulses of the crackling sparks1 and even from the airship we soon may expect wireless messages as the few untrodden regions of our globe are explored4 ,,chapter ,,xl ,,electro-,,chemistry ,,and ,,electro-,,metallurgy4 ,in no department of the application of electricity to practical work has there been a greater development than in electro- metallurgy and electro-chemistry4 ,to-day there are vast industries depending upon electrical processes and the developments of a quarter of a century have been truly remarkable4 ,already more than one-half of the copper used in the arts is derived by electrolytic refining4 ,the production of aluminum depends entirely on electricity1 the electric furnace as a possible rival to the blast furnace for the production of iron and steel is being seriously considered1 and many other metallurgical processes are being undertaken on a large scale4 ,we have seen in our chapter on ,electrolysis how a metal may be deposited from a solution of its salt and how this process could be used for deriving a pure metal or for plating or coating with the desired metal the surface of another metal or one covered with graphite4 ,in the following pages it is intended to take up some of the more notable accomplishments in this field achieved by electricity1 which have been developed to a state of commercial importance4 ,the electric arc not only supplies light1 but heat of great intensity which the electrical engineer as well as the pure scientist has found so valuable for many practical operations4 ,it is of course obvious that for most chemical operations1 and especially in the field of metallurgy1 heat is required for the separation of combinations of various elements1 for their purification1 as well as for the combination with other elements into alloys or compounds of direct utility4 ,the usual method of generating heat is by the combustion of some fuel1 such as coal1 coke1 gas or oil1 and this has been utilized for hundreds of years in smelting metals and ores and in refining the material from a crude state4 ,now it may happen that a nation or region may be rich in metalliferous ores1 but possess few1 if any1 coal deposits4 ,accordingly the ore must be mined and transported considerable distances for treatment and the advantages of manufacturing industries are lost to the neighborhood of its original production4 ,but if water power is available1 as it is in many mountainous countries where various ores are found1 then this power can be transformed into electricity which is available as power not only in various manufacturing operations1 but for primary metallurgical work in smelting the ores and obtaining the metal therefrom4 ,a striking instance of this is the kingdom of ,sweden1 which contains but little coal1 yet is rich in minerals and in water power1 so that its waterfalls have been picturesquely alluded to as the country's white coal4 ,likewise1 at ,niagara ,falls a portion of the vast water power developed there has been used in the manufacture of aluminum1 calcium carbide1 carborundum1 and other materials1 while at other points in the ,united ,states and ,canada1 not to mention ,europe1 large industries where electricity is used for metallurgical or chemical work are carried on and the erection of new plants is contemplated4 ,the application of electricity to metallurgical and chemical work has been1 in nearly all cases1 the result of scientific research1 and elaborate experimental laboratories are maintained by the various corporations interested in the present or future use of electrical processes4 ,it is recognized by many of the older workers in this field that electrical developments are bound to come in the near future1 and while they have not installed such appliances in their works yet they are keeping close watch of present developments1 and in many cases experimental investigation and research is being carried on where electrical methods have not yet been introduced generally into the plant4 ,prior to #ahhf the refining of copper was the only electro- metallurgical industry and at that time it was carried on on a very limited scale4 ,to-day the production of electrolytic copper as an industry is second in importance only to the actual production of that metal4 ,from the small refinery started by ,james ,elkington at ,pembury in ,south ,wales1 a vast industry has developed in which there has been a change in the size of operations and in the details of methods rather than in the fundamental process4 ,for a solution of copper sulphate is employed as the electrolyte1 blocks of raw copper as the anodes1 and thin sheets of pure copper as the cathodes4 ,the passage of the electric current1 as we have seen on page #gi1 in the chapter on ,electrolysis1 is able to decompose the copper in the electrolyte and to precipitate chemically pure copper on the cathode1 the copper of the solution being replenished from the raw material used as the anode by which the current is passed into the bath4 ,at this ,welsh factory #bej tons yearly were produced1 and small earthenware pots sufficed for the electrolyte4 ,thirty years later one ,american factory alone was able to produce at least #cej tons of electrolytic copper in twenty-four hours1 and over #djj1jjj tons is the aggregate output of the refineries of the world1 which is about #ec per cent1 of the total raw copper production4 ,of this amount #he per cent1 comes from ,american refineries1 whose output has more than doubled since #aijj4 ,the chief reason for this increased output of electrolytic copper has been the great demand for its use in the electrical industries where not only a vast amount is consumed1 but where copper of high purity1 to give the maximum conductivity required by the electrical engineer1 is demanded4 ,when it is realized that every dynamo is wound with copper wire and that the same material is used for the trolley wire and for the distribution wires in electric lighting1 it will be apparent how the demand for copper has increased in the last quarter of a century4 ,electrolytic methods not only supply a purer article and are economical to operate1 especially if there is water power in the vicinity1 but the copper ores contain varying amounts of silver and gold which can be recovered from the slimes obtained in the electrolytic process4 ,wherever possible machinery has been substituted for hand labor1 the raw copper anodes have been cast1 and the charging and discharging of the vats is carried on by the most modern mechanical methods in which efficiency and economy are secured4 ,on the chemical side of the process attempts have been made to improve the electrolyte1 notably by the addition of a small amount of hydrochloric acid to prevent the loss of silver in the slimes1 and this part of the work is watched with quite as much care as the other stages4 ,electric furnaces have also been constructed for smelting copper ores1 but these have not found wide application1 and the problem is one of the future4 ,for the most part the copper electrically refined is produced in an ordinary smelter4 ,the mints of the ,united ,states are now all equipped with electrolytic refining plants to produce the pure metal needed for coinage and they have proved most satisfactory and economical4 ,as the electrolytic production of copper is an industry of great present importance1 so the production of iron and steel by electricity promises to be of the greatest future importance4 ,electric furnaces for making steel are now maintained1 and the industry has passed beyond an experimental condition4 ,but it has not reached the point where it is competing with the ,bessemer or the open hearth process of the manufacture of steel1 while for the smelting of iron ores the electric furnace has not yet been found practical from an economic standpoint4 ,before #ahhj ,sir ,william ,siemens showed that an electric arc could be used to melt iron or steel in a crucible1 and he patented an electric crucible furnace which was the first attempt to use electricity in iron and steel manufacture4 ,he stated that the process would not be too costly and that it had a great future before it4 ,this was an application of the intense heat of the arc1 which supplies a higher temperature than any source known except that of the sun4 ,this heat is used to melt the metal1 in which condition various impurities can be removed and necessary ingredients added4 ,siemens' furnace did not find extensive application1 largely on account of the great metallurgical developments then taking place in the iron industry and the thorough knowledge of metallurgical processes as carried on1 possessed by metallurgical engineers4 ,but the idea by no means languished1 and in #ahii ,paul ,heroult and other electro-metallurgists were active in developing a practical electric furnace for iron and steel work4 ,the ,swedish engineer1 ,f4 ,a4 ,kjellin1 was also active and as the result of the efforts of these and other workers1 by #aiji electric furnaces were employed1 not only in the manufacture of special steels whose composition and making were attended with special care1 but for rails and structural material4 ,there were reported to be between thirty and forty electric steel plants in various countries1 and the outlook for the future was distinctly bright4 ,the application of electro- metallurgy at this time was confined to the manufacture of steel1 as the smelting of iron had not emerged from the experimental stage of its development1 though extensive trials on a large scale of various furnaces have been undertaken in ,europe and by the ,canadian government at ,sault ,ste4 ,marie1 where the ,heroult furnace1 soon to be described1 was employed4 ,electro-metallurgy of steel1 as in all utilization of electrical power1 depends upon obtaining electricity at a reasonable cost1 and then utilizing the heat of the arc or of the current in the most practical and economical form4 ,one of the pioneer furnaces for this purpose which has seen considerable development and practical application is the ,heroult furnace1 which is a tilting furnace of the crucible type1 whose operation depends upon both the heat of the arc and on the heat produced by the resistance of the molten material4 ,in the ,heroult process the impurities of the molten iron are washed out by treatment with suitable slags4 ,the furnace consists of a crucible in the form of a closed shallow iron tank1 thickly lined with dolomite and magnazite brick1 with a hearth of crushed dolomite4 ,the electric current enters the crucible through two massive electrodes of solid carbon1 #gj inches in length and #ad inches in diameter1 so mounted that they can be moved either vertically or horizontally by the electrician in charge4 ,these electrodes are water-jacketed to reduce the rate of consumption4 ,the furnace contains an inlet for an air blast and openings in its covering for charging the material and for the escape of the gases4 ,the actual process of steel-making consists of charging the crucible with steel scrap1 pig iron1 iron ore1 and lime of the proper quality and in the right proportions1 placing this material on the hearth of the furnace4 ,combined arc and resistance heating is applied to raise the charge to the melting point4 ,the current is of #abj volts or the same as that used in an ordinary incandescent lighting circuit1 but is alternating and of #d1jjj amperes4 ,this is for a three-ton furnace4 ,as the material melts the lime and silicates form a slag which fuses rapidly and covers the iron and steel in the crucible1 so that the molten bath is protected from the action of the gases which are liberated and the oxygen in the atmosphere4 ,the next step in the process is to lower the electrodes until they just touch beneath the surface of the molten slag so that subsequent heating is due not to the effect of the arc but to the resistance which the bath offers to the passage of the current4 ,air from an air blast is introduced into the crucible to oxidize the impurities of the metal1 particularly the sulphur and the phosphorus which are carried into the slag and this is removed by the tilting of the furnace4 ,fresh quantities of lime1 etc41 are added1 and the operation is repeated until a comparatively pure metal remains1 when an alloy high in carbon is added and whatever other constituents are desired for the finished steel4 ,the charge is then tipped into the casting ladle and the part of the electric furnace is finished4 ,for three tons of steel eight to ten hours are required in the ,heroult crucible furnace4 ,furnaces of an altogether different type are those employing an alternating current1 such as the ,kjellin and ,rochling furnaces1 where the metal to be heated really forms the secondary circuit of a large and novel form of transformer which in principle is analogous to the familiar transformer seen to step down the potential of alternating current as for house lighting4 ,for such a transformer the primary coil is formed of heavy wire and the secondary circuit is the molten metal which is contained in an annular channel4 ,the current obtained in the metal is of considerable intensity1 but at lower potential than that in the primary coil1 and roughly is equal to that of the primary multiplied by the number of turns in the coil4 ,the condition is similar to that in the ordinary induction coil where the current from a battery at low potential flows around a coil of a few turns and is surrounded by a second coil with a large number of turns of fine wire in which current of small intensity but of high potential is generated4 ,in the induction furnace the reverse takes place and the current flowing in the metal derived from that of the heavy coil in the primary is of great intensity4 ,for this type of furnace molten metal is required and the furnace is never entirely emptied1 so that its process is continuous4 ,the temperature attained is not as high as in the arc furnace1 so that the raw materials used have to be of a high degree of purity1 and this has proved a restriction of the field of usefulness of this type of furnace in many cases4 ,it1 however1 has been improved recently and two rings of molten metal employed instead of one so that a wide centre trough is obtained in which the metal is subjected to ordinary resistance heat by direct or alternating currents4 ,this furnace permits of various metallurgical operations and the elimination of impurities as in the ,heroult type4 ,a third type of furnace that is meeting with some extensive use is the ,giroud1 which1 like the ,heroult furnace1 is based on the arc and resistance in principle1 but in its construction has a number of different features4 ,as the current passes horizontally from the upper electrodes through the slag and molten metal in the furnace chamber to the base electrodes of the furnace1 it permits of the easy regulation of the arcs and the use of lower electromotive force1 while there is only one arc in the path of the current instead of two as in the ,heroult type4 ,sufficient quantities of steel have been made in electric furnaces to permit of the determination of the quality of the product as well as the economy of the process4 ,it has been found in ,germany that rail steel made in the induction furnace has a much higher bending and breaking limit than ordinary ,bessemer or ,thomas rail steel1 and in ,germany in #aijh rails so made commanded a considerably higher price per ton than those of ordinary rail steel4 ,after trial orders had proved satisfactory1 in #aijh #e1jjj tons of rails were ordered for the ,italian and ,swiss governments at a ,german works1 where furnaces of eight tons capacity had been installed4 ,in the ,united ,states only a few electric steel furnaces are in operation1 and these1 for the most part1 for purposes of demonstration and experiment4 ,but in ,europe the industry is well established1 and while at present small1 is constantly growing and possesses an assured future4 ,in addition to the manufacture of steel1 the application of the electric furnace for producing what are known as ferro-alloys1 or alloys of iron1 silicon1 chromium1 manganese1 tungsten and vanadium1 is now a large and important industry4 ,special steels have their uses in different mechanical applications and the advantage of alloying them with the rarer metals has been demonstrated for several important purposes1 as for example1 the use of chrome steel for armor plate1 and steel containing vanadium for parts of motor cars4 ,these industries for the most part contain electric arc furnaces and have1 as their object1 the manufacture of ferro-alloys1 which are introduced into the steel1 it having been found advantageous to use the rare metals in this form rather than in their crude state4 ,there is one electro-metallurgical process that has made possible the production in commercial form and for ordinary use of a metal that once was little more than a chemical curiosity4 ,in #ahhe there were produced #c4ab tons of aluminum1 and its value was roughly estimated at about #ab a pound4 ,by #aijh ,america alone produced over #i1jjj tons valued at over #ejj1jjj1jjj1 while ,european manufacturers were also large producers4 ,in #ahhh the electrolytic manufacture of aluminum was commenced in ,america and in the following year it was begun in ,switzerland4 ,aluminum is formed by the electrolysis of the aluminum oxide in a fused bath of cryolite and fluorspar4 ,the aluminum may be obtained in the form of bauxite1 and is produced in large rectangular iron pots with a thick carbon lining4 ,the pot itself is the cathode1 while large graphite rods suspended in the bath serve as the anodes4 ,after the arc is formed and the heat of the bath rises to a sufficient degree the material is decomposed and the metal is separated out so that it can be removed by ladling or with a siphon4 ,the application of heat to obtain this metal previous to the invention of the electric furnace could only be considered a laboratory problem and the expense involved did not permit of commercial application4 ,now1 however1 aluminum is universally available and with the expiration of certain patents1 the material has sold as low as #be cents a pound4 ,electrolytic methods serve also for the refining of nickel and for the production of lead1 and as in other fields of metallurgy1 these processes are attracting the attention of chemists and of engineers4 ,while tin as yet has not yielded to electrolytic or electro-thermal methods with any success1 the removal of tin from tin scraps and cuttings has been carried on with considerable success4 ,with zinc the electrolytic and electro-thermal processes have not been able yet to compete with the older metallurgical method of distillation1 but an important industry is electro- galvanizing1 where a solution of zinc sulphate is deposited on iron and gives a protective coating4 ,experimental methods with the use of electricity in extracting zinc from its ores are being tested at various ,european plants1 but the matter has not yet reached a commercial scale4 ,one of the earliest notable uses of the electric furnace in a large electro-chemical industry was for the production of carborundum1 a carbide of silicon1 which is remarkably useful as an abrasive1 being available in the manufacture of grinding stones and other like purposes to replace emery and corundum4 ,it is produced by the use of a simple electric furnace of the resistance type1 where coke1 sand1 and sawdust are heated to a temperature of between #bjjj degrees and #cjjj degrees ,c4 ,the chemical reaction involves the production of carbon monoxide1 and gives a carbide of silicon1 a crystalline solid which has the excellent abrasive properties mentioned4 ,the manufacture was first started by its inventor1 ,e4 ,g4 ,acheson1 about #ahia on a small scale1 and in the following year #a1jjj pounds of the material were produced at the ,niagara ,falls works4 ,within fifteen years its output had increased to well over six million pounds4 ,the electric furnaces at ,niagara ,falls have supplied many interesting electro-chemical processes4 ,after making a carbide in the electric furnace it was found possible to decompose it by further increasing the heat to a point where the second element is volatilized and the pure carbon in the form of artificial graphite remains4 ,in more recent work the carbide containing the silicon has been done away with and ordinary anthracite coal used as a charge from which the pure graphite is obtained4 ,this graphite has been found especially useful in electrical work as for electrodes1 while a more recent process enables a soft variety of graphite to be obtained which becomes a competitor of the natural material4 ,one of the most interesting of the many electro-chemical processes is the heating of lime and coke in the electric furnace so as to obtain a product in the form of calcium carbide1 which1 on solution in water1 forms acetylene gas1 a useful and valuable illuminant4 ,this process dates from #ahic when ,t4 ,l4 ,willson in the ,united ,states first started its manufacture on a large scale1 and the great electrochemist1 ,henri ,moissin1 about the same time independently invented a similar process as a result of his notable work with the electric furnace4 ,the process involves merely a transformation at a high temperature1 a portion of the carbon in the form of coke1 uniting with pulverized lime to give the calcium carbide or ,ca,c#b4 ,now this material1 when water is added to it1 decomposes1 and acetylene or ,c#b;,h#b is formed1 which is a gas of high illuminating value as the carbon separates and glows brightly after being heated to incandescence in the flame4 ,the electric furnace at ,niagara ,falls has been able to produce still another combination in the form of siloxicon by heating carbon and silicon to a temperature slightly below that required to produce carborundum4 ,this product is a highly refractory material and is valuable for the manufacture of crucibles1 muffles1 bricks1 etc41 for work where extreme temperatures are employed4 ,the electric furnace enables various elements to be isolated1 such4 as silicon1 sodium1 and phosphorus1 and when obtained in their pure state they find wide application4 ,the most important electro-chemical work of the future is to devise some means of obtaining nitrogen from the air4 ,it is stated by scientists that the nitrogen of the soil is being exhausted and that at some future time the ,earth may not be able to bear crops sufficient for the sustenance of man1 unless some artificial means be found to replenish the nitrogen4 ,unlimited supplies of nitrogen exist in the air1 but to fix it with other materials in such form that it will be useful as a fertilizer has been one of the problems to which the electro-chemists have recently devoted much attention4 ,by the use of the electric arc and passing air through a furnace1 various substances have been tried to take up the nitrogen of the air4 ,thus when calcium carbide is heated and brought into contact with nitrogen one atom of carbon is given up and two atoms of nitrogen take its place1 resulting in the production of cyanamide4 ,other important electro-chemical processes are involved in the electrolysis of the various alkaline salts to obtain metallic sodium and such products as chlorates4 ,thus by the electrolysis of sodium chloride metallic sodium and chlorine is obtained4 ,from the metallic sodium solid caustic soda is then derived by a secondary reaction1 while the chlorine is combined with lime to form chloride of lime or bleaching powder4 ,in some processes the electrolysis affords directly an alkaline hypochlorite or a chlorate1 the former being of wide commercial use as a bleaching agent in textile works and in the paper industry4 ,the same process employed in the electrolysis of sodium salts is used in the case of magnesium and calcium4 ,electrolysis is also made use of in the manufacture of chloroform and iodoform1 as the chlorine or iodine which is produced in the electrolytic cell is allowed to act upon the alcohol or acetone under such conditions that chloroform or iodoform is produced4 ,electro-chemistry plays an important part in many other industries whose omission from our description must not be considered as indicating any lack of their importance4 ,new processes constantly are being discovered which may range all the way from the production of artificial gems to the wholesale production of the most common chemicals used in the arts4 ,in many branches of chemical industry manufacturing processes have been completely changed1 and from the research laboratories1 which all large progressive manufacturers now maintain1 as well as from workers in universities and scientific schools1 new methods and discoveries are constantly forthcoming4 ,,chapter ,,xii4 ,,electric ,,railways4 ,the electric railway of ,dr4 ,werner von ,siemens constructed at ,berlin in #ahgi was the forerunner of a number of systems which have had the effect of changing materially the problems of transportation in all parts of the world4 ,the electric railway not only was found suitable as a substitute for the tramway with its horse-drawn car1 but far more economical than the cable cars1 which were installed to meet the transportation problems of large cities with heavy traffic1 or1 as in the case of certain cities on the ,pacific slope1 where heavy grades made transportation a serious problem4 ,furthermore1 the electric railway was found serviceable for rural lines where small steam engines or dummies were operated with limited success1 and then only under exceptional conditions4 ,as a result1 practically every country of the world where the density of population and the state of civilization has warranted1 is traversed by a network of electric railways1 securing the most complete intercommunication between the various localities and handling local transportation in a manner impossible for a railway line employing steam locomotives4 ,the great advance in electric transportation1 aside from its meeting an economic need1 has been due to the development of systems of generating and transmitting power economically over long distances4 ,if water power is available1 turbines and electric generators can be installed and power produced and transmitted over long distances1 as1 for example1 from ,niagara ,falls to ,buffalo1 or even to much greater distances as in the case of power plants on the ,pacific coast where mountain streams and lakes are employed for this purpose with considerable efficiency4 ,a high tension alternating current thus can be transmitted over considerable distances and then transformed into direct current which flows along the trolley wires and is utilized in the motors4 ,this transformation is usually accomplished by means of a rotary converter1 that is1 an alternating current motor which carries with it the essential elements of a direct current dynamo and receiving the alternating current of high potential turns it out in the form of direct current at a1 lower and standard potential4 ,the alternating current at high potential can be transmitted over long distances with a minimum of loss1 while the direct current at lower potential is more suitable for the motor and can be used with greater advantage1 yet its potential or pressure decreases rapidly over long lengths of line1 so that it is more economical to use sub-stations to convert the alternating current from the power plant4 ,it must not be inferred1 however1 that all electric railways employ direct current machinery4 ,in ,europe alternating current has been used with great success and also in the ,united ,states where a number of lines have been equipped with this form of power4 ,but the greater number of installations employ the direct current at about #ejj-fjj volts and this is now the usual practice4 ,whether it will continue so in the future or not is perhaps an open question4 ,the electric car1 as we have seen1 employs a motor which is geared to the axle of the driving trucks1 and the current is derived from the trolley wire by the familiar pole and wheel and after flowing through the controller to the motor returns by the rail4 ,the speed of the car is regulated by the amount of current which the motorman allows to pass through the motor and the circuits through which it flows in order to produce different effects in the magnetic attraction of the magnet and the armature4 ,in the ordinary electric car for urban or suburban uses there has been a constant increase in the power of the motor and size of the cars1 as it has been found that even large cars can be handled with the required facility necessary in crowded streets and that they are correspondingly more economical to maintain and operate4 ,the success of electric traction in large cities had been demonstrated but a few years when it was appreciated that the overhead wires of the trolley were unsightly and dangerous1 especially in the case of fire or the breaking of the wires or supports4 ,accordingly a system was developed where the current was obtained from conductors laid in a conduit on insulated supports through a slot in the centre of the track between the rails4 ,a plow suspended from the bottom of the car was in contact with the conductors which were steel rails mounted on insulated supports1 and through them the current passed by suitable conductors to the controller and motors4 ,this system found an immediate vogue in ,american cities1 and though more costly to install than the overhead trolley1 was far more satisfactory in its results and appearance4 ,in certain cities1 ,washington1 ,d4 ,c41 for example1 the conduit is used in the built-up portion of the town and when the suburbs are reached the plow is removed and the motors are connected with the trolley wire by the usual pole and wheel4 ,perhaps the most important feature of the electric railway in the ,united ,states has been the development and increase of its efficiency4 ,wherever possible traffic conditions warranted1 it was comparatively easy to secure the right of way along country highways with little1 if any1 expense1 and the construction of track and poles for such work was not a particularly heavy outlay4 ,it was found1 as we have seen1 that the current could be transmitted over considerable distances so that the opportunity was afforded to supply transportation between two towns at some small distance where the local business at the time of the construction of the road would not warrant the outlay4 ,this led to the systems of interurban lines1 small at first1 but as their success was demonstrated1 gradually extending and uniting so that not only two important towns were connected1 but eventually a large territory was supplied with adequate transportation facilities and even mail1 express1 and light freight could be handled4 ,again the success of such enterprises made it feasible for the electric railways to forsake the public highway and to secure a right of way of their own1 and gradually to develop express and through service1 often in direct competition with the local service of the steam railways in the same territory4 ,here larger cars were required and power stations of the most modern and efficient type in order to secure proper economy of operation4 ,the general character of machinery1 both generators and motors1 was preserved even for these long distance lines1 and their operation became simply an engineering problem to secure the maximum efficiency with a minimum expenditure4 ,with the success of electric railways in cities and for suburban and interurban service naturally arose the question1 why electric power whose availability and economy had been shown in so many circumstances could not be used for the great trunk lines where steam locomotives have been developed and employed for so many years8 ,the question is not entirely one of engineering unless as part of the engineering problem we consider the various economic elements that enter into the question1 and their investigation is the important task of the twentieth century engineer4 ,for he must answer the question not only is a method possible mechanically1 but is it profitable from a practical and economic standpoint8 ,and it is here that the question of the electrification of trunk lines now rests4 ,the steam locomotive has been developed to a point perhaps of almost maximum efficiency where the greatest speed and power have been secured that are possible on machines limited by the standard gauge of the track1 #d feet #h #a_/b inches1 and the curves which present railway lines and conditions of construction demand4 ,now1 withal1 the steam locomotive mechanically considered is inefficient1 as it must take with it a large weight of fuel and water which must be transformed into steam under fixed conditions4 ,if for example1 we have one train a day working over a certain line1 there would be no question of the economy of a steam locomotive1 but with a number1 we are simply maintaining isolated units for the production of power which could be developed to far greater advantage in a central plant4 ,just as the factory is more economical than a number of workers engaged at their homes1 and the large establishment of the trust still more economical in production than a number of factories1 so the central power station producing electricity which can be transmitted along a line and used as required is obviously more advantageous than separate units producing power on the spot with various losses inherent in small machines4 ,but even if the central station is theoretically superior and more economical it does not imply that it is either good policy or economy to electrify at once all the trunk lines of a country such as the ,united ,states and to send to the scrap heap thousands of good locomotives at the sacrifice of millions of dollars and the outlay of millions more for electrical equipment4 ,in other words1 unless the financial returns will warrant it1 there is no good and positive reason for the electrification of our great trans- continental lines and even shorter railroads4 ,that is the situation to-day1 but to-morrow is another question1 and the far- seeing railroad man must be ready with his answer and with his preparations4 ,to-day terminal services in large cities can better be performed by electricity1 and not only is there economy in their operation1 but the absence of dirt1 smoke and noise is in accord with public sentiment if not positively demanded by statute or ordinance4 ,suburban service can be worked much more economically and effectively by trains of motor cars1 and time table and schedule are not limited by the number of available locomotives on a line so equipped4 ,on mountain grades1 where auxiliary power or engines of extreme capacity are required1 electricity generated by water power from melting snow or mountain lakes or streams in the vicinity may be availed of4 ,under such conditions powerful motors can be used on mountain divisions1 not only with economy1 but with increased comfort to passengers1 especially where there are long tunnels4 ,all this and more the railway man of to-day realizes1 and electrification to this extent has been accomplished or is in course of construction4 ,for each one of the services mentioned typical installations can be given as examples1 and to accomplish the various ends1 there is not only one system but several systems of electrical working1 which have been devised by electrical engineers to meet the difficulties4 ,to summarize then1 electric working of a trunk line results in increased economy over steam locomotives by concentration of the power and especially by the use of water power where possible4 ,thus economy is secured to the greatest extent by a complete electrical service and not by a mixed service of electric and steam locomotives4 ,electrification gives an increase in capacity both in the haulage by a locomotive1 an electric locomotive being capable of more work than a steam locomotive1 and in schedule and rate of speed1 as motor car trains and electric terminal facilities make possible augmented traffic1 and an increased use of dead parts of the system such as track and roadbed4 ,there is a great gain in time of acceleration and for stopping1 and for the ,boston terminal it was estimated that with electricity #ej per cent1 more traffic could be handled1 as the headway could be reduced from three to two minutes4 ,the modern tendency of electrification deals either with special conditions or where the traffic is comparatively dense4 ,from such a beginning it is inevitable that electric working should be extended and that is the tendency in all modern installations1 as for example1 at the ,new ,york terminal of the ,new ,york ,central and ,hudson ,river ,railroad where the electric zone1 first installed within little more than station limits1 is gradually being extended4 ,as examples of density of traffic suitable for electrification1 yet at the same time possessing problems of their own1 are the great terminals such as the ,grand ,central ,station of the ,new ,york ,central and ,hudson ,river ,railroad in ,new ,york ,city1 the new ,pennsylvania ,station in the same city1 and that of the ,illinois ,central ,station in the city of ,chicago4 ,not only is there density here but the varied character of the service rendered1 such as express1 local1 suburban1 and freight1 involves the prompt and efficient handling of trains and cars4 ,now1 with suburban trains made up of motor cars1 a certain number of locomotives otherwise employed are released2 for these cars can be operated or shifted by their own power4 ,such terminal stations are often combined with tunnel sections1 as in the case of the great ,pennsylvania terminal1 where the tunnel begins at ,bergen1 ,new ,jersey1 and extends under the ,hudson ,river1 beneath ,manhattan ,island and under the ,east ,river to ,long ,island ,city4 ,it is here that electric working is essential for the comfort of passengers as well as for efficient operation4 ,but there are tunnel sections not connected with such vast terminals1 as in the case of the ,st4 ,clair tunnel under the ,detroit ,river4 ,while the field and future direction of electrification is fairly well outlined and its future is assured1 yet this future will be one of steady progress rather than one of sudden upheaval for the economic reasons before stated4 ,to-day there are no final standards either of systems or of motors and the field is open for the final evolution of the most efficient methods4 ,notwithstanding the extraordinary progress that has been made many further developments are not only possible now but will be demanded with the progress of the art4 ,the great problem of the electric railway is the transmission of energy1 and while power may be economically generated at the central station1 yet1 as ,mr4 ,frank ,j4 ,sprague1 one of the pioneers and foremost workers in the electrical engineering of railways has so aptly said1 it is still at that central station and it will suffer a certain diminution in being carried to the point of utilization as well as in being transformed into power to move locomotives1 so that these two considerations lie at the bottom of the electric railway and on them depend the choice of the system and the design and construction of the motor4 ,the two fundamental systems for electric railways1 as in other power problems1 are the direct current and the alternating current4 ,in the former we have the familiar trolley wire1 fed perhaps by auxiliary conductors carried on the supporting poles or the underground trolley in the conduit1 or the third rail laid at the side of the track4 ,all of these have become standard practice and are operated at the usual voltage of from #ejj to #fjj volts4 ,the current on lines of any considerable length is alternating current1 supplied from large central generating stations and transformed to direct as occasion may demand at suitable sub-stations4 ,recently there has been a tendency to employ high voltage direct current systems where the advantages of the use of direct current motors are combined with the economies of high voltage transmission1 chief of which are the avoiding of power losses in transmission and the economy in the first cost of copper4 ,these high voltage direct current lines were first used in ,europe1 and during the year #aijg experimental lines on the ,vienna railway were tested4 ,,in ,germany and ,switzerland tests were made of direct current system of #b1jjj and #c1jjj volts and in #aijh there was completed the first section of a #a1bjj-volt direct current line between ,indianapolis and ,louisville1 which marked the first use of high tension direct current in the ,united ,states1 and this was followed by other successful installations4 ,with alternating current there can be used the various forms of single phase or polyphase current familiar in power work1 but the latter is now preferred1 and in ,europe and in the ,united ,states in the latter part of #aijh the number of single phase lines was estimated at #bg and #bh respectively1 with a total mileage of #ghb and #ifg miles4 ,a trolley wire or suspended conductor is used4 ,to employ a single phase current1 motors of either the repulsion type or of the series type are used and are of heavier weight than the direct current motors1 as they must combine the functions of a transformer and a motor4 ,it is for this reason that we often see two electric locomotives at the head of a single train on lines where the single phase system is employed1 while on neighboring lines using direct current1 one locomotive of hardly larger size suffices4 ,with the polyphase current a motor with a rotating field is used1 and they have considerable efficiency as regards weight when compared with the single phase and with the direct current motor4 ,the polyphase motor1 however1 is open to the objection that it does not lend itself to regulations as well as the direct current form1 and with ingenious devices involving the arrangement of the magnetic field and the combination of motors1 various running speeds can be had4 ,the usual voltage for these motors is #c1jjj volts1 but in the polyphase plant designed for the ,cascade ,tunnel #f1jjj volts are to be used4 ,they possess many advantages1 especially their ability to run at overload1 and consequently a locomotive with polyphase motor will run up grade without serious loss of speed4 ,the single phase system has been carried on on ,swiss and ,italian railroads1 notably on the ,simplon ,tunnel and the ,baltelina lines with great success1 and the distribution problems are reduced to a minimum4 ,in the ,united ,states a notable installation has been on the ,new ,york1 ,new ,haven ,hartford ,railroad1 where the section between ,stamford and ,new ,york has been worked by electricity exclusively since ,july #a1 #aijh4 ,here the single phase motors use direct current while running over the tracks of the ,new ,york ,central from ,woodlawn to the ,grand ,central ,terminal4 ,on both the ,new ,york1 ,new ,haven ,hartford and the ,new ,york ,central locomotives the armature is formed directly on the axle of the driving wheels1 so consequently much interest attaches to the new design adopted for the ,pennsylvania tunnels1 where the armatures of the direct current motors are connected with the driving wheels by connecting rods somewhat after the fashion of the steam locomotive1 and following in this respect some successful ,european practice4 ,,appendix4 ,,units ,,of ,,measurement4 7,from ,munro and ,jamieson's ,pocket-book of ,electrical ,rules and ,tables74 ,i4 ,,fundamental ,,units4--,the electrical units are derived from the following mechanical units3-- ,the ,centimetre as a unit of length2 ,the ,gramme as a unit of mass2 ,the ,second as a unit of time4 ,the ,centimetre is equal to #j4cicg inch in length1 and nominally represents one thousand-millionth part1 or #a_/a1jjj1jjj1jjj of a quadrant of the earth4 ,the ,gramme is equal to #ae4dcb grains1 and represents the mass of a cubic centimetre of water at #d degrees ,c4 ,mass is the quantity of matter in a body4 ,the ,second is the time of one swing of a pendulum making #hf1afd4ji swings in a sidereal day1 or #a_/hf1djj part of a mean solar day4 ,,ii4 ,,derived ,,mechanical ,,units4- ,area4-,the unit of area is the square centimetre4 ,volume4--,the unit of volume is the ,,cubic ,,centimetre4 ,,velocity is rate of change of position4 ,it involves the idea of direction as well as that of magnitude4 ,,velocity is ,,uniform when equal spaces are traversed in equal intervals of time ,the unit of velocity is the velocity of a body which moves through unit distance in unit time1 or the ,,velocity ,,of ,,one ,,centimetre ,,per ,,second4 ,,momentum is the quantity of motion in a body1 and is measured by mass x velocity4 ,,acceleration is the rate of change of velocity1 whether that change take place in the direction of motion or not4 ,the unit of acceleration is the acceleration of a body which undergoes unit change of velocity in unit time1 or an acceleration of one centimetre-per-second per second ,the acceleration due to gravity is considerably greater than this1 for the velocity imparted by gravity to falling bodies in one second is about #iha centimetres per second 7or about #cb4b feet per second74 ,the value differs slightly in different latitudes4 ,at ,greenwich the value of the acceleration due to gravity is g#iha4ag2 at the ,equator g#igh4a2 at the ,north ,pole g#ihc4a4 ,,force is that which tends to alter a body's natural state of rest or of uniform motion in a straight line4 ,,force is measured by the acceleration which it imparts to mass--i4 e41 mass x acceleration4 ,,the ,,unit ,,of ,,force1 or ,,dyne1 is that force which1 acting for one second on a mass of one gramme1 gives to it a velocity of one centimetre per second4 ,the force with which the earth attracts any mass is usually called the weight of that mass1 and its value obviously differs at different points of the earth's surface ,the force with which a body gravitates--i e1 its weight 7in dynes71 is found by multiplying its mass 7in grammes7 by the value of g at the particular place where the force is exerted4 ,work is the product of a force and a distance through which it acts4 ,the unit of work is the work done in overcoming unit force through unit distance--i e1 in pushing a body through a distance of one centimetre against a forch of one dyne4 ,it is called the ,erg4 ,since the weight of one gramme is #a ,x #iha or #iha dynes1 the work of raising one gramme through the height of one centimetre against the force of gravity is #iha ergs or g ergs4 ,one kilogramme-metre #ajj1jjj 7g7 ergs #i #h #a ,x #ajg ergs4 ,one foot- pound #ac1hbe 7g7 ergs1 #a #cef ,x #ajg ergs4 ,energy is that property which1 possessed by a body1 gives it the capability of doing work4 ,kinetic energy is the work a body can do in virtue of its motion4 ,potential energy is the work a body can do in virtue of its position4 ,the unit of energy is the ,erg4 ,power or ,activity is the rate of work2 the practical unit is called the ,watt--#ajg ergs per second4 ,a ,horse-power #cc1jjj ft--,ibs per minute #eej ft--,ibs per second1 but as seen above under ,work1 #a ft--,ib #a #cef ,x #ajg ergs1 and under ,power1 #a ,watt #ajg ergs per sec a ,horsepower #eej ,x #a #cef ,x #ajg ergs #gdf ,watts2 or1 ,,ec_/#gdf;,c#b,r_/#gdf;,e#b_/7gdf ,r7 ,,hp where ,e volts1 ,c amperes1 and ,r ohms4 ,the ,french force de cheval #ge kilogramme metres per sec #gcf ,watts #edb #dh ft--lbs4 per sec4 4#ihfc ,h4,p42 or one ,h4,p4 #a4jache force de cheval4 ,,derived ,,electrical ,,units4--,there are two systems of electrical units derived from the fundamental ,c4,g4,s4 units1 one set being based upon the force exerted between two quantities of electricity1 and the other upon the force exerted between two magnetic poles4 ,the former set are termed electro-static units1 the latter electro-magnetic units4 ,,iii4 ,,electrostatic ,,units4-- ,,unit ,,quantity of electricity is that which repels an equal and similar quantity at unit distance with unit force in air4 ,,unit ,,current is that which conveys unit quantity of electricity along a conductor in a second4 ,,unit ,,electromotive ,,force1 or unit ,,difference ,,of ,,potential exists between two points when the unit quantity of electricity in passing from one to the other will do the unit amount of work4 ,,unit ,,resistance is that of a conductor through which unit electromotive force between its ends can send a unit current4 ,,unit ,,capacity is that of a condenser which contains unit quantity when charged to unit difference of potential4 ,,iv4 ,,magnetic ,,units4-- ,,unit ,,magnetic ,,pole is that which repels an equal and similar pole at unit distance with unit force in air4 ,,strength ,,of ,,magnetic ,,field at any point is measured by the force which would act on a unit magnetic pole placed at that point4 ,,unit ,,intensity ,,of ,,field is that intensity of field which acts on a unit pole with unit force4 ,,moment ,,of ,a ,,magnet is the strength of either pole multiplied by the distance between the poles4 ,,intensity ,,of ,,magnetisation is the magnetic moment of a magnet divided by its volume4 ,,magnetic ,,potential4--,the potential at a point due to a magnet is the work that must be done in removing a unit pole from that point to an infinite distance against the magnetic attraction1 or in bringing up a unit pole from an infinite distance to that point against the magnetic repulsion4 ,,unit ,,difference ,,of ,,magnetic ,,potential4--,unit difference of magnetic potential exists between two points when it requires the expenditure of one erg of work to bring an 7,n4 or ,s47 unit magnetic pole from one point to the other against the magnetic forces4 ,v4 ,,electro-,,magnetic ,,units4-- ,,unit ,,current is that which in a wire of unit length1 bent so as to form an arc of a circle of unit radius1 would act upon a unit pole at the centre of the circle with unit force4 ,,unit ,,quantity of electricity is that which a unit current conveys in unit time4 ,,unit ,,electro-,,motive ,,force or ,,difference ,,of ,,potential is that which is produced in a conductor moving through a magnetic field at such a rate as to cut one unit line per second4 ,,unit ,,resistance is that of a conductor in which unit current is produced by unit electro-motive force between its ends4 ,,unit ,,capacity is that of a condenser which will be at unit difference of potential when charged with unit quantity4 ,electric and magnetic force varies inversely as the square of the distance4 ,,practical ,,units ,,of ,,electricity4 ,,resistance-,r4--,the ,ohm is the resistance of a column of mercury #ajf4c centimetres long1 #a square millimetre in cross-section1 weighing #ad4deba grammes1 and at a temperature of #j degrees centigrade4 ,standards of wire are used for practical purposes4 ,the ohm is equal to a thousand million1 #aji1 electromagnetic or ,centimetre-,gramme-,second 7,c4 ,g4 ,s47 units of resistance4 ,the megohm is one million ohms4 ,the microhm is one millionth of an ohm4 ,,electromotive ,,force--,e4--,the ,volt is that electromotive force which maintains a current of one ampere in a conductor having a resistance of one ohm4 ,the electromotive force of a ,clark standard cell at a temperature of #ae degrees centigrade is #a4dcd volts4 ,the volt is equal to a hundred million1 #ajh1 ,c4 ,g4 ,s4 units of electromotive force4 ,,current--,c4--,the ,ampere is that current which will decompose #j4jicbd milligramme of water 7,h#b,o7 per second or deposit #a4aah milligrammes of silver per second4 ,it is equal to one-tenth of a ,c4 ,g4 ,s4 unit of current4 ,the milliampere is one thousandth of an ampere4 ,,quantity--,q4--,the ,coulomb is the quantity of electricity conveyed by an ampere in a second4 ,it is equal to one-tenth of a ,c4 ,g4 ,s4 unit of quantity4 ,the micro-coulomb is one millionth of a coulomb4 ,,capacity--,k4--,the farad is that capacity of a body1 say a ,leyden jar or condenser1 which a coulomb of electricity will charge to the potential of a volt4 ,it is equal to one thousand-millionth of a ,c4 ,g4 ,s4 unit of capacity4 ,the micro-farad is one millionth of a ,farad4 ,by ,ohm's ,law1 ,current ,electromotive ,force_/ ,resistance1 or ,c ,e_/,r ,ampere ,volt_/,ohm ,hence when we know any two of these quantities1 we can find the third4 ,for example1 if we know the electromotive force or difference of potential in volts and the resistance in ohms of an electric circuit1 we can easily find the current in amperes4 ,,power--,p4--,the ,watt is the power conveyed by a current of one ampere through a conductor whose ends differ in potential by one volt1 or1 in other words1 the rate of doing work when an ampere passes through an ohm4 ,it is equal to ten million1 #ajg1 ,c4 ,g4 ,s4 units of power or ergs per second1 that is to say1 to a ,joule per second1 or #a_/gdf of a horse-power4 ,a ,watt volt ,x ampere1 and a ,horse-power ,watts_/#gdf4 ,,heat ,,or ,,work--,w4--,the ,joule is the work done or heat generated by a ,watt in a second1 that is1 the work done or heat generated in a second by an ampere flowing through the resistance of an ohm4 ,it is equal to ten million1 #ajg1 ,c4 ,g4 ,s4 units of work or ergs4 ,assuming ,joule's equivalent of heat and mechanical energy to be #da1fjj1jjj1 it is the heat required to raise 4#bd gramme of water #a degrees centigrade4 ,a ,joule ,volt x ampere x second4 ,since #a horse-power #eej foot pounds of work per second1 ,w #eej_/gdf ,e4 ,q4 4#gcgc ,e4 ,q4 foot pounds4 ,,heat ,,units4 ,the ,british ,unit is the amount of heat required to raise one pound of water from #fj degrees to #fa degrees ,fahrenheit4 ,it is #bea4i times greater than the metric unit1 therm or calorie1 which is the amount of heat required to raise one gramme of water from #d degrees to #e degrees centigrade4 ,joule's ,equivalent--,j4--is the amount of energy equivalent to a therm or calorie1 the metric unit of heat4 ,it is equal to #da1fjj1jjj ergs4 ,the heat in therms generated in a wire by a current ,volt ,x ampere ,x time in seconds ,x #j4bd4 ,,light ,,units ,the ,british ,unit is the light of a spermaceti candle #g_/h-;inch in diameter1 burning #abj grains per hour 7six candles to the pound74 ,they sometimes vary as much as #aj per cent1 from the standard4 ,mr4 ,vernon ,harcourt's standard flame is equal to an average standard candle4 ,the ,french ,unit is the light of a ,carcel lamp1 and is equivalent to #i ,t_/,z ,british units4