,,the ,,magic ,,lantern ,,and ,,its ,,management4 ,,the ,,magic ,,lantern ,,and ,,its ,,management ,,including ,,full ,,practical ,,directions ,,for ,,producing ,,the ,,lime ,,light1 ,,making ,,oxygen ,,gas1 ,,and ,,preparing ,,lantern ,,slides ,,by ,t4 ,c4 ,,hepworth ,,late ,,lecturer ,,on ,,science ,,to ,,the ,,royal ,,polytechnic ,,institution1 ,,london4 ,illustration ,london ,,chatto ,,and ,,windus1 ,,piccadilly #ahhe ,all rights reserved ,,preface4 ,during the past few years1 the introduction of a dry-plate photographic process of such a nature that it can be practised successfully by amateurs of both sexes has aroused an amount of interest in the camera and its capabilities1 such as few scientific instruments can command4 ,the ,magic ,lantern is now closely allied with the camera1 for there is no means of showing the perfection of a photographic picture so well as by its aid4 ,but many persons are deterred from adopting the latter contrivance because they fancy that there must be innumerable difficulties to surmount before they can hope to master its management4 ,it is for these that the following pages have been written1 in which ,i have tried to place clearly before the reader what can be done1 and how to do it4 ,i have also tried to indicate the educational value of the lantern1 and have pointed out in a necessarily brief manner how various branches of knowledge can be illustrated by its aid4 ,the numerous personal inquiries addressed to me after my lectures1 and the numbers of letters constantly received1 asking for information regarding the lantern1 its management1 and the preparation of lantern slides1 have convinced me that there is room for a manual1 humble though it be1 dealing with these subjects4 ,t4 ,c4 ,,hepworth4 #cb1 ,,cantlowes ,,road1 ,,london1 ,n4,w4 ,,contents4 ,,the ,,history ,,of ,,the ,,magic ,,lantern4 ,,page ,the introduction of mineral oil lanterns4--,the advance caused by the aid of photography4--,the optical system of a modern lantern4--,educational value of the lantern #a-ab ,,the ,,lime-,,light4 ,different forms of lime-jets4--,precautions to be observed in their use #ab-af ,,dissolving ,,views4 ,the old method and the new4--,the biunial lantern4--,the dissolving-tap and its management4--,coincident discs4--#8,effects'--,the application of the double lantern to spectrum analysis #ag-bb ,,making ,,oxygen ,,gas4 ,necessary precautions4--,the purifier4--,explanatory diagram4--,practical details4--,the retort4--,the gas-bag4--,iron bottle for compressed gas4--,pressure-boards4 --,lime cylinders #bb-cc ,,the ,,screen ,,or ,,sheet4 ,arrangement adapted to a sitting-room4--,public exhibitions4 --,method of hanging a large sheet4--,sheets on frames #cc-cg ,,pictures ,,for ,,the ,,lantern4 ,photographic slides4--,home-made pictures4--,drawing pictures on ground-glass4--,the slide-painter's easel4--,mounting slides #cg-dc ,,on ,,the ,,colouring ,,of ,,photographic ,,transparencies4 ,the process described4--,oil-colours employed4--,apparatus required4--,mixed tints4--,how to lay on the colour4--,finishing touches4--,painting in water-colours #dc-ee ,,showing ,,solid ,,and ,,opaque ,,objects ,,on ,,the ,,lantern ,,screen4 ,chadburn's opaque lantern4--,the aphengescope4--,showing coins1 medals1 etc4--,the opaque lantern in a law court4--,the physioscope #ef-fa ,,the ,,lantern ,,microscope4 ,photographic microscopic slides4--,the solar microscope4--,a sketch lecture #fa-fe ,,mechanical ,,or ,,moving ,,pictures4 ,comic slips4'--,beale's choreutoscope4--,the dancing skeleton #ff-fi ,,concluding ,,remarks4 ,the management of the lantern in public4--,signals between lecturer and operator #gj-ge ,,the ,,magic ,,lantern ,,and ,,its ,,management4 ,there is no optical instrument so well known or so highly held in popular estimation as the ,magic ,lantern4 ,it is somewhat unfortunate that its old appellation1 given to it when it was nothing more than a mere toy1 should have stuck to it so long4 ,and more than one attempt has been made by those conversant with its capabilities as a scientific instrument1 and as an important aid to education1 to give it a name more consistent with its real value4 ,the late ,mr4 ,dalmeyer was1 ,i believe1 the first to re-christen it the #8,optical ,lantern2' and there is evidence that others are adopting the term1 and that in time the old name will sink into oblivion4 ,with regard to the early history of this deservedly favourite contrivance1 but little is known4 ,its invention has been ascribed to ,friar ,bacon1 but the evidence on this point is of the most legendary character4 ,it seems1 however1 certain that the first to give an intelligent description of it was ,kircher--a ,jesuit who lived two and a half centuries ago1 and who published a work entitled #8,ars ,magna ,lucis et ,umbr1' or #8,the ,great ,art of ,light and ,shadow4' ,the body of the lantern1 as described by ,kircher1 consisted of a room several feet across1 furnished with an opening in which a lens was placed4 ,the source of light was an oil-lamp1 and the pictures for exhibition were of the roughest kind4 ,indeed1 we may presume that the effects produced fell far short of those attained by the cheapest toy lantern of our schoolboy days4 ,even if we search the columns of an ,encyclopdia or any similar book of reference of forty years ago1 we shall not find any great improvement on the description afforded by ,kircher4 ,the magic lantern will there be found described as #8an optical toy1 by which glass pictures executed with coloured varnishes can be thrown upon a wall or screen4' ,but from this time a gradual improvement began4 ,first1 the old oil-lamp was replaced by the argand burner2 then came gas2 finally the brilliant lime-light--and some time in the near future1 perhaps1 will come electricity4 ,the improved means of obtaining light have naturally led to larger pictures being thrown on the screen2 for the size of such pictures is governed only by the amount of light available4 ,thus1 supposing we own a modern lantern constructed with one of the improved three or four-wick lamps1 and that it will give us a good picture of about six feet diameter1 by using the same lantern1 and without any change whatever in its optical arrangements1 save fitting it with a lime-light jet1 the disc can be increased to fifteen feet diameter4 ,a picture of the same size could be produced with the original lamp1 provided that the operator retired to the necessary distance from the screen1 but the light would be so attenuated that the picture would be but a ghost of what it ought to be4 ,it will therefore be understood that the enlarged image formed by the lantern lens can be made to fall at any point in front of that lens1 and may be of any size2 but to render it practically available its size1 and therefore its distance from the lens1 must be regulated by the amount of light at disposal4 ,during the past few years two circumstances have combined to render the optical lantern more popular than ever3 one being the introduction of photographic transparencies representing scenes from the remotest parts of the earth1 and the other the construction of metal-bodied lanterns of improved character1 and burning mineral oil4 ,as a good paraffine lamp is compared with a farthing rushlight1 so is one of these lanterns to the toy of our boyhood4 ,the light given1 although it falls far short of the brilliance of the lime-light1 is much more intense than could have been hoped for some years ago from oil4 ,but its brilliance is not all due to the paraffine1 but quite as much to the careful ventilation and general construction of the flame-chamber4 ,there is1 too1 no danger in the use of this form of lantern1 for the reservoir containing the paraffine is far below the combustion-chamber1 and therefore it cannot become unduly heated4 ,the lenses1 too1 in this new form of lantern1 although placed in the same position as those in the old-fashioned magic lantern1 are of a very different stamp4 ,and this leads me to a brief consideration of the optical system comprised in these instruments4 ,illustration3 ,,fig4 #a4 ,l1 ,light2 c1 c1 ,condensing lenses2 o1 o1 ,objective lenses4 ,there are two sets of lenses3 one being known as the condenser1 and the other as the objective4 ,the condenser is made up of two or more glasses1 the usual form consisting of two plano-convex lenses placed face to face4 ,the duty of this condenser is to take up as much as possible of the light afforded by the lamp1 and to change the direction of the rays so that they are cast through the picture or slide placed in front of it4 ,a glance at ,fig4 #a4 will show how this is accomplished1 and how the rays indicated by the dotted lines would be lost if not turned to account by the condenser4 ,the use of the objective1 on the other hand1 is to magnify the image of the picture1 and to present it in as perfect a form as possible on the screen placed for its reception4 ,its distance from the picture is governed by the distance of the lantern from the screen1 and can be regulated to a nicety by the focusing screw attached to it4 ,it is generally acknowledged by all acquainted with the requirements of the lantern that the photographic camera lens 7known as the quarter-plate portrait lens7 fulfils admirably this duty2 and this particular form of lens1 which is by no means expensive1 is generally fitted to modern lanterns of the mineral-oil type4 ,the condensers vary from four to three inches in diameter2 perhaps the best size is three and a half inches4 ,the relative positions of condenser1 light1 slide1 and objective are indicated in the diagram to which attention has just been called1 ,fig4 #a4 ,the optical lantern always inverts the image of any picture projected by it1 an inconvenience readily obviated by placing the slide on the stage upside down4 ,at the same time the picture must have its front turned towards the condenser1 not away from it1 otherwise every part of the slide suffers reversal on the screen4 ,in some cases this does not matter1 but when any wording1 such as that on a signboard1 for instance1 is contained in the picture1 it reads backwards4 ,such accidents can be prevented by a white label1 easily seen in semi-darkness1 placed in a certain position on the picture4 ,if such a precaution had been observed at a certain exhibition at which ,i was present1 ,general ,garfield would not have been shown standing on his head--not a dignified position for the ,president of the ,american ,republic4 ,the first lanterns1 constructed to burn mineral oils1 were very different to those of modern make1 and took their pattern from the cumbrous instruments which before them were provided with colza-oil lamps4 ,the reservoir for the oil was carefully kept in a cistern at the back of the lantern1 and bubbled through a pipe to the lamp on the same principle that water is supplied to an earthenware poultry fountain4 ,it was doubtless thought necessary in those days to maintain the paraffine in the cistern at a height equal to or above the wick1 as in the case of colza and other heavy oils4 ,but paraffine is more of the nature of a spirit--for it volatilizes very readily--and in modern lamps for lanterns the reservoir is kept some inches below the point of combustion4 ,by the time that the liquid reaches this point1 it has become so heated in the course of its passage along the metal wick-holders that it issues as a gas4 ,this can be readily proved by turning down the wicks after the lantern has been burning some time1 when the flames will remain above the wick-holders1 although the wicks themselves have been turned down quite out of reach4 ,in the older lanterns1 too1 the glass chimney was thought to be indispensable1 but now this has been done away with1 and with it the cylindrical wick has also gone4 ,the modern combustion-chamber is made of charcoal iron1 and is closed at one end with a thin pane of glass1 just outside which the condensing lenses are placed1 and at the other end by a silver-plated reflector4 ,the necessary air to promote combustion is admitted by suitable orifices below1 and a draught is established by a long iron chimney above4 ,there is no great difficulty in managing one of these lanterns4 ,the loosely plaited cotton wicks should in the first instance be carefully cut parallel with the wick-holders4 ,after this they do not require much attention4 ,it is a far better plan to remove the charred end of the wicks by scraping them along with the back of a knife1 than to be always cutting them afresh4 ,however1 any loose strands that may project from the cotton should be certainly snipped off with scissors4 ,after lighting the lantern--which is best done with a long wax taper--each wick should be turned down quite low1 and the combustion-chamber closed4 ,in about two minutes1 by which time the front glass and the lantern generally will have become warmed1 the wicks should be turned up to their highest2 that is to say1 to a pitch just short of smoking-point4 ,if the wicks are turned low for any length of time the lamp will be sure to smell4 ,it will also smell if1 in the process of charging with oil1 some of the liquid has been smeared against any part of the lantern which may afterwards become heated4 ,the best oil only should be used4 ,i have already hinted at the educational value of the optical lantern1 but those who have not experimented with it have but a faint idea of its capabilities in this respect4 ,i am of the opinion that every school and college should possess one1 and that both pupils and teachers would soon discover its many advantages4 ,now that it is manufactured in such a portable and efficient form1 and can be so easily managed1 there is no possible hindrance to its adoption1 unless it be its old name of #8magic lantern1' which is associated with things too childish for consideration4 ,but this objection cannot hold good when it is pointed out how many different branches of knowledge can be illustrated by its use4 ,the schoolmaster of a ,london ,board ,school once told me of some of his difficulties in teaching such a subject as geography4 ,most of the children had never seen the sea1 and many of them had never even travelled so far as the ,thames4 ,what notion could such waifs have of a mountain1 a valley1 a cliff1 or even of a rock8 ,the value of the optical lantern at once becomes apparent here4 ,but better informed children in high-class schools1 although they see many places beyond the ,london streets1 can yet reap much advantage from the mode of instruction which ,i am advocating2 and as the range of knowledge increases1 so will some such means of illustration be forced upon teachers4 ,the labour and expense of tracing a dozen diagrams on glass1 in the way hereafter explained1 is considerably less than that involved in drawing a single large diagram for the schoolroom wall4 ,by this easy method the illustrations in any book can be roughly copied and rendered available for an entire class4 ,in the higher branches of knowledge the lantern can also give its help4 ,botany1 zoology1 and natural history generally can be illustrated by diagrams1 photographs1 and in many cases by natural preparations4 ,the revelations of the microscope can be transferred to the lantern1 and the most complex organisms can be seen clearly defined and magnified many hundred times their natural size4 ,it is possible1 too1 to show by the lantern many interesting experiments in chemistry and electricity which cannot be shown to a large number of persons in any other way4 ,let me cite for instance the formation of crystals1 which can actually be watched in progress1 highly magnified1 by the simple expedient of smearing a piece of glass with a solution of sal ammoniac and placing it in the lantern4 ,there are several adjuncts which may be fitted to a first-class lantern which ,i have not space to notice in detail4 ,with the lantern-microscope ordinary microscopic slides can be utilized1 and tanks for containing the living denizens of our ponds and ditches may be employed4 ,the marvels of polarised light may be demonstrated with the lantern-polariscope4 ,by another special device called the #8aphengescope' and which is made to fit on the lantern1 opaque objects can be thrown on the screen4 ,it is possible1 for instance1 to utilize ordinary photographs or diagrams on card1 to show the moving works of a watch1 sections of fruit1 and many other objects as explained in a subsequent chapter4 ,the lantern1 at the time of exhibition1 should stand firmly4 ,it can1 if it be a small one burning oil1 be placed on a box standing upon a table4 ,i myself prefer to place it on a photographic tripod-stand1 and this ,i effect by screwing on to the top of the stand a base-board upon which the lantern firmly fits4 ,for large lanterns1 such as the lime-light biunial1 a far more solid arrangement is requisite4 ,my own method is this4 ,the lantern screws on to the top of its travelling-box1 at the lower corners of which are sockets to admit four wrought-iron legs4 ,these legs are bent outwards1 and what ,i may call their toes are turned out1 and have a hole into which a screw may be inserted and driven into the floor4 ,the lantern is fastened to the box by two hinged pieces at the back1 so that the nozzles can be raised to any extent desired4 ,,the ,,lime-,,light4 ,the lime-light consists of a jet of mixed hydrogen and oxygen gases under pressure1 ignited1 and forced upon a cylinder of lime1 which it renders white-hot4 ,the heat given by these gases is second only to the heat of the electric arc1 and will melt that most refractory of metals1 platinum4 ,even the lime block cannot withstand the great heat to which it is exposed1 but is quickly pitted under the action of the flame4 ,hence lime-light jets are furnished with an arrangement by which the lime cylinder can be turned at frequent intervals1 so as to offer a fresh surface for the gases to play upon4 ,there are three kinds of jet used for the lantern4 ,firstly1 a jet in which a stream of oxygen is forced through the flame of a spirit-lamp on to a cylinder of lime4 ,this form is perfectly safe1 and although it presents an immense improvement upon any form of oil arrangement1 does not afford sufficient light to illuminate a screen more than about nine feet in diameter4 ,secondly1 there is what is known as the blow-through jet4 ,in this case the jet is connected with the house gas1 and the oxygen meets it at the point of ignition1 and is blown through it on to the lime4 ,this form of jet is also safe2 indeed1 it is often called #8the safety jet1' and affords plenty of light even for professional use4 ,it is the one that ,i recommend the amateur to work with4 ,thirdly1 there is the mixed jet1 in which the two gases in separate bags are both under pressure1 and mix together before reaching the external orifice4 ,this form of lime-light gives the most light of any2 but such care is requisite in dealing with it1 that ,i shall say no more about it1 considering it unfit for casual acquaintance4 ,a beginner might fancy that it would be a simple thing to mix the two gases in one bag1 put it under pressure1 and use them thus4 ,so it would1 and a beautiful light would be the result4 ,probably a beautiful explosion would be another result1 for the two gases mixed form a most terrible compound1 and a bag so charged would be almost equal in danger to a live shell4 ,with the spirit jet1 or the #8blow-through1' the operator need have no fear of danger4 ,oxygen is not an explosive1 and1 although the best supporter of combustion1 is not itself capable of being ignited4 ,the spirit jet ,i should not recommend1 except in situations where coal gas is not obtainable1 so in my directions for using the lime-light1 let it be understood that ,i am considering the employment of the blow-through1 or safety jet4 ,let us suppose1 then1 that we are preparing for an exhibition4 ,the gas is made1 and is at hand in the gas-bag2 our lantern--and ,i will1 for simplicity's sake1 consider it a single lantern only--is raised on its stand-table1 or other support1 at a convenient height from the ground1 and we wish to have a private rehearsal in order to see that all is right4 ,the first thing is to attach the hydrogen terminal of the jet1 marked ,h1 by flexible tubing to the nearest gas-bracket4 ,now take a cylinder of lime from its box1 clear out the hole in the centre with a bit of wire1 or a match1 and place it on the pin provided for it above the jet4 ,see that it turns freely1 and so adjust the pin that the lime is distant from the jet nozzle about the sixteenth of an inch4 ,light the gas1 and turn it down so that the flame is about an inch high4 ,this can be done with advantage an hour or more before the lantern is really required1 for the lenses and body of the lantern will by this means get thoroughly warmed1 and any moisture upon the glasses1 which would show as a blemish on the sheet1 will be removed4 ,in all cases the hydrogen should be lighted first1 if only to thoroughly warm the lime4 ,now the oxygen-bag can be put between the pressure-boards1 and connected by another tube to the tap marked ,o4 ,a half-hundred-weight having been put on the boards1 the gas-bag tap may be turned on to the full4 ,we may now attend to the jet4 ,turn on the hydrogen so that it flames up some inches over the lime1 then gradually turn on the oxygen4 ,at first it is air only that comes away1 but presently with a characteristic little snap the two gases come together1 and the brilliant lime-light is produced4 ,a little care in adjustment of each tap alternately will soon show us the amount of gas from each which will give the best result4 ,it will soon be apparent to the operator that the spot of light on the lime must be exactly in the axis of the system of lenses1 or the effect upon the sheet will be spoiled4 ,the vertical movement of the jet is governed by a little screw1 which holds it to the post on which it is fixed1 which post stands upon an iron tray gliding between grooves4 ,we must raise or lower the jet until the right place is found1 when the screw can be brought home1 and the jet is fixed4 ,even now1 most probably1 we shall find that the outer margin of the disc is ill-defined4 ,this shows that the light is either too near or too far from the condenser4 ,by moving the jet on its tray bodily backwards and forwards1 we shall soon be able to find its correct position1 and when found1 that position will hold good to the end of the exhibition4 ,we can now put a picture on the slide-stage1 and focus it by means of the screw on the front lens4 ,if the lime is properly adjusted and centred1 our picture will be illuminated equally well in every part4 ,,dissolving ,,views4 ,so far1 we have considered the production of a brilliantly illuminated picture with a single lantern4 ,for many years after the lime-light came into use1 this was all that was required of it4 ,but suddenly the beautiful effect known as dissolving views was contrived--an effect which1 at the time of its introduction1 made a wonderful sensation--and the method of producing which was for a long time kept secret4 ,the old way of dissolving one picture into another1 and the way which must still be adopted if oil-lanterns are in question1 was to use two lanterns1 side by side1 and by a kind of see-saw arrangement in front of the lenses1 to gradually uncover one nozzle whilst the other was being closed4 ,this was easily done by furnishing each end of the see-saw with a screen of tin1 the edge of each being cut into teeth like a comb4 ,the one picture was thus caused to mingle with the other until the first lantern was quite closed1 when the new design became perfectly disclosed4 ,it soon became evident that the same effect could be produced more simply and economically with the lime-light lanterns1 by contriving a special form of gas-tap which would slowly turn off the gases supplied to one lantern1 while it as slowly admitted the gases to the other4 ,by this arrangement nearly half the gas supply is saved1 and therefore very little more is wanted for a dissolving-view apparatus than for a single lantern4 ,dissolving view1 or biunial lanterns1 as they are generally termed1 are now made in very compact form4 ,the two systems of lenses1 one above the other--not side by side as of old--are fitted into one mahogany case1 lined with tin1 and furnished with doors1 so that the lights can be tended when necessary4 ,at the back of the arrangement is placed the dissolving-tap1 which is connected by indiarubber tubing with the lime-jets1 and has two nozzles by which the hydrogen and oxygen respectively can be supplied to it4 ,the dissolver is also furnished with by-passes1 so that when the gases are turned from one lantern1 just sufficient remains to keep the jet turned down #8to the blue4' ,the management of a pair of lanterns like this is1 of course1 much more onerous than that of a single lantern2 but when once understood presents no difficulty4 ,before lighting up1 be quite sure that all connections--and there are many--are quite secure1 and that each place where indiarubber tubing fits on to metal is secured with twine4 ,now light the hydrogen in both lanterns1 which you can do by placing the dissolving-tap in an upright position4 ,move the dissolver until the upper jet seems on the point of going out2 but prevent it doing so by opening the hydrogen by-pass1 and adjust this little tap so that the flame remains about one inch high when the other lantern is being used4 ,move the dissolver backwards and forwards a few times1 so as to see that it works well1 and that the hydrogen flares up in each lantern alternately4 ,we can now pay attention to the oxygen supply4 ,first see that the bag is properly adjusted between the pressure-boards1 and that the weight--one #ef lb4 weight is sufficient to begin with--is in its place1 above the upper board4 ,attending to the lower lantern first1 turn up the hydrogen1 and very gently admit the oxygen by turning the tap attached to the jet4 ,when the light has been satisfactorily established1 the oxygen by-pass must be turned in the same way that the other by-pass was just now treated1 so as to admit a small amount of gas passing to the lantern not in use4 ,if this be not done1 the sudden inrush of the oxygen is sure to cause a small explosion1 which will blow the light out4 ,this does not indicate any danger whatever1 but is inconvenient and undesirable during an exhibition4 ,the upper lantern may now be attended to with the same precautions2 and if all has been done well1 the light will move from jet to jet alternately1 as the dissolver is worked4 ,in using a double lantern1 it is necessary to make both pictures coincident on the sheet4 ,if one picture overlaps the other at every change1 it has a most slovenly appearance4 ,such an error can be avoided by manipulating certain screws fitted to the metal front of the lantern1 by which the two discs thrown upon the sheet can be adjusted until they quite coincide4 ,these screws allow the lower nozzle to be pointed slightly upwards1 and the upper one to point downwards1 so that the images cast by each may be made to meet at the screen4 ,the double lantern is mainly employed for dissolving views2 but its use does not stop here4 ,a great many beautiful 8effects0 can be compassed by its means1 a few of which ,i may here describe4 ,statuary slides form very beautiful pictures if photographed direct from the marble2 but their effect is much enhanced if1 by means of the auxiliary lantern1 a glow of colour is thrown upon the screen at the same time4 ,a few squares of differently tinted glasses1 each mounted like an ordinary slide1 with a mask of oval or round shape1 are all that is needed4 ,again1 a wintry scene in one lantern may be much improved by the effect of falling snow1 produced by working a special form of slide in the other lantern4 ,this slide consists merely of a frame containing a roller at the top with the handle projecting outside4 ,as the handle is rotated1 a long ribbon of black paper pierced with needle-pricks is rolled up upon it1 and each prick makes a descending spot of light upon the screen1 which together look exactly like falling snow4 ,sunset and moonlight effects1 windows lighted up in night-scenes1 ripples upon water1 can all be managed by specially-devised #8effect' slides in the second lantern4 ,these effects can be much extended when a triple lantern is employed2 but as this instrument is not often found--out of the hands of professional operators--we need not further allude to it4 ,but the double lantern can be used with great advantage from an educational point of view1 in a manner that was first suggested by the present writer4 ,i mean in the demonstration of the main features of ,spectrum ,analysis4 ,let me cite one example4 ,a slide prepared and coloured so as to represent the continuous solar spectrum1 marked with the principal ,frauenhofer lines1 is placed1 say1 in the lower lantern4 ,we now wish to show the bright lines given by an incandescent metal1 say sodium4 ,a slide1 all blackened out but the double ,d line due to sodium1 and so placed on the glass that it will exactly register with the ,d line in the coloured spectrum slide1 is placed in the upper lantern4 ,the dissolver is now brought into play1 and can be so adjusted that while the continuous spectrum has all but faded away1 the two brilliant sodium lines stand out boldly in their proper place4 ,the spectra of all the other metals can be treated in exactly the same manner1 keeping the continuous spectrum in the lower lantern for constant comparison and reference4 ,,making ,,oxygen ,,gas4 ,there is very little danger incurred in the use of the lime-light if only the operator be intelligent in its employment4 ,but there are certain dangers connected with the preliminary making of the oxygen gas1 so that that part of the work should only be entrusted to a careful worker1 and one who1 knowing where the greatest care is required1 will take every precaution against disaster4 ,i have myself made several thousand feet of oxygen on different occasions1 and have never yet met with any mishap2 but as ,i know of cases where serious accidents have occurred1 ,i have endeavoured to find out why they have happened1 and ,i now consider myself forewarned1 and therefore forearmed1 against their repetition4 ,the articles required for making the gas comprise a retort in which to generate it1 a gas-stove to furnish the necessary heat1 a wash-bottle or purifier1 an indiarubber gas-bag1 and several feet of tubing4 ,beyond these is wanted the mixture of chlorate of potash and peroxide of manganese in powder1 which forms the charge of the retort1 from which the gas is generated on the application of heat4 ,i have found that the best proportions of chemicals to use are four parts 7by weight7 of chlorate to one of manganese4 ,before being mixed together1 both should be most carefully picked over1 and most probably both will yield a small crop of bits of straw and wood-chips1 which are not only injurious1 but would in sufficient quantity prove actually dangerous if permitted to remain4 ,the larger crystals of the chlorate1 and any lumps which may be found in the manganese1 should be rubbed down to powder by gentle pressure with the wooden spoon used for mixing the compound1 about two pounds of which will yield sufficient gas for an evening's show4 ,the mixture can now be funnelled into the retort1 the nozzle of which1 after being blown through to see that the passage is clear1 can be screwed into its place4 ,the purifier1 or wash-bottle1 is made of tin1 or may consist of a wide-mouthed bottle with an indiarubber cap1 fitted with inlet and outlet tubes of metal or glass4 ,in either case the vessel is three-parts filled with water1 the inlet tube dipping some inches below the surface4 ,this tube is subsequently connected by three or four feet of indiarubber tubing with the retort4 ,as the gas is given off1 it bubbles through this water1 which not only cools it1 but catches the particles of solid matter which are sure to be blown from the retort4 ,the outlet tube is connected with the gas-bag4 ,in the annexed illustration the relative positions of the retort1 purifier1 and gas-bag are shown1 but in practice certain modifications are desirable4 ,it is as well1 for instance1 to stand a chair between the retort and purifier1 upon which the connecting rubber tube may rest1 otherwise the water evolved from the crystals of potash will condense in the tube and obstruct the passage of the gas4 ,again1 the gas-bag1 instead of being on the same level1 should be laid on a table1 so that any water accidentally driven from the purifier may not be forced into it4 ,the rubber tubes should have an orifice of nearly half an inch1 and should on no account contain an inside coil of wire4 ,previous to making gas the bag should be warmed for an hour or so in front of a fire1 so as to make it soft and pliable4 ,the cock should then be opened1 and the bag rolled tightly up so as to expel any air4 ,the tap should then be closed4 ,illustration3 ,,fig4 #b4 ,diagram showing relative positions of g b1 ,gas-bag2 w b1 ,wash-bottle2 and r1 ,retort4 ,when all is ready1 and every junction made except that between the bag and the pipe leading from the purifier1 the gas-stove may be kindled1 but turned down almost to its lowest point4 ,if this precaution be not observed1 the oxygen will come off with such rapidity as to be quite out of control1 and will probably blow the connections away4 ,in two or three minutes the gas will commence to bubble through the purifier1 at first intermittently1 but the bubbling will gradually become more regular1 until it is evident that oxygen is coming over in earnest4 ,the brightening of a spark at the end of a blown-out match1 held to the end of the purifier-tube1 will announce the fact that all the air has been driven out of the pipes1 and that gas has taken its place4 ,now is the time to connect the gas-bag with the purifier4 ,with a quick movement the indiarubber tube should be slipped over the nozzle of the bag with one hand1 while the tap is turned on with the other4 ,the gas should now come over regularly until the bag is nearly half full1 and this will occupy about fifteen minutes4 ,the action will then probably flag a little1 when the flame feeding the stove may be increased4 ,when the bag is nearly full the flame can be raised1 if occasion should require1 to its utmost4 ,some care is requisite in finishing the operation4 ,when the bag is quite full and as tight as a drum1 it should be disconnected before anything else is done4 ,of course at the moment of taking the tube from it1 the tap must be turned4 ,the next thing is to detach the retort from the purifier before the gas is extinguished in the stove4 ,this is a most important point1 for if the retort were cooled by putting out the gas first1 the water might be sucked into the retort from the purifier1 and a small steam-boiler explosion would be the result4 ,in an hour or so the retort will be cool enough to handle1 when the nozzle can be unscrewed and the vessel washed out with several changes of hot water4 ,it can then be dried and put away for the next occasion4 ,the retort-nozzle and its indiarubber tube should also be washed out1 or it may get clogged4 ,particular care must be taken to purchase the chlorate and manganese of some reliable dealer4 ,accidents have been reported owing to lamp-black1 bone-black1 etc41 having been supplied in error for the manganese1 which is a black powder much resembling them4 ,i find that the best plan is to buy several pounds of each at a time1 and to test a small quantity of the mixed ingredients in a test-tube over a spirit-flame4 ,if the gas comes off with a slight sparkling of the ingredients all is right2 but if there is anything approaching to an explosion1 the manganese is at fault4 ,one accident which ,i heard of was due to connecting the retort to the wrong side of the purifier2 the gas had no outlet1 and the retort exploded1 breaking all the windows of the room in which it was4 ,retorts are made either of copper or iron4 ,i have tried both1 and much prefer the latter1 which have also the advantage of being cheaper than the copper ones4 ,a good retort should serve for at least fifty charges1 and even then a new bottom can be put into it1 and it will do duty for another fifty4 ,but no retort will last long unless properly treated4 ,i am quite satisfied that the spent charge if allowed to remain has the effect of eating into the metal2 it should1 therefore1 be washed out soon after use4 ,the thickness of a retort after much use can be gauged by tapping it with the back of a knife when empty4 ,the oxygen gas is most usually stored in an indiarubber bag4 ,these vary very much in quality1 and the cheapest kinds are to be avoided4 ,the rubber should be soft and pliant1 and should be covered outside with stout twill4 ,a good bag will almost last a lifetime if it be only used occasionally4 ,i have had one for many years1 which looks shabby enough with constant use1 but seems to be as gas-tight and as efficient generally as the first day ,i had it4 ,even then it had been in use for some months by a friend4 ,illustration3 ,,fig4 #c4 ,iron bottle for compressed oxygen gas4 ,a bag full of gas is not the most portable thing that could be named1 and various attempts have been made to replace it by some contrivance of a more convenient character4 ,there is1 too1 the danger of accidental injury1 which can readily occur if the bag is carelessly handled4 ,in very cold weather1 for example1 some bags get quite stiff and hard1 and have to be almost thawed before they can be used4 ,neglect of this precaution will lead to cracks1 which will eventually turn into holes4 ,metal gas-holders--miniature copies of the big reservoirs seen at gas-works--which serve as travelling-boxes for the rest of the apparatus--are recommended by some1 but are seldom used4 ,perhaps the most convenient arrangement--which1 however1 is only suitable for a single lantern--is to employ an iron bottle in which the oxygen is greatly compressed4 ,such a bottle charged with gas can be obtained from several dealers1 and ,i have had some little experience of their use4 ,a bottle measuring three feet in length1 and about seven inches in diameter1 will hold about eight feet of compressed gas--sufficient for an ordinary evening's work4 ,at the end of the bottle is an opening closed with a tap which can only be opened by a special form of key4 ,into this orifice is screwed a nozzle1 upon which an indiarubber tube can be readily fitted4 ,when a bottle of this kind is used1 the amount of oxygen which reaches the lime must be directly controlled by this tap1 and not by the tap attached to the jet1 which must remain fully opened4 ,the reason of this is that the gas issues with such force1 that1 unless controlled in the way ,i have stated1 it will blow off the tubing by its pressure4 ,i found it so difficult to regulate the supply1 that ,i had an independent screw-tap made to fit on to the bottle4 ,this screw-tap is of the same pattern as those used on steam engines to control the supply of steam to the cylinder1 and with it ,i can adjust the oxygen supply with the greatest nicety4 ,my chief objections to the bottle system--which presents many advantages in the matter of portability--are1 firstly1 that you cannot charge the bottle yourself--it must always go back to the dealer for that purpose--and you are therefore dependent for one of your first requisites upon others2 and secondly1 you do not know how much gas you are using1 for you cannot see it diminish as you can when you employ a bag4 ,for these and other reasons ,i still prefer bags to store my gas1 and shall continue to do so until some improvement comes about4 ,illustration3 ,,fig4 #d4 ,gas-bag and pressure-boards4 ,the gas-bag is wedge-shaped1 and the thin edge of the wedge has in its centre a gas-cock for the entrance and exit of the gas4 ,the object of the bag being in this form is1 that it can conveniently be placed between the pressure-boards4 ,these1 in their simplest form1 consist of two boards strongly put together--the size of the bag which is used--which are hinged together at one end4 ,at the centre of this end1 and between the hinges1 is cut an oval opening through which the gas-cock is thrust4 ,a shelf on the upper board serves as a support for the weights4 ,at least two weights are required--one being sufficient at first1 when the bag is full2 the other being added later on when the pressure becomes reduced4 ,the weighted gas-bag should always be placed as near the lantern as circumstances will allow--in order that it may be under the eye of the operator--and the tube from it which supplies the lantern should be guarded1 so that it is not accidentally stepped upon4 ,the lime-cylinders are sold in air-tight tin canisters holding one dozen each4 ,they are of two qualities--hard and soft4 ,for work where large pictures are required--necessitating the use of the mixed jet with both gases under heavy pressure--the hard limes must invariably be used4 ,but where only a small sheet has to be covered1 and one gas only is subjected to the unusual pressure1 the soft limes will afford perhaps a better light than the harder ones4 ,occasionally the lime1 be it hard or soft1 will split4 ,in such a case it ought to be immediately replaced by a fresh one1 otherwise the flame may possibly be diverted towards the condensing lenses1 and will fracture that nearest to the light4 ,it is advisable always to keep a spare lime within the lantern1 lying on the tray to which the jet is attached4 ,by this means it gets warmed1 and ready for use if required4 ,lime is most absorbent of moisture1 and will1 if kept where air can get to it1 swell to double its former size1 and finally crumble to powder4 ,for this reason the tin canister containing the cylinders should have stretched over it1 when once opened1 a broad indiarubber band which will cover the junction between lid and box4 ,if this precaution be neglected1 the limes will swell with a force sufficient to break the tin-containing vessel asunder4 ,a compressed lime cartridge1 to which water is applied by artificial means1 has lately been successfully introduced to supersede explosives hitherto used for mining purposes4 ,this will show the immense power of expansion of which the substance is capable4 ,,the ,,screen ,,or ,,sheet4 ,and now a word about the best form of screen or sheet for showing lantern pictures upon4 ,the best possible form of surface is a smooth whitewashed wall2 but as this is not commonly found among the appointments of a sitting-room1 where the lantern will be wanted1 we must find some substitute which will most nearly resemble it4 ,a sheet of cartoon paper1 which can be bought of any length1 and measuring more than four feet across1 will do well if only a small disc is desired4 ,the paper can be rolled up out of the way at a minute's notice4 ,if a larger screen is wanted1 it can be made of stout calico1 faced with white paper1 and can be made to roll up and down like a school map of large dimensions4 ,a map-mounter1 or even an upholsterer1 would soon rig up such an arrangement4 ,there is a very effective way of showing small pictures and diagrams with an oil-lantern1 which ,i have more than once adopted1 where a room has been long in proportion to its breadth4 ,this is to make a wooden frame just large enough to take the full width of a sheet of tracing-paper1 and to put this screen between the lantern and the spectators4 ,tracing-cloth should be avoided1 as it is so transparent that the light streaming from the lens makes a blotch in each picture when seen through it4 ,if the lantern is brought into regular use--in a schoolroom1 for instance--it might be thought worth while to have a canvas sheet whitewashed1 and hung in the same manner that a stage drop-scene is fixed4 ,in making such a screen1 the canvas should be tacked on a frame1 and should have a coating of thin glue1 which should be allowed to dry before two or more coats of whitewash are applied4 ,it will be understood that a really opaque screen1 such as this represents1 is the more effective1 because the light1 instead of being partly lost--as it must be in penetrating an ordinary calico sheet--is reflected and utilized4 ,but for public exhibitions on a large scale1 the calico sheet is the screen commonly in vogue1 for it is conveniently put up and taken down1 and can be rolled into a bundle for easy transport4 ,a sheet properly hung should be as flat as a board and perfectly free from wrinkles of any kind1 and this can be accomplished without much difficulty by adopting the following method1 which is applicable to screens from twelve feet square upwards4 ,illustration3 ,,fig4 #e4 ,showing method of hanging a sheet4 ,the sheet should have at its top edge a strong cord sewn into its hem1 which cord should terminate at each side with a loop4 ,on its sides and bottom edges1 the sheet should have brass curtain rings sewn on to it at intervals of two feet4 ,having chosen the position of the screen1 a couple of screw-eyes are screwed into the roof1 or cornice near the top of the hall1 at such a distance apart that the sheet can easily go between them4 ,through each of these screw-eyes is passed a thin1 strong line1 having at its end a clip like that commonly attached to a dog's chain4 ,this clip is to clutch the loop of rope on each side of the sheet4 ,the sheet can now be pulled up into position3 the free ends of the cord being fastened to screw-eyes in the floor4 ,it now merely remains to lace with string the curtain rings on the side of the sheet to the adjacent cord1 and the arrangement is complete4 ,the annexed diagram shows the upper corner of such a sheet1 with its attachments1 as just explained4 ,where the hall is of such a height that this plan is not available1 or where the stern custodians faint with horror at the thought of their walls or ceilings being pierced with a screw-hole1 the same method can be carried out by fastening the screw-eye to a timber upright on each side1 supported by light struts4 ,some persons prefer a sheet stretched on a frame1 and such a frame of a very portable character can be easily devised4 ,the frame itself is best made of lengths of pine1 about the size of broom-handles4 ,these can be joined together so as to make a frame of any reasonable dimensions1 by six-inch lengths of brass tubing4 ,the same tubing1 mitred into ,l-pieces1 will serve for the four corners4 ,the sheet is furnished with tapes to secure it to the frame1 and the woodwork is kept in an upright position by strong cords fastened by screw-eyes to the floor4 ,the appearance of such a screen is much enhanced if the plain woodwork be hidden by a little drapery in the shape of narrow curtains at each side1 and festoons of the same material above4 ,,pictures ,,for ,,the ,,lantern4 ,before the advent of the art of photography1 pictures or slides for the lantern were traced on glass and painted by hand2 and this art was carried to very great perfection4 ,but no handiwork can equal the productions of the photographic camera2 so that when it was found possible to produce transparent positives on glass1 that could be magnified on the sheet to any extent without deterioration1 the occupation of the artist on glass was almost gone4 ,photographs are now almost exclusively used1 and form1 when properly executed1 the finest pictures for lantern use4 ,the manner of their production is fully described in my little book #8,how to ,photograph2' but as there may be many would-be lanternists who do not care to dabble in photography1 ,i will here give a few plain directions by which lantern slides can be extemporised4 ,the standard size for lantern pictures is #c #c inches4 ,the glass chosen should be as thin as possible1 and quite free from scratches1 bubbles1 or flaws of any kind whatever4 ,remember that a piece of the finest hair which may well be overlooked upon the slide itself1 will appear on the screen as a huge snake4 ,in like manner a tiny bubble in the glass is magnified into a blemish the size of a soup-plate4 ,glass presents a very difficult surface to draw or paint upon1 particularly if water-colours are employed1 but by coating it with a transparent medium in the first instance the difficulty is much reduced4 ,a film of plain collodion will1 when dry1 give a surface that can be easily sketched upon with a fine pen and ,indian ink4 ,the sketch so made can afterwards be filled in with water-colour1 tempered with prepared ox-gall1 and taking care that the colours used are those which are naturally transparent4 ,prussian blue1 indigo1 lake1 the madders1 gamboge1 burnt and raw ,sienna1 ,vandyke brown1 are all transparent pigments1 and will answer every purpose4 ,mixed with one another in the manner detailed in any manual of water-colour painting1 greens1 purples1 and all secondary and tertiary tints are readily obtainable4 ,another method1 and an easier one1 for producing lantern slides was introduced some years ago by the ,rev4 ,w4 ,h4 ,dallinger2 and although the author of the method intended it for drawings of microscopic subjects only1 and with that idea brought it before the notice of the ,royal ,microscopical ,society1 it will be readily seen that it is adapted to all manner of lantern pictures4 ,this method is best described in its inventor's own words3 #8,on finely ground glass drawing with a black-lead pencil is as easy as drawing upon cardboard4 ,i get squares of glass to suit the size of my lantern carefully ground on one side like the focusing-glass of a camera4' ,the author goes on to describe how1 by sketching upon the finely ground surface with a well-pointed hard pencil--,,hh or ,,hhh--and shading with a softer one1 such as ,,hb1 capital effects can be obtained4 #8,if it be necessary to put in colour it may be done1 cleanly and carefully over the shading2 thus one layer of colour suffices4 ,now1 of course1 although we have a perfect drawing of the object1 with all the detail accurately given1 it is not a transparency4 ,but we can easily make it one4 ,thin some good pale ,canada balsam with benzine to about the consistency of cream1 and simply float it over the ground surface of your glass2 pour off until the drop comes very sluggishly4 ,then reverse the glass so that the corner from which the balsam was flowing off be placed upwards4 ,let the return flow reach about the middle2 then reverse it again1 and move it in several directions to get the balsam level4 ,this may be done with a very little practice1 so that the surface shall be undistinguishable from glass4 ,we have now a perfect transparency4 ,all that is required is twenty-four hours for hardening 7keeping the glass level71 and then another square of glass fastened on to it by strips of paper at the edges1 with small pieces of card at the corners to prevent contact1 and it makes an admirable lantern transparency4' ,a hint about giving a fine grain to glass will not be out of place4 ,upon a perfectly flat and firm table lay a piece of glass say six and a half inches square1 for this size can afterwards be cut across into four lantern pictures4 ,a sheet of wet blotting-paper under the glass will keep it steady4 ,now pour upon its surface a mixture of flour-emery and water4 ,place another piece of glass above1 and work it round with a circular motion1 constantly spooning up the mud formed by the emery and water1 and which oozes out between the glasses1 and replacing it between them4 ,in a short time both glasses will be beautifully ground on the surfaces which have been rubbed together4 ,a moment's consideration will show that the ground effect is produced by the surface being broken up into innumerable tiny pits1 each one of which scatters the light4 ,by ,mr4 ,dallinger's method of filling up these pits with a glassy medium like ,canada balsam1 the glass is once more presented with a flat surface1 and therefore becomes once more transparent4 ,by whatever means the picture is produced the operator should have a glass transparent easel to work upon placed at an angle of forty-five degrees1 with a sheet of paper underneath it to throw the light up through the glass he is drawing upon4 ,a good easel can be made of a small frame--that belonging to a twopenny slate will do--attached to a base-board1 and supported on each side by struts4 ,a ledge of wood screwed across the frame makes a convenient support for the picture4 ,the annexed cut will sufficiently explain the arrangements described4 ,illustration3 ,,fig4 #f4 ,glass easel4 ,and now a word or two about mounting the picture4 ,as ,mr4 ,dallinger points out1 a cover-glass should be provided1 but it should be prevented from actually touching the painted surface4 ,this is best brought about by using the masks cut out of black paper1 and sold for the purpose4 ,a mask is inserted between the glasses1 after which the whole is fastened together by pasting a slip of paper round the edges of the double glass1 and turning it over on either side4 ,gum arabic with twenty-five per cent4 loaf-sugar added1 is a good medium by which to attach paper to glass4 ,illustration3 ,,fig4 #g4 ,masks for lantern slides4 ,,on ,,the ,,colouring ,,of ,,photographic ,,transparencies4 ,there are many amateur photographers nowadays who can produce fair transparencies for the lantern1 but at the same time there are many possessors of a lantern who know nothing about the #8black art4' ,luckily for these1 first-class pictures can be bought cheaply1 their average price ranging from eighteenpence to two shillings each4 ,any optician's catalogue will show what an immense variety of subjects there is to chose from2 not only can we obtain landscapes of nearly every part of the world1 but we can purchase figure studies1 copies of various pictures from books1 maps1 diagrams of scientific matters--micro-photographs and statuary4 ,these slides if coloured are double the price of plain ones1 and if very well coloured their price is quadrupled4 ,it would therefore be serviceable to many if they could learn how to colour such pictures for their own use1 and ,i give simple directions how this can be accomplished4 ,at the same time it is only fair to state that the work is really difficult1 and anyone to attain even slight proficiency in slide-painting must devote a great deal of time and patience to the subject4 ,the photographic slide as sold consists of two glasses1 one of which bears the photograph4 ,this is separated from the cover-glass by a paper mask1 the whole being bound round by a fillet of gummed paper4 ,after carefully cutting round this fillet the two glasses may be separated1 and the one bearing the picture is placed1 varnished side upwards1 upon the glass easel1 ready for colouring4 ,some colourists speak in favour of water-colours for glass-painting1 others prefer oil-colours1 while some1 ,i understand1 employ both on the same picture4 ,i have tried each system1 and most certainly recommend oil-colours as being both easier to work with1 and doing more satisfactory work into the bargain than water-colours4 ,the materials required comprise ordinary oil-colours in tubes1 of which the following are perhaps the most useful that can be employed for the purpose3 ,italian ,pink4 ,raw ,sienna4 ,yellow ,lake4 ,chinese ,orange4 ,brown ,pink4 ,prussian ,blue4 ,indigo4 ,neutral ,tint4 ,mc,gilp4 ,brown ,madder4 ,rose ,madder4 ,purple ,madder4 ,crimson ,lake4 ,burnt ,sienna4 ,ivory ,black4 ,it is curious to observe that the suitability of these colours for the particular purpose of glass-painting varies with the method of manufacture4 ,i find by experience that one maker's ,prussian blue is better than another's1 while for a suitable crimson lake ,i have to go to quite a different shop1 and so on4 ,the brushes used must be of the best1 the majority of them being camel-hair1 a few fine sables being kept for special touches4 ,it is also necessary to provide some good large bushy camel-hair brushes to be used as softeners4 ,a flat porcelain palette is better than one of any other material1 for the strength of the tints is seen well1 and the surface can easily be cleaned with a little turpentine4 ,a flexible palette knife must also be provided4 ,dabbers to soften down skies and other flat masses of colour can be made by wrapping a ball of cotton wool in fine wash-leather4 ,the leather should be first thoroughly washed with soap and water1 and it will be better if a little of the soap be left in it as it dries1 for this renders it soft and pliant4 ,both dabbers and brushes should be kept in a dust-tight box1 for dust is the greatest enemy of the slide-painter4 ,it will be noticed that the list of colours given includes those only which are transparent1 many others used in ordinary oil-painting being omitted4 ,it is obvious that opaque colours like ,naples yellow or chrome yellow would simply appear black on the sheet4 ,the tyro who is used to other methods of painting1 and has some idea of the harmony of colours1 will1 of course1 have an immense advantage over anyone without artistic knowledge or feeling2 and when he has once mastered the technicalities of the new work1 will soon be able to produce passable pictures4 ,the list of colours given is necessarily limited for the reason already given1 but their number can be increased indefinitely by judicious blending one with the other4 ,let me give a few instances4 ,there is no green in the list given1 simply because ,i do not know of a good transparent one4 ,but various tints of green suitable for foliage can be easily made up with the colours named4 ,prussian blue mixed with any of the yellows will at once give a crude green1 but it will not be suitable for use without the help of some other tint1 such as burnt ,sienna1 or one of the reds4 ,italian pink and indigo make a fine green4 ,italian pink1 brown madder1 and ,prussian blue is also another useful combination4 ,brown pink1 indigo1 and ,vandyke brown will be found admirable for the shadows in foliage2 indeed1 the combinations for this purpose are endless4 ,again1 there is a difficulty generally found in obtaining any approach to scarlet4 ,the best ,i know of is a mixture of ,italian pink1 crimson lake1 and ,chinese orange4 ,for browns1 ,vandyke brown1 ,chinese orange1 ivory black1 and burnt ,sienna1 will give any range of tints1 from the coldest to the warmest4 ,the reader will soon find by experiment the right proportions for mixing these colours to produce the desired effect1 and he will be much assisted in the work by studying any good manual of water-colour painting4 ,i recommend a water-colour manual in preference to one dealing with oil-colours1 because the first deals more with transparent tints1 which depend for their effect upon the white ground upon which they are laid4 ,in like manner a lantern picture depends much upon the white surface upon which the tints are subsequently exhibited4 ,our first attempt at glass-painting shall be an open landscape with figures in front--and we will suppose that the scene is laid in ,britain4 ,this would seem to some an unimportant point1 until they remember that the skies and atmospheric effects seen in some other lands would require an altogether different treatment4 ,i once coloured an ,egyptian scene for a friend1 and he admired my work1 with one exception4 #8,you have given me an ,english sky1' he said4 ,the sky will be the first thing to see to1 and we will endeavour to give it a flat tint of blue slightly darker at the zenith than it is at the horizon4 ,we squeeze out from its tube a little ,prussian blue upon the palette1 and dipping a good-sized camel-hair brush into a small cup of turpentine1 we take up a little of the colour and work it about on the palette until it seems of the right strength4 ,before applying it to the glass we add to it a very small quantity of ,mc,gilp medium4 ,having mixed this last addition with our brush-load of colour1 we can apply it to the glass1 painting it in broad bands from side to side until the sky is all striped with blue4 ,if the subject comprises a range of distant hills1 let them too partake of the blue tint4 ,when this is done1 lay aside the brush and let the coloured glass rest for a minute1 so that some of the turpentine will dry off4 ,now proceed to dab it carefully with one of the leather dabbers4 ,with a very light touch bring the dabber down over and over again1 and avoid anything like a rubbing action4 ,the movement must be vertical1 and not in the least horizontal4 ,by bearing a little more heavily on the dabber as the horizon is approached1 the tint will be sensibly lightened4 ,when this sky-colour has been uniformly dabbed in we may proceed to put in1 or rather wipe out1 some cloud effects4 ,a little piece of soft kid wrapped round a pointed pen-holder is a good tool to use for the purpose1 but a leather stump will answer the same end4 ,this part of the work requires a little judgment and artistic taste4 ,in a picture full of detail and which only has a small portion of sky exposed1 it is best coloured simply blue4 ,but where there is not much detail in the landscape1 as in the case for instance of a mill on a bleak moor1 the sky can be worked up with great advantage to the general effect4 ,the clouds are wiped out by a rubbing action combined with a dabbing movement1 so that the edges of the clouds formed remain quite soft4 ,if they appear too hard they can be corrected by a few gentle dabs with the top of the finger4 ,before the leather is laid aside1 it may be employed for wiping off any portions of colour which have accidentally been placed where they should not be4 ,but if there is water included in the subject1 such as a lake or river1 it will when the sky is reflected in it partake of the same colour1 and should be dabbed in at the same time4 ,we must now consider how we are going to treat the rest of our picture4 ,if there is some expanse of foreground it will make the best contrast with the sky if we use a warm sandy colour4 ,chinese orange1 raw ,sienna1 and brown pink mixed in various proportions to suit the lights and shadows of the picture will give the tint required4 ,at this stage1 too1 the middle tints of the composition lying between the sky and the foreground can also be laid in4 ,these will mostly consist of subdued greys1 made up of ,prussian blue1 burnt ,sienna1 purple madder1 and crimson lake4 ,when these tints are all dabbed in1 and the whole picture has been carefully gone over with the leather point1 so as to remove truant colour1 the slide may be laid aside to dry4 ,i find it a good plan to have a tin box containing grooves for this purpose4 ,the slides when grounded in in the way just described are placed in the grooves1 and the open box is turned towards a fire4 ,in an hour or so the colours are dry enough for further treatment4 ,we can now once more view our work on the easel1 and most probably we shall see much to amend4 ,the trees in the middle distance are too yellow1 or too blue4 ,they are easily corrected by a touch of the tint in which they fail4 ,but at this stage of the painting we must use a different medium for our colours4 ,we have done with dabbing1 and must now lay the colours on as smoothly as possible with the brush alone4 ,canada balsam in turpentine1 of the consistence of very thin varnish1 is perhaps the best medium to use4 ,it should be mixed with every colour as it is taken upon the brush4 ,the beginner will find some difficulty at first1 particularly if oil-colours are new to him1 in keeping his brushes in order4 ,he need not have a brush for every tint4 ,let one be kept for skies1 but only two or three others are necessary4 ,when ,i commence to paint a batch of pictures ,i put on my table1 after carefully dusting it all over with a damp cloth1 a sheet of newspaper4 ,in the centre stands my easel4 ,on the left hand my colour-box1 and on the right my palette4 ,close to the palette is placed a double thickness of clean white tissue paper1 and a small pot of turpentine4 ,when ,i wish to clean my brush1 it is simply dipped in turpentine1 and drawn over the surface of the white paper until ,i see that it leaves no trail of colour4 ,by this simple means one brush can be used for any number of tints1 for the cleansing of it does not occupy more than ten seconds4 ,it is in the foreground of a picture that the artist must be lavish with his bright colours4 ,if the figures in the subject will allow of bright colouring1 so much the better2 but it must be remembered that if these colours are not put in with some regard to contrast1 their effect is much diminished1 if not altogether lost4 ,let the painter remember that the principal colours have their complementary colours1 and that wherever we can place one of these tints against its complementary1 we are bound to have harmony4 ,thus the complementary of blue is orange2 of red1 green2 and of yellow1 purple4 ,but for further particulars of this nature1 the aforesaid #8,manual of ,water-,colours' must be studied4 ,when the picture is apparently finished1 it will1 most likely1 require some finishing-touches4 ,and here a new tool comes into use1 namely1 the etching-needle4 ,take a pointed piece of wood1 about the size of a penholder1 and bind upon it1 by means of waxed thread1 a good strong sewing-needle1 leaving not more than a quarter of an inch of the point exposed4 ,a few judicious touches with this needle will make a vast difference in the effect of a picture1 but anything like coarse scratching must be avoided4 ,the beginner will do well to view his work in the lantern as it gradually progresses1 for what may look very well on the easel1 will look very different when all its imperfections are magnified on the screen4 ,the art of slide-painting is one which requires constant care and practice before anything like proficiency is attained4 ,in case some of my readers should be well acquainted with the use of water-colours1 and may be deterred from trying the art of glass-painting because oils only are recommended for the work1 ,i will briefly describe how water-colours are utilized for slide-painting4 ,at the same time1 ,i hold to my previously expressed opinion1 that oil-colours are the more suitable pigments to use4 ,the varnished surface of a glass picture does not take kindly to water-colour1 and as the brush is applied to it there is a repellent action which would make the painter despair if some means were not at hand to obviate the difficulty4 ,by mixing each colour with a certain proportion of prepared ox-gall the difficulty vanishes1 and it is a wise precaution to rub a little ox-gall and water over the surface of the picture by means of a tuft of cotton wool1 before any colour is applied at all4 ,the same transparent colours as those recommended for oil-painting may be employed1 besides a few more transparent tints which are commonly not ground up in oil4 ,but the dabbers are of a different description4 ,procure two or three good thick camel-hair brushes1 and cut the hair off straight with a pair of scissors1 so as to leave the ends of the hairs like a flat stump4 ,now carefully turn the brush round and round in the flame of a spirit lamp1 or candle1 so as to just singe the point of each hair4 ,when this is done1 rub the ends of the hair on the finest glass-paper until every trace of singeing has disappeared4 ,this treatment will leave the brush with a flat woolly head like a mop1 which makes an excellent dabber4 ,when the sky-colour has been applied as evenly as possible1 and has been allowed to dry1 the surface may be worked over with the dabber4 ,but1 before doing this1 gently breathe over the colour4 ,the dabber will remove little particles of the pigment1 and will reduce the general strength of the tint1 so that this loss should be provided for when the colour is first applied4 ,clouds1 etc41 can be wiped out with the leather1 after the breathing operation1 and in many other respects the two modes of colouring agree4 ,when the general tints have been laid in1 the colours may receive a coat of mastic varnish1 and this again can be worked over with colour to strengthen those tints which may require it4 ,the varnish also confers a transparency upon the tints that they do not possess without it4 ,,showing ,,solid ,,opaque ,,objects ,,on ,,the ,,lantern ,,screen4 ,those who are familiar with the working of the microscope know that the objects which are employed in that instrument can be viewed in two different ways4 ,transparent preparations have the light thrown through them by means of the adjustable mirror beneath the stage4 ,opaque objects1 on the other hand1 must have light thrown upon them from above1 and this is managed by means of a separate condensing lens4 ,for the magic lantern1 transparent pictures are almost wholly employed2 but there is a means of utilizing paper prints1 photographic cartes de visite1 and a certain limited number of solid objects1 so that they may be shown in an enlarged form on the sheet4 ,the effect is not so bright as when transparencies are employed1 for a large proportion of the available light is absorbed in the operation2 but there are many who would sacrifice a good deal in the way of effect1 for the undoubted advantage of being able to utilize the contents of their albums1 etc4 ,illustration3 ,,fig4 #h4 ,ground-plan of ,chadburn's ,opaque ,lantern4 p1 ,picture2 c1 ,condenser2 l1 ,light2 r1 ,reflector2 o1 ,objective4 ,the first instrument which was constructed to accomplish this end is known as ,chadburn's lantern2 and1 as will be seen from the annexed diagram1 it differs very much from the ordinary form of magic lantern4 ,from what has been already said concerning the loss of light1 it will be evident that a powerful luminant is a matter of prime consideration4 ,a good oil-lantern will do the work--but not so well as the lime-jet4 ,the luminous face of the lime1 instead of being turned towards the optical system1 is opposite a concave reflector placed at the back of the lantern4 ,from this the light is reflected towards the condenser1 which condenser concentrates the light obliquely upon the object4 ,the picture or object is contained in a kind of box joined to the main lantern1 and which holds immediately opposite the illuminated picture the lens for projecting its image upon the screen4 ,this pioneer form of opaque lantern has been superseded by the instrument called the ,aphengescope4 ,this can be purchased now of most opticians4 ,virtually it consists of the front chamber of ,chadburn's lantern constructed to fit on to the front of any ordinary oil or lime-lit lantern4 ,the aphengescope can be used for showing woodcuts1 paper photographs1 printed and written matter of any kind1 so long as the space covered is within the size of the instrument4 ,thus any caricatures from our comic publications could be pasted on card1 and enlarged by its means4 ,but it will be readily observed that this class of subjects1 if photographed as transparent positives and used in the ordinary lantern1 can be shown far better4 ,the principal use of the aphengescope is to show solid objects which cannot by any possibility be shown enlarged without its help4 ,let us suppose1 for instance1 that it is desired by some collector to show his friends a cabinet of coins and medals4 ,such objects are so bright in themselves that they are admirably adapted to this instrument4 ,their form1 colour1 and minute markings are faithfully reproduced2 whilst the raised portions catch the reflected light in such a way as to make the images look as solid as the objects themselves4 ,at the ,polytechnic ,institution1 a lecture upon the invention of the watch1 and its gradual development1 was beautifully illustrated by the opaque lantern4 ,first came the different parts of the watch1 and then the varied movements4 ,it was most curious and instructive to see the wheels and springs all in movement upon the screen4 ,there are also many natural things which can be shown by the same means4 ,a freshly opened oyster makes a very remarkable object4 ,a still more curious effect is obtained by concentrating the light upon a freshly cut orange or lemon4 ,when the fruit is squeezed1 the pips and juice appear to fly upwards2 for1 of course1 everything is shown upside down1 as in the ordinary lantern4 ,the opaque lantern was once introduced into a court of law in ,america1 as a witness for the prosecution in a case of forgery4 ,the following is a condensed account of the occurrence1 taken from a ,new ,york paper3 #8,during the recent trial1 it became necessary to show the differences between a genuine signature and an imitation or forgery of the same4 ,for this purpose1 there was brought into court a powerful reflecting magic lantern4 ,the room was darkened1 and images of the two signatures1 enormously magnified1 were thrown side by side upon a screen before the judge and jury4 ,the false signature was at once revealed4 ,the illumination of the writing was effected by means of two powerful lime-lights contained within the lantern4 ,the peculiar arrangement of the lights and screen enables the examiner to discover the surface of the paper through the ink1 so that patching1 shading1 or painting of letters becomes evident the instant it is brought under the focus of the lantern4 ,an arrangement of screens1 by which the light is cut off alternately from either side of the instrument1 discovers any tampering with the surface of the paper1 either by scratching or washing by chemicals4 7,in other words1 by throwing the light alternately from either side1 the relief caused by the grain of the paper is clearly shown2 and any tampering with that relief1 by scratching or otherwise1 at once becomes apparent47 ,the instrument1 in this case1 was of sufficient capacity to view at once two bank-notes placed side by side1 and the pictures were of such fineness that there was no difficulty in viewing their smallest details4 ,i fear that the introduction of a magic lantern into an ,english court of law would be rather too sensational for the ordinary legal mind--particularly as the evidence of an expert1 with the help of a microscope1 would answer the same end4 ,under the name of the ,physioscope1 an immense opaque lantern was exhibited some years back in ,london4 ,the object magnified on the sheet was the human face1 and a correcting lens was included in the apparatus1 so that the face was seen right way up4 ,it was always rather an unhappy face1 for the individual who lent his countenance to the transaction had on either side of him1 and within a few inches of his cheeks1 a very powerful lime-light1 the heat and glare from which were sufficient to render anyone uncomfortable who was not a salamander4 ,,the ,,lantern ,,microscope4 ,of late years it has become possible to take very beautiful photographs of microscopic objects1 which1 when used as lantern-slides1 give a very fine effect4 ,numerous slides of this character may now be purchased1 which cover a vast field of microscopic knowledge1 and many will be content with what they can thus obtain4 ,but there is another class of workers who1 perhaps possessing a large number of microscopic slides1 will be glad to utilize them for the lantern1 so that they are no longer limited to the individual eye4 ,for these the lantern microscope1 which will screw in front of the lantern in place of the usual optical system1 is a most useful instrument4 ,different makers advertise in their catalogues lantern microscopes which range in price from twenty-five shillings to as many guineas4 ,and it recently came to my knowledge that a well-known ,london optician has undertaken the construction of a few of these instruments at the price of #aej each4 ,the amateur lanternist will1 therefore1 have some difficulty in deciding what he ought to pay for such an instrument4 ,and it is most difficult to advise him on that point4 ,his best plan is1 perhaps1 to see for himself what the makers can offer him1 and1 if possible1 to seek a trial of the instrument before he purchases it4 ,the lantern microscope is a modification of the old solar microscope--an instrument which could be screwed against a hole in the shutter of a darkened room--and which had a mirror outside which projected a beam of sunlight through it4 ,the objective lenses were uncorrected1 and small in aperture1 so that the instrument was far from being a perfect one4 ,but the intensity of the solar light covered many objectionable features1 and it was possible to get some astonishing effects with the contrivance4 ,but sunlight is such an uncertain commodity in our climate that1 when the lime-light came into prominence1 the old solar microscope was forgotten in favour of that which depended upon a more constant1 if a far less intense1 light source4 ,the great difficulty to overcome in the lantern microscope is to get the light sufficiently intense to well illuminate the objects4 ,the aperture of a microscope objective1 even of low power1 is so small1 that1 when the pencil of light which it emits is spread over a screen1 the light is so attenuated that the details of the object are difficult to make out4 ,in the near future1 when we are promised that electricity shall be laid on to our homes1 as gas is now supplied to us1 the difficulty will disappear1 for the electric-arc light is many times more intense than the most powerful lime-jet4 ,having obtained a lantern microscope1 the next thing to consider is the class of objects which can best be shown with it4 ,to help the reader in determining this point1 ,i will now give a kind of sketch of a popular lecture to accompany an exhibition of the instrument4 ,such a lecture might usefully commence with a brief description of the microscope3 its history1 and how1 in its improved form1 it has opened up a world of minute life1 of which our forefathers could have had no conception4 ,we might then put forward a few remarks as to the adaptation of the microscope to the oxyhydrogen lantern1 and point out how by its aid a number of persons can at the same time see what1 in an ordinary microscope1 is visible to only one person4 ,so much by way of introduction4 ,we might next enlarge upon the circumstance that the contents of the world have been classified into three general divisions--popularly known as the three kingdoms of ,nature3 the ,mineral ,kingdom1 the ,vegetable ,kingdom1 and the ,animal ,kingdom4 ,show how one is dependent upon the other1 and the difficulty in many cases of drawing a line to separate the minute organisms of the ,animal ,kingdom from those of the ,vegetable ,world4 ,numerous examples from the lower forms of life may be quoted to illustrate this4 ,now show and explain subjects from each of the three divisions1 taking the minerals first4 ,define a mineral1 and show how they crystallize in definite forms4 ,illustrate the process of crystallization by putting a drop of a saturated solution of sal-ammoniac on a slip of glass1 and spreading it over with a brush4 ,such a glass placed in the microscope will1 as it dries1 become covered with branches of crystals1 which seem to grow and strike out in various directions on the sheet in a truly marvellous manner4 ,sections of various minerals may next be shown1 finishing with sections of coal4 ,in pointing out the origin of coal from plants1 we may easily drift into the next division of our subject--the ,vegetable ,kingdom4 ,here we have indeed a wide field to illustrate4 ,commencing from the simple cell1 as exhibited1 for instance1 in a bit of so-called green mould1 and arriving gradually at sections of different stems of plants 7which by the way form most beautiful objects on the screen71 sections of different woods1 parts of flowers1 etc4 ,from these it will be easy to step over the indistinct boundary-line which separates us from the ,animal ,world4 ,here we can commence with the lowest organisms2 next show the living inhabitants of our ponds and ditches4 ,arrive at the ,insect ,world1 and show the generally unfamiliar parts of familiar insects--bees1 wasps1 flies1 etc4 ,we can then go higher1 and exhibit sections of bone1 hair1 etc42 finishing with the structure of the human body1 so far as it can be indicated by means of the microscope4 ,this is a brief sketch of the kind of entertainment the microscope is able to afford1 which can be modified to suit the views of the exhibitor4 ,,mechanical ,,or ,,moving-,,pictures4 ,the most common form of moveable slide is that known as a #8comic slip4' ,this mechanical contrivance for the amusement of youth is generally of the coarsest execution1 and it speaks little for the originality of our slide-producers that the same old things should appear in catalogues year after year with no improvement4 ,the #8comic slip' consists of a glass in a wooden frame1 with another loose piece of glass which can work backwards and forwards in front of it4 ,this movable glass generally serves as a mere screen to cover something painted underneath it1 and it is rubbed over with black varnish so as to be opaque4 ,thus a gentleman is represented with a nose of the normal size1 but as the screen is withdrawn it elongates to an awful extent4 ,or a woman's tongue may be graphically1 if not elegantly1 portrayed in the same manner4 ,in another class of slide a circular glass is kept in slow rotation in front of the slide proper by means of a rack-work attachment4 ,a common design for this device is a landscape with a windmill in the centre4 ,the sails of the mill are painted on the revolving glass1 and can be kept in rotation as long as desired4 ,the chromatrope effect is managed in the same way1 only that in this case both glasses are caused to slowly revolve in reverse directions4 ,there are many people who admire chromatropes1 and many others who regard them as rather trying to the eyes4 ,rippling water1 the rising or setting of the sun or moon1 and astronomical slides illustrative of the movements of the heavenly bodies1 are among the subjects which can be well illustrated by mechanical means4 ,perhaps the cleverest piece of apparatus ever invented to give the effect of movement by means of a magic lantern is ,beale's choreutoscope4 ,this instrument depends upon the well-known phenomenon common to our eyes1 called persistence of vision4 ,the image of anything that we look at is cast upon the retina at the back of the eye by the agency of the crystalline lens1 which is placed behind the pupil4 ,so far1 the human eye resembles a camera obscura4 ,persistence of vision means that an image so cast upon the retina remains impressed there for about the eighth part of a second4 ,for this reason we wink continually without knowing it1 for the light impression remains with us during the short time that the eye is closed in accomplishing that necessary action4 ,a burnt stick with a red-hot end whirled round and round appears to us like an unbroken circle of fire4 ,the separate drops of rain as they fall from the sky look like streaks of water1 and so an artist will represent them in his picture4 ,a quickly moving meteor looks like a long trail of fire for the same reason4 ,in the choreutoscope we have a very elegant adaptation of the same principle4 ,it consists1 in its commercial form1 of a slide arrangement that can be placed in any lantern4 ,this contains a narrow strip of glass1 with1 say1 six figures painted upon it1 each figure having a different position4 ,a dancing man is a good representative of the rest4 ,by a turn of a handle each figure is brought into view successively1 but so rapidly as to give the effect of moving arms and legs4 ,an interceptor or screen runs in front of each figure as the change occurs4 ,one of the best designs made for this instrument is a dancing skeleton 7see annexed cut74 ,in this case the figures are cut stencil-fashion out of very thin brass1 and the openings thus cut transmit so much light that the effect is far more brilliant than if the design were executed on glass in the usual manner4 ,the choreutoscope is not only a most amusing contrivance1 but it illustrates in a very beautiful manner this optical law called #8persistence of vision4' ,illustration3 ,,fig4 #i4 ,facsimile of a dancing skeleton for ,beale's ,choreutoscope4 ,,concluding ,,remarks4 ,the best lantern and the best pictures will not interest an audience unless the entertainer or lecturer is up to his work1 and the matter which he conveys is skilfully put together4 ,i believe that lecturing would be far more popular among us had it not been for the numbers of utterly incompetent men who have in past years bored audiences to such an extent that the word #8lecture' is to them as a red rag is to a bull4 ,when ,i say incompetent men1 ,i do not mean uneducated ones2 but ,i mean those who from natural want of voice1 and utter ignorance of its management1 are generally unfit for public speaking4 ,it seems to be too often conceded that because a man has written a book--or done something else which has brought him before public notice--he is1 without any previous knowledge or practice1 fit to lecture on the particular subject with which his name is identified4 ,or his claims to recognition as a lecturer are based upon certain cabalistic letters after his name1 which in many cases represent only so many guineas yearly subscribed to those who confer them4 ,lecturing is an art that can only be acquired successfully by those who have certain qualifications for the work1 and among these the foremost is the power of imparting knowledge to others in a common-sense and interesting manner4 ,luckily for him1 the amateur lecturer is likely to meet with a far more indulgent audience than those which professional men have occasionally to face2 but this is no reason why he should be careless as to his method of delivery1 or of the matter delivered4 ,perhaps the er--worst fault er--which a lecturer can er--fall into--is the one indicated er--in this sentence4 #8,to err is human1' in a wider sense1 unfortunately1 than ,pope1 the writer of that well-known line1 ever dreamt of4 ,unless a would-be lecturer can conquer this tiresome habit1 or any other trick of speech which he may have cultivated1 by all means let him confine himself to the management of the lantern while some one else acts as showman4 ,if two people are thus managing an exhibition between them1 and if the room be large1 so that they are widely separated1 some signal from the lecturer to indicate that he wants the next picture thrown on the screen becomes necessary4 ,a bell1 or anything that makes a noise1 is distracting both to lecturer and audience4 ,still worse are verbal instructions from one to the other4 ,i myself use an electric single-stroke bell with the gong removed1 the hammer of which gives a little click unmistakable to the operator1 but quite unheard by the audience4 ,such a bell can be placed close to the lantern1 while its push is far away on the lecturer's desk4 ,sometimes a string can be carried from lecturer to operator1 a gentle pull of which will give the necessary signal4 ,some lecturers signal by uncovering a little pane of red glass in the back of their reading-lamp4 ,but ,i think that any sight signal is inadmissible1 because the operator has quite enough to do in attending to his duties without having his attention thus distracted4 ,the signal1 of whatever nature it be1 should be given by the lecturer some seconds before he has finished with the picture in hand1 otherwise there is an awkward pause while the operator makes the necessary change4 ,before the lecture begins1 the reader should make himself not only thoroughly familiar with his subject1 but should be also familiar with the different pictures which illustrate it4 ,and this especially applies to the common case of those who have purchased or hired a set of slides and a published lantern reading--many of which are compiled by writers of repute1 and are in every way excellent4 ,let him1 then1 carefully go through the reading beforehand1 comparing each picture with the text1 and making himself so familiar with its details that he is afterwards able1 during performance1 to point out anything to which attention may advantageously be directed4 ,particularly is this necessary in the case of an introductory map1 where places of importance to the subject in hand must be pointed out4 ,the most convenient form of pointer1 by the way1 is a ,japanese fishing-rod1 which telescopes into small compass when not in use4 ,for an evening's lantern entertainment to be successful1 a great deal depends upon the operator4 ,with a mineral-oil lamp in a small room1 his duties are not very onerous1 for the lamp when once established should require no further attention1 except it be to turn down a wick which shows symptoms of smoking4 ,but he should be careful to have in reserve a glass or two to replace the front glass of the combustion-chamber1 which may crack through some unexpected draught of air4 ,his slides must all be numbered and in order4 ,they may be each mounted in a wooden frame to fit the lantern stage1 or else the lantern may be fitted with a permanent grooved slide in which the glass pictures are placed one after another1 the last one pushing out the one before4 ,another plan1 which is a good one to adopt where a single lantern only is being used1 is to make use of what is called a panoramic slide4 ,it is constructed like the one just described1 only it is furnished with a travelling tape upon which each picture rests4 ,the turn of a handle moves the tape1 and the pictures travel forward panorama-fashion4 ,in the use of a double lantern furnished with lime-jets1 there is plenty for two hands to do1 for the operator has to keep his attention fixed not only upon the business of changing the pictures1 but upon the condition of the lights4 ,as the pressure of the oxygen gas varies as it is gradually consumed1 so the supply of the two gases to the jets will want constant adjustment if the maximum quantity of light is expected4 ,extra weights1 too1 must be added as the pressure-boards gradually sink down4 ,beyond carefulness in this respect1 the lantern operator must see to the occasional turning of his limes1 taking care to do this when the lime wanting attention is not in actual use4 ,he should also find time to wipe the glass of each picture with a leather before putting it in the lantern1 for a film of moisture condenses on the surface1 particularly in a room full of people4 ,the success of a lantern entertainment depends nearly as much on the competence of the assistant as it does on the powers of the lecturer4 ,i am perhaps fastidious on this point1 for my lecturing apprenticeship was served at the late ,royal ,polytechnic ,institution1 where operators were employed who had spent the best part of their lives in this particular work4 ,it was seldom1 indeed1 that they made a mistake4 ,,the ,,end4 ,,billing ,,and ,,sons1 ,,printers1 ,,guildford4 ,transcriber's ,notes3 ,italics are shown thus3 sloping4 ,variations in spelling and hyphenation are retained4 ,perceived typographical errors have been changed4