diff options
Diffstat (limited to '75890-0.txt')
| -rw-r--r-- | 75890-0.txt | 1669 |
1 files changed, 1669 insertions, 0 deletions
diff --git a/75890-0.txt b/75890-0.txt new file mode 100644 index 0000000..fc2e20f --- /dev/null +++ b/75890-0.txt @@ -0,0 +1,1669 @@ + +*** START OF THE PROJECT GUTENBERG EBOOK 75890 *** + + + + + + THE MAGIC LANTERN + + _AND ITS MANAGEMENT_. + + + + + THE MAGIC LANTERN + + _AND ITS MANAGEMENT_ + + INCLUDING + + _FULL PRACTICAL DIRECTIONS FOR PRODUCING THE LIME + LIGHT, MAKING OXYGEN GAS, AND PREPARING + LANTERN SLIDES_ + + BY + + T. C. HEPWORTH + + LATE LECTURER ON SCIENCE TO THE ROYAL POLYTECHNIC + INSTITUTION, LONDON. + + [Illustration] + + London + CHATTO AND WINDUS, PICCADILLY + 1885 + [_All rights reserved_] + + + + +PREFACE. + + +During the past few years, 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 capabilities, such as few scientific instruments can command. +The Magic Lantern is now closely allied with the camera, for there +is no means of showing the perfection of a photographic picture so +well as by its aid. 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 management. +It is for these that the following pages have been written, in which +I have tried to place clearly before the reader what can be done, +and how to do it. I have also tried to indicate the educational value +of the lantern, and have pointed out in a necessarily brief manner +how various branches of knowledge can be illustrated by its aid. The +numerous personal inquiries addressed to me after my lectures, and +the numbers of letters constantly received, asking for information +regarding the lantern, its management, and the preparation of lantern +slides, have convinced me that there is room for a manual, humble +though it be, dealing with these subjects. + + T. C. HEPWORTH. + + 32, CANTLOWES ROAD, + LONDON, N.W. + + + + +CONTENTS. + + + THE HISTORY OF THE MAGIC LANTERN. + + PAGE + + The introduction of mineral oil lanterns.--The advance + caused by the aid of photography.--The optical + system of a modern lantern.--Educational value of + the lantern 1-12 + + THE LIME-LIGHT. + + Different forms of lime-jets.--Precautions to be observed + in their use 12-16 + + DISSOLVING VIEWS. + + The old method and the new.--The biunial lantern.--The + dissolving-tap and its management.--Coincident + discs.--‘Effects’--The application of the + double lantern to spectrum analysis 17-22 + + MAKING OXYGEN GAS. + + Necessary precautions.--The purifier.--Explanatory + diagram.--Practical details.--The retort.--The + gas-bag.--Iron bottle for compressed gas.--Pressure-boards. + --Lime cylinders 22-33 + + THE SCREEN OR SHEET. + + Arrangement adapted to a sitting-room.--Public exhibitions. + --Method of hanging a large sheet.--Sheets + on frames 33-37 + + PICTURES FOR THE LANTERN. + + Photographic slides.--Home-made pictures.--Drawing + pictures on ground-glass.--The slide-painter’s + easel.--Mounting slides 37-43 + + ON THE COLOURING OF PHOTOGRAPHIC TRANSPARENCIES. + + The process described.--Oil-colours employed.--Apparatus + required.--Mixed tints.--How to lay on the + colour.--Finishing touches.--Painting in water-colours 43-55 + + SHOWING SOLID AND OPAQUE OBJECTS ON THE LANTERN + SCREEN. + + Chadburn’s opaque lantern.--The aphengescope.--Showing + coins, medals, etc.--The opaque lantern + in a law court.--The physioscope 56-61 + + THE LANTERN MICROSCOPE. + + Photographic microscopic slides.--The solar microscope.--A + sketch lecture 61-65 + + MECHANICAL OR MOVING PICTURES. + + Comic slips.’--Beale’s choreutoscope.--The dancing + skeleton 66-69 + + CONCLUDING REMARKS. + + The management of the lantern in public.--Signals + between lecturer and operator 70-75 + + + + +THE MAGIC LANTERN + +_AND ITS MANAGEMENT_. + + +There is no optical instrument so well known or so highly held in +popular estimation as the Magic Lantern. It is somewhat unfortunate +that its old appellation, given to it when it was nothing more than a +mere toy, should have stuck to it so long. And more than one attempt +has been made by those conversant with its capabilities as a scientific +instrument, and as an important aid to education, to give it a name +more consistent with its real value. The late Mr. Dalmeyer was, I +believe, the first to re-christen it the ‘Optical Lantern;’ and there +is evidence that others are adopting the term, and that in time the old +name will sink into oblivion. + +With regard to the early history of this deservedly favourite +contrivance, but little is known. Its invention has been ascribed to +Friar Bacon, but the evidence on this point is of the most legendary +character. It seems, however, certain that the first to give an +intelligent description of it was Kircher--a Jesuit who lived two and +a half centuries ago, and who published a work entitled ‘Ars Magna +Lucis et Umbræ,’ or ‘The Great Art of Light and Shadow.’ The body of +the lantern, as described by Kircher, consisted of a room several feet +across, furnished with an opening in which a lens was placed. The +source of light was an oil-lamp, and the pictures for exhibition were +of the roughest kind. Indeed, we may presume that the effects produced +fell far short of those attained by the cheapest toy lantern of our +schoolboy days. Even if we search the columns of an Encyclopædia or any +similar book of reference of forty years ago, we shall not find any +great improvement on the description afforded by Kircher. The magic +lantern will there be found described as ‘an optical toy, by which +glass pictures executed with coloured varnishes can be thrown upon a +wall or screen.’ + +But from this time a gradual improvement began. First, the old oil-lamp +was replaced by the argand burner; then came gas; finally the +brilliant lime-light--and some time in the near future, perhaps, will +come electricity. The improved means of obtaining light have naturally +led to larger pictures being thrown on the screen; for the size of +such pictures is governed only by the amount of light available. Thus, +supposing we own a modern lantern constructed with one of the improved +three or four-wick lamps, and that it will give us a good picture of +about six feet diameter, by using the same lantern, and without any +change whatever in its optical arrangements, save fitting it with a +lime-light jet, the disc can be increased to fifteen feet diameter. +A picture of the same size could be produced with the original lamp, +provided that the operator retired to the necessary distance from the +screen, but the light would be so attenuated that the picture would be +but a ghost of what it ought to be. 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 lens, and may be of any size; but to +render it practically available its size, and therefore its distance +from the lens, must be regulated by the amount of light at disposal. + +During the past few years two circumstances have combined to render the +optical lantern more popular than ever: one being the introduction of +photographic transparencies representing scenes from the remotest parts +of the earth, and the other the construction of metal-bodied lanterns +of improved character, and burning mineral oil. As a good paraffine +lamp is compared with a farthing rushlight, so is one of these lanterns +to the toy of our boyhood. The light given, although it falls far short +of the brilliance of the lime-light, is much more intense than could +have been hoped for some years ago from oil. But its brilliance is not +all due to the paraffine, but quite as much to the careful ventilation +and general construction of the flame-chamber. There is, too, no danger +in the use of this form of lantern, for the reservoir containing the +paraffine is far below the combustion-chamber, and therefore it cannot +become unduly heated. + +The lenses, too, in this new form of lantern, although placed in the +same position as those in the old-fashioned magic lantern, are of a +very different stamp. And this leads me to a brief consideration of the +optical system comprised in these instruments. + +[Illustration: FIG. 1. + +L, Light; _c_, _c_, Condensing lenses; _o_, _o_, Objective lenses.] + +There are two sets of lenses: one being known as the condenser, and +the other as the objective. The condenser is made up of two or more +glasses, the usual form consisting of two plano-convex lenses placed +face to face. The duty of this condenser is to take up as much as +possible of the light afforded by the lamp, and to change the direction +of the rays so that they are cast through the picture or slide placed +in front of it. A glance at Fig. 1. will show how this is accomplished, +and how the rays indicated by the dotted lines would be lost if not +turned to account by the condenser. The use of the objective, on the +other hand, is to magnify the image of the picture, and to present +it in as perfect a form as possible on the screen placed for its +reception. Its distance from the picture is governed by the distance +of the lantern from the screen, and can be regulated to a nicety +by the focusing screw attached to it. It is generally acknowledged +by all acquainted with the requirements of the lantern that the +photographic camera lens (known as the quarter-plate portrait lens) +fulfils admirably this duty; and this particular form of lens, which +is by no means expensive, is generally fitted to modern lanterns of +the mineral-oil type. The condensers vary from four to three inches +in diameter; perhaps the best size is three and a half inches. The +relative positions of condenser, light, slide, and objective are +indicated in the diagram to which attention has just been called, Fig. +1. + +The optical lantern always inverts the image of any picture projected +by it, an inconvenience readily obviated by placing the slide on the +stage upside down. At the same time the picture must have its front +turned towards the condenser, not away from it, otherwise every part +of the slide suffers reversal on the screen. In some cases this +does not matter, but when any wording, such as that on a signboard, +for instance, is contained in the picture, it reads backwards. +Such accidents can be prevented by a white label, easily seen in +semi-darkness, placed in a certain position on the picture. If such +a precaution had been observed at a certain exhibition at which I +was present, General Garfield would not have been shown standing on +his head--not a dignified position for the President of the American +Republic. + +The first lanterns, constructed to burn mineral oils, were very +different to those of modern make, and took their pattern from the +cumbrous instruments which before them were provided with colza-oil +lamps. The reservoir for the oil was carefully kept in a cistern at +the back of the lantern, and bubbled through a pipe to the lamp on +the same principle that water is supplied to an earthenware poultry +fountain. It was doubtless thought necessary in those days to maintain +the paraffine in the cistern at a height equal to or above the wick, +as in the case of colza and other heavy oils. 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 combustion. By the time that the liquid reaches this point, +it has become so heated in the course of its passage along the metal +wick-holders that it issues as a gas. This can be readily proved by +turning down the wicks after the lantern has been burning some time, +when the flames will remain above the wick-holders, although the wicks +themselves have been turned down quite out of reach. In the older +lanterns, too, the glass chimney was thought to be indispensable, but +now this has been done away with, and with it the cylindrical wick has +also gone. The modern combustion-chamber is made of charcoal iron, and +is closed at one end with a thin pane of glass, just outside which the +condensing lenses are placed, and at the other end by a silver-plated +reflector. The necessary air to promote combustion is admitted by +suitable orifices below, and a draught is established by a long iron +chimney above. + +There is no great difficulty in managing one of these lanterns. The +loosely plaited cotton wicks should in the first instance be carefully +cut parallel with the wick-holders. After this they do not require +much attention. It is a far better plan to remove the charred end of +the wicks by scraping them along with the back of a knife, than to be +always cutting them afresh. However, any loose strands that may project +from the cotton should be certainly snipped off with scissors. + +After lighting the lantern--which is best done with a long +wax taper--each wick should be turned down quite low, and the +combustion-chamber closed. In about two minutes, by which time the +front glass and the lantern generally will have become warmed, the +wicks should be turned up to their highest; that is to say, to a pitch +just short of smoking-point. If the wicks are turned low for any length +of time the lamp will be sure to smell. It will also smell if, in the +process of charging with oil, some of the liquid has been smeared +against any part of the lantern which may afterwards become heated. The +best oil only should be used. + +I have already hinted at the educational value of the optical lantern, +but those who have not experimented with it have but a faint idea of +its capabilities in this respect. I am of the opinion that every school +and college should possess one, and that both pupils and teachers would +soon discover its many advantages. Now that it is manufactured in such +a portable and efficient form, and can be so easily managed, there +is no possible hindrance to its adoption, unless it be its old name +of ‘magic lantern,’ which is associated with things too childish for +consideration. But this objection cannot hold good when it is pointed +out how many different branches of knowledge can be illustrated by its +use. + +The schoolmaster of a London Board School once told me of some of +his difficulties in teaching such a subject as geography. Most of +the children had never seen the sea, and many of them had never even +travelled so far as the Thames. What notion could such waifs have of +a mountain, a valley, a cliff, or even of a rock? The value of the +optical lantern at once becomes apparent here. But better informed +children in high-class schools, although they see many places beyond +the London streets, can yet reap much advantage from the mode of +instruction which I am advocating; and as the range of knowledge +increases, so will some such means of illustration be forced upon +teachers. The labour and expense of tracing a dozen diagrams on glass, +in the way hereafter explained, is considerably less than that involved +in drawing a single large diagram for the schoolroom wall. By this easy +method the illustrations in any book can be roughly copied and rendered +available for an entire class. + +In the higher branches of knowledge the lantern can also give its help. +Botany, zoology, and natural history generally can be illustrated by +diagrams, photographs, and in many cases by natural preparations. The +revelations of the microscope can be transferred to the lantern, and +the most complex organisms can be seen clearly defined and magnified +many hundred times their natural size. It is possible, too, 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 way. +Let me cite for instance the formation of crystals, which can actually +be watched in progress, highly magnified, by the simple expedient of +smearing a piece of glass with a solution of sal ammoniac and placing +it in the lantern. There are several adjuncts which may be fitted to a +first-class lantern which I have not space to notice in detail. With +the lantern-microscope ordinary microscopic slides can be utilized, +and tanks for containing the living denizens of our ponds and ditches +may be employed. The marvels of polarised light may be demonstrated +with the lantern-polariscope. By another special device called the +‘aphengescope’ and which is made to fit on the lantern, opaque objects +can be thrown on the screen. It is possible, for instance, to utilize +ordinary photographs or diagrams on card, to show the moving works of +a watch, sections of fruit, and many other objects as explained in a +subsequent chapter. + +The lantern, at the time of exhibition, should stand firmly. It can, +if it be a small one burning oil, be placed on a box standing upon +a table. I myself prefer to place it on a photographic tripod-stand, +and this I effect by screwing on to the top of the stand a base-board +upon which the lantern firmly fits. For large lanterns, such as the +lime-light biunial, a far more solid arrangement is requisite. My own +method is this. The lantern screws on to the top of its travelling-box, +at the lower corners of which are sockets to admit four wrought-iron +legs. These legs are bent outwards, and what I may call their toes are +turned out, and have a hole into which a screw may be inserted and +driven into the floor. The lantern is fastened to the box by two hinged +pieces at the back, so that the nozzles can be raised to any extent +desired. + + + + +THE LIME-LIGHT. + + +The lime-light consists of a jet of mixed hydrogen and oxygen gases +under pressure, ignited, and forced upon a cylinder of lime, which it +renders white-hot. The heat given by these gases is second only to the +heat of the electric arc, and will melt that most refractory of metals, +platinum. Even the lime block cannot withstand the great heat to which +it is exposed, but is quickly pitted under the action of the flame. +Hence lime-light jets are furnished with an arrangement by which the +lime cylinder can be turned at frequent intervals, so as to offer a +fresh surface for the gases to play upon. + +There are three kinds of jet used for the lantern. Firstly, a jet in +which a stream of oxygen is forced through the flame of a spirit-lamp +on to a cylinder of lime. This form is perfectly safe, and although it +presents an immense improvement upon any form of oil arrangement, does +not afford sufficient light to illuminate a screen more than about nine +feet in diameter. Secondly, there is what is known as the blow-through +jet. In this case the jet is connected with the house gas, and the +oxygen meets it at the point of ignition, and is _blown through_ it on +to the lime. This form of jet is also safe; indeed, it is often called +‘the safety jet,’ and affords plenty of light even for professional +use. It is the one that I recommend the amateur to work with. Thirdly, +there is the mixed jet, in which the two gases in separate bags are +both under pressure, and mix together before reaching the external +orifice. This form of lime-light gives the most light of any; but such +care is requisite in dealing with it, that I shall say no more about +it, considering it unfit for casual acquaintance. + +A beginner might fancy that it would be a simple thing to mix the two +gases in one bag, put it under pressure, and use them thus. So it +would, and a beautiful light would be the result. Probably a beautiful +explosion would be another result, for the two gases mixed form a most +terrible compound, and a bag so charged would be almost equal in danger +to a live shell. + +With the spirit jet, or the ‘blow-through,’ the operator need have no +fear of danger. Oxygen is not an explosive, and, although the best +supporter of combustion, is not itself capable of being ignited. The +spirit jet I should not recommend, except in situations where coal gas +is not obtainable, so in my directions for using the lime-light, let it +be understood that I am considering the employment of the blow-through, +or safety jet. + +Let us suppose, then, that we are preparing for an exhibition. The gas +is made, and is at hand in the gas-bag; our lantern--and I will, for +simplicity’s sake, consider it a single lantern only--is raised on its +stand-table, or other support, at a convenient height from the ground, +and we wish to have a private rehearsal in order to see that all is +right. The first thing is to attach the hydrogen terminal of the jet, +marked H, by flexible tubing to the nearest gas-bracket. Now take a +cylinder of lime from its box, clear out the hole in the centre with a +bit of wire, or a match, and place it on the pin provided for it above +the jet. See that it turns freely, and so adjust the pin that the lime +is distant from the jet nozzle about the sixteenth of an inch. Light +the gas, and turn it down so that the flame is about an inch high. This +can be done with advantage an hour or more before the lantern is really +required, for the lenses and body of the lantern will by this means get +thoroughly warmed, and any moisture upon the glasses, which would show +as a blemish on the sheet, will be removed. + +In all cases the hydrogen should be lighted first, if only to +thoroughly warm the lime. Now the oxygen-bag can be put between the +pressure-boards, and connected by another tube to the tap marked O. +A half-hundred-weight having been put on the boards, the gas-bag tap +may be turned on to the full. We may now attend to the jet. Turn on +the hydrogen so that it flames up some inches over the lime, then +gradually turn on the oxygen. At first it is air only that comes away, +but presently with a characteristic little snap the two gases come +together, and the brilliant lime-light is produced. A little care in +adjustment of each tap alternately will soon show us the amount of gas +from each which will give the best result. + +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 lenses, or the +effect upon the sheet will be spoiled. The vertical movement of the +jet is governed by a little screw, which holds it to the post on which +it is fixed, which post stands upon an iron tray gliding between +grooves. We must raise or lower the jet until the right place is found, +when the screw can be brought home, and the jet is fixed. Even now, +most probably, we shall find that the outer margin of the disc is +ill-defined. This shows that the light is either too near or too far +from the condenser. By moving the jet on its tray bodily backwards and +forwards, we shall soon be able to find its correct position, and when +found, that position will hold good to the end of the exhibition. We +can now put a picture on the slide-stage, and focus it by means of the +screw on the front lens. If the lime is properly adjusted and centred, +our picture will be illuminated equally well in every part. + + + + +DISSOLVING VIEWS. + + +So far, we have considered the production of a brilliantly illuminated +picture with a single lantern. For many years after the lime-light +came into use, this was all that was required of it. But suddenly the +beautiful effect known as dissolving views was contrived--an effect +which, at the time of its introduction, made a wonderful sensation--and +the method of producing which was for a long time kept secret. The +old way of dissolving one picture into another, and the way which +must still be adopted if oil-lanterns are in question, was to use +two lanterns, side by side, and by a kind of see-saw arrangement in +front of the lenses, to gradually uncover one nozzle whilst the other +was being closed. This was easily done by furnishing each end of the +see-saw with a screen of tin, the edge of each being cut into teeth +like a comb. The one picture was thus caused to mingle with the other +until the first lantern was quite closed, when the new design became +perfectly disclosed. It soon became evident that the same effect could +be produced more simply and economically with the lime-light lanterns, +by contriving a special form of gas-tap which would slowly turn off +the gases supplied to one lantern, while it as slowly admitted the +gases to the other. By this arrangement nearly half the gas supply is +saved, and therefore very little more is wanted for a dissolving-view +apparatus than for a single lantern. + +Dissolving view, or biunial lanterns, as they are generally termed, are +now made in very compact form. The two systems of lenses, one above +the other--not side by side as of old--are fitted into one mahogany +case, lined with tin, and furnished with doors, so that the lights can +be tended when necessary. At the back of the arrangement is placed +the dissolving-tap, which is connected by indiarubber tubing with +the lime-jets, and has two nozzles by which the hydrogen and oxygen +respectively can be supplied to it. The dissolver is also furnished +with by-passes, so that when the gases are turned from one lantern, +just sufficient remains to keep the jet turned down ‘to the blue.’ + +The management of a pair of lanterns like this is, of course, much +more onerous than that of a single lantern; but when once understood +presents no difficulty. Before lighting up, be quite sure that all +connections--and there are many--are quite secure, and that each place +where indiarubber tubing fits on to metal is secured with twine. Now +light the hydrogen in both lanterns, which you can do by placing the +dissolving-tap in an upright position. Move the dissolver until the +upper jet seems on the point of going out; but prevent it doing so by +opening the hydrogen by-pass, and adjust this little tap so that the +flame remains about one inch high when the other lantern is being used. +Move the dissolver backwards and forwards a few times, so as to see +that it works well, and that the hydrogen flares up in each lantern +alternately. + +We can now pay attention to the oxygen supply. First see that the +bag is properly adjusted between the pressure-boards, and that the +weight--one 56 lb. weight is sufficient to begin with--is in its +place, above the upper board. Attending to the lower lantern first, +turn up the hydrogen, and very gently admit the oxygen by turning +the tap attached to the jet. When the light has been satisfactorily +established, the oxygen by-pass must be turned in the same way that the +other by-pass was just now treated, so as to admit a small amount of +gas passing to the lantern not in use. If this be not done, the sudden +inrush of the oxygen is sure to cause a small explosion, which will +blow the light out. This does not indicate any danger whatever, but is +inconvenient and undesirable during an exhibition. The upper lantern +may now be attended to with the same precautions; and if all has been +done well, the light will move from jet to jet alternately, as the +dissolver is worked. + +In using a double lantern, it is necessary to make both pictures +coincident on the sheet. If one picture overlaps the other at every +change, it has a most slovenly appearance. Such an error can be avoided +by manipulating certain screws fitted to the metal front of the +lantern, by which the two discs thrown upon the sheet can be adjusted +until they quite coincide. These screws allow the lower nozzle to be +pointed slightly upwards, and the upper one to point downwards, so that +the images cast by each may be made to meet at the screen. + +The double lantern is mainly employed for dissolving views; but its use +does not stop here. A great many beautiful “effects” can be compassed +by its means, a few of which I may here describe. Statuary slides form +very beautiful pictures if photographed direct from the marble; but +their effect is much enhanced if, by means of the auxiliary lantern, +a glow of colour is thrown upon the screen at the same time. A few +squares of differently tinted glasses, each mounted like an ordinary +slide, with a mask of oval or round shape, are all that is needed. +Again, a wintry scene in one lantern may be much improved by the effect +of falling snow, produced by working a special form of slide in the +other lantern. This slide consists merely of a frame containing a +roller at the top with the handle projecting outside. As the handle +is rotated, a long ribbon of black paper pierced with needle-pricks +is rolled up upon it, and each prick makes a descending spot of light +upon the screen, which together look exactly like falling snow. Sunset +and moonlight effects, windows lighted up in night-scenes, ripples +upon water, can all be managed by specially-devised ‘effect’ slides in +the second lantern. These effects can be much extended when a triple +lantern is employed; but as this instrument is not often found--out of +the hands of professional operators--we need not further allude to it. + +But the double lantern can be used with great advantage from an +educational point of view, in a manner that was first suggested by +the present writer. I mean in the demonstration of the main features +of Spectrum Analysis. Let me cite one example. A slide prepared and +coloured so as to represent the continuous solar spectrum, marked +with the principal _Frauenhofer_ lines, is placed, say, in the lower +lantern. We now wish to show the bright lines given by an incandescent +metal, say _sodium_. A slide, all blackened out but the double D +line due to sodium, and so placed on the glass that it will exactly +register with the D line in the coloured spectrum slide, is placed in +the upper lantern. The dissolver is now brought into play, and can be +so adjusted that while the continuous spectrum has all but faded away, +the two brilliant sodium lines stand out boldly in their proper place. +The spectra of all the other metals can be treated in exactly the +same manner, keeping the continuous spectrum in the lower lantern for +constant comparison and reference. + + + + +MAKING OXYGEN GAS. + + +There is very little danger incurred in the use of the lime-light +if only the operator be intelligent in its employment. But there +are certain dangers connected with the preliminary making of the +oxygen gas, so that that part of the work should only be entrusted +to a careful worker, and one who, knowing where the greatest care is +required, will take every precaution against disaster. I have myself +made several thousand feet of oxygen on different occasions, and have +never yet met with any mishap; but as I know of cases where serious +accidents have occurred, I have endeavoured to find out why they +have happened, and I now consider myself forewarned, and therefore +forearmed, against their repetition. The articles required for making +the gas comprise a retort in which to generate it, a gas-stove to +furnish the necessary heat, a wash-bottle or purifier, an indiarubber +gas-bag, and several feet of tubing. Beyond these is wanted the mixture +of chlorate of potash and peroxide of manganese in powder, which forms +the charge of the retort, from which the gas is generated on the +application of heat. + +I have found that the best proportions of chemicals to use are four +parts (by weight) of chlorate to one of manganese. Before being mixed +together, both should be most carefully picked over, and most probably +both will yield a small crop of bits of straw and wood-chips, which are +not only injurious, but would in sufficient quantity prove actually +dangerous if permitted to remain. The larger crystals of the chlorate, +and any lumps which may be found in the manganese, should be rubbed +down to powder by gentle pressure with the wooden spoon used for mixing +the compound, about two pounds of which will yield sufficient gas for +an evening’s show. The mixture can now be funnelled into the retort, +the nozzle of which, after being blown through to see that the passage +is clear, can be screwed into its place. + +The purifier, or wash-bottle, is made of tin, or may consist of +a wide-mouthed bottle with an indiarubber cap, fitted with inlet +and outlet tubes of metal or glass. In either case the vessel is +three-parts filled with water, the inlet tube dipping some inches below +the surface. This tube is subsequently connected by three or four +feet of indiarubber tubing with the retort. As the gas is given off, +it bubbles through this water, which not only cools it, but catches +the particles of solid matter which are sure to be blown from the +retort. The outlet tube is connected with the gas-bag. In the annexed +illustration the relative positions of the retort, purifier, and +gas-bag are shown, but in practice certain modifications are desirable. +It is as well, for instance, to stand a chair between the retort and +purifier, upon which the connecting rubber tube may rest, otherwise the +water evolved from the crystals of potash will condense in the tube +and obstruct the passage of the gas. Again, the gas-bag, instead of +being on the same level, should be laid on a table, so that any water +accidentally driven from the purifier may not be forced into it. The +rubber tubes should have an orifice of nearly half an inch, and should +on no account contain an inside coil of wire. Previous to making gas +the bag should be warmed for an hour or so in front of a fire, so as to +make it soft and pliable. The cock should then be opened, and the bag +rolled tightly up so as to expel any air. The tap should then be closed. + +[Illustration: FIG. 2. + +Diagram showing relative positions of _g b_, Gas-bag; _w b_, +Wash-bottle; and _r_, Retort.] + +When all is ready, and every junction made except that between the bag +and the pipe leading from the purifier, the gas-stove may be kindled, +but turned down almost to its lowest point. If this precaution be not +observed, the oxygen will come off with such rapidity as to be quite +out of control, and will probably blow the connections away. In two or +three minutes the gas will commence to bubble through the purifier, +at first intermittently, but the bubbling will gradually become more +regular, until it is evident that oxygen is coming over in earnest. The +brightening of a spark at the end of a blown-out match, held to the end +of the purifier-tube, will announce the fact that all the air has been +driven out of the pipes, and that gas has taken its place. Now is the +time to connect the gas-bag with the purifier. With a quick movement +the indiarubber tube should be slipped over the nozzle of the bag with +one hand, while the tap is turned on with the other. The gas should +now come over regularly until the bag is nearly half full, and this +will occupy about fifteen minutes. The action will then probably flag a +little, when the flame feeding the stove may be increased. When the bag +is nearly full the flame can be raised, if occasion should require, to +its utmost. + +Some care is requisite in finishing the operation. When the bag is +quite full and as tight as a drum, it should be disconnected before +anything else is done. Of course at the moment of taking the tube from +it, the tap must be turned. The next thing is to detach the retort +from the purifier _before the gas is extinguished in the stove_. This +is a most important point, for if the retort were cooled by putting +out the gas first, the water might be sucked into the retort from the +purifier, and a small steam-boiler explosion would be the result. In an +hour or so the retort will be cool enough to handle, when the nozzle +can be unscrewed and the vessel washed out with several changes of hot +water. It can then be dried and put away for the next occasion. The +retort-nozzle and its indiarubber tube should also be washed out, or it +may get clogged. + +Particular care must be taken to purchase the chlorate and manganese of +some reliable dealer. Accidents have been reported owing to lamp-black, +bone-black, etc., having been supplied in error for the manganese, +which is a black powder much resembling them. I find that the best +plan is to buy several pounds of each at a time, and to test a small +quantity of the mixed ingredients in a test-tube over a spirit-flame. +If the gas comes off with a slight sparkling of the ingredients all +is right; but if there is anything approaching to an explosion, the +manganese is at fault. One accident which I heard of was due to +connecting the retort to the wrong side of the purifier; the gas had +no outlet, and the retort exploded, breaking all the windows of the +room in which it was. + +Retorts are made either of copper or iron. I have tried both, and much +prefer the latter, which have also the advantage of being cheaper than +the copper ones. A good retort should serve for at least fifty charges, +and even then a new bottom can be put into it, and it will do duty for +another fifty. But no retort will last long unless properly treated. I +am quite satisfied that the spent charge if allowed to remain has the +effect of eating into the metal; it should, therefore, be washed out +soon after use. The thickness of a retort after much use can be gauged +by tapping it with the back of a knife when empty. + +The oxygen gas is most usually stored in an indiarubber bag. These +vary very much in quality, and the cheapest kinds are to be avoided. +The rubber should be soft and pliant, and should be covered outside +with stout twill. A good bag will almost last a lifetime if it be only +used occasionally. I have had one for many years, which looks shabby +enough with constant use, but seems to be as gas-tight and as efficient +generally as the first day I had it. Even then it had been in use for +some months by a friend. + +[Illustration: FIG. 3. + +Iron bottle for compressed oxygen gas.] + +A bag full of gas is not the most portable thing that could be named, +and various attempts have been made to replace it by some contrivance +of a more convenient character. There is, too, the danger of accidental +injury, which can readily occur if the bag is carelessly handled. In +very cold weather, for example, some bags get quite stiff and hard, +and have to be almost thawed before they can be used. Neglect of +this precaution will lead to cracks, which will eventually turn into +holes. 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 some, but are seldom used. Perhaps the +most convenient arrangement--which, however, is only suitable for a +single lantern--is to employ an iron bottle in which the oxygen is +greatly compressed. Such a bottle charged with gas can be obtained +from several dealers, and I have had some little experience of their +use. A bottle measuring three feet in length, and about seven inches +in diameter, will hold about eight feet of compressed gas--sufficient +for an ordinary evening’s work. At the end of the bottle is an opening +closed with a tap which can only be opened by a special form of key. +Into this orifice is screwed a nozzle, upon which an indiarubber tube +can be readily fitted. When a bottle of this kind is used, the amount +of oxygen which reaches the lime must be directly controlled by this +tap, and not by the tap attached to the jet, which must remain fully +opened. The reason of this is that the gas issues with such force, +that, unless controlled in the way I have stated, it will blow off +the tubing by its pressure. I found it so difficult to regulate the +supply, that I had an independent screw-tap made to fit on to the +bottle. This screw-tap is of the same pattern as those used on steam +engines to control the supply of steam to the cylinder, and with it +I can adjust the oxygen supply with the greatest nicety. My chief +objections to the bottle system--which presents many advantages in the +matter of portability--are, firstly, 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 +others; and secondly, you do not know how much gas you are using, +for you cannot see it diminish as you can when you employ a bag. For +these and other reasons I still prefer bags to store my gas, and shall +continue to do so until some improvement comes about. + +[Illustration: FIG. 4. + +Gas-bag and pressure-boards.] + +The gas-bag is wedge-shaped, and the thin edge of the wedge has in its +centre a gas-cock for the entrance and exit of the gas. The object +of the bag being in this form is, that it can conveniently be placed +between the pressure-boards. These, in their simplest form, consist +of two boards strongly put together--the size of the bag which is +used--which are hinged together at one end. At the centre of this +end, and between the hinges, is cut an oval opening through which the +gas-cock is thrust. A shelf on the upper board serves as a support for +the weights. At least two weights are required--one being sufficient +at first, when the bag is full; the other being added later on when +the pressure becomes reduced. 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 guarded, so that it is not accidentally +stepped upon. + +The lime-cylinders are sold in air-tight tin canisters holding one +dozen each. They are of two qualities--hard and soft. 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 used. But where only a small sheet has to be covered, and one gas +only is subjected to the unusual pressure, the soft limes will afford +perhaps a better light than the harder ones. Occasionally the lime, be +it hard or soft, will split. In such a case it ought to be immediately +replaced by a fresh one, otherwise the flame may possibly be diverted +towards the condensing lenses, and will fracture that nearest to the +light. It is advisable always to keep a spare lime within the lantern, +lying on the tray to which the jet is attached. By this means it gets +warmed, and ready for use if required. Lime is most absorbent of +moisture, and will, if kept where air can get to it, swell to double +its former size, and finally crumble to powder. For this reason the tin +canister containing the cylinders should have stretched over it, when +once opened, a broad indiarubber band which will cover the junction +between lid and box. If this precaution be neglected, the limes will +swell with a force sufficient to break the tin-containing vessel +asunder. A compressed lime cartridge, to which water is applied by +artificial means, has lately been successfully introduced to supersede +explosives hitherto used for mining purposes. This will show the +immense power of expansion of which the substance is capable. + + + + +THE SCREEN OR SHEET. + + +And now a word about the best form of screen or sheet for showing +lantern pictures upon. The best possible form of surface is a smooth +whitewashed wall; but as this is not commonly found among the +appointments of a sitting-room, where the lantern will be wanted, we +must find some substitute which will most nearly resemble it. A sheet +of cartoon paper, which can be bought of any length, and measuring more +than four feet across, will do well if only a small disc is desired. +The paper can be rolled up out of the way at a minute’s notice. If a +larger screen is wanted, it can be made of stout calico, faced with +white paper, and can be made to roll up and down like a school map of +large dimensions. A map-mounter, or even an upholsterer, would soon rig +up such an arrangement. + +There is a very effective way of showing small pictures and diagrams +with an oil-lantern, which I have more than once adopted, where a +room has been long in proportion to its breadth. This is to make a +wooden frame just large enough to take the full width of a sheet of +tracing-paper, and to put this screen between the lantern and the +spectators. Tracing-_cloth_ should be avoided, as it is so transparent +that the light streaming from the lens makes a blotch in each picture +when seen through it. + +If the lantern is brought into regular use--in a schoolroom, for +instance--it might be thought worth while to have a canvas sheet +whitewashed, and hung in the same manner that a stage drop-scene is +fixed. In making such a screen, the canvas should be tacked on a frame, +and should have a coating of thin glue, which should be allowed to +dry before two or more coats of whitewash are applied. It will be +understood that a really opaque screen, such as this represents, is the +more effective, because the light, instead of being partly lost--as +it must be in penetrating an ordinary calico sheet--is reflected and +utilized. + +But for public exhibitions on a large scale, the calico sheet is the +screen commonly in vogue, for it is conveniently put up and taken down, +and can be rolled into a bundle for easy transport. A sheet properly +hung should be as flat as a board and perfectly free from wrinkles +of any kind, and this can be accomplished without much difficulty by +adopting the following method, which is applicable to screens from +twelve feet square upwards. + +[Illustration: FIG. 5. + +Showing method of hanging a sheet.] + +The sheet should have at its top edge a strong cord sewn into its hem, +which cord should terminate at each side with a loop. On its sides and +bottom edges, the sheet should have brass curtain rings sewn on to it +at intervals of two feet. Having chosen the position of the screen, a +couple of screw-eyes are screwed into the roof, or cornice near the +top of the hall, at such a distance apart that the sheet can easily +go between them. Through each of these screw-eyes is passed a thin, +strong line, having at its end a clip like that commonly attached to a +dog’s chain. This clip is to clutch the loop of rope on each side of +the sheet. The sheet can now be pulled up into position: the free ends +of the cord being fastened to screw-eyes in the floor. It now merely +remains to lace with string the curtain rings on the side of the sheet +to the adjacent cord, and the arrangement is complete. The annexed +diagram shows the upper corner of such a sheet, with its attachments, +as just explained. Where the hall is of such a height that this plan is +not available, or where the stern custodians faint with horror at the +thought of their walls or ceilings being pierced with a screw-hole, the +same method can be carried out by fastening the screw-eye to a timber +upright on each side, supported by light struts. + +Some persons prefer a sheet stretched on a frame, and such a frame of a +very portable character can be easily devised. The frame itself is best +made of lengths of pine, about the size of broom-handles. These can be +joined together so as to make a frame of any reasonable dimensions, +by six-inch lengths of brass tubing. The same tubing, mitred into +L-pieces, will serve for the four corners. The sheet is furnished +with tapes to secure it to the frame, and the woodwork is kept in an +upright position by strong cords fastened by screw-eyes to the floor. +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 +side, and festoons of the same material above. + + + + +PICTURES FOR THE LANTERN. + + +Before the advent of the art of photography, pictures or slides for +the lantern were traced on glass and painted by hand; and this art +was carried to very great perfection. But no handiwork can equal +the productions of the photographic camera; so that when it was +found possible to produce transparent positives on glass, that could +be magnified on the sheet to any extent without deterioration, the +occupation of the artist on glass was almost gone. Photographs are now +almost exclusively used, and form, when properly executed, the finest +pictures for lantern use. The manner of their production is fully +described in my little book ‘How to Photograph;’ but as there may be +many would-be lanternists who do not care to dabble in photography, I +will here give a few plain directions by which lantern slides can be +extemporised. + +The standard size for lantern pictures is 3¼ × 3¼ inches. The glass +chosen should be as thin as possible, and quite free from scratches, +bubbles, or flaws of any kind whatever. Remember that a piece of the +finest hair which may well be overlooked upon the slide itself, will +appear on the screen as a huge snake. In like manner a tiny bubble in +the glass is magnified into a blemish the size of a soup-plate. Glass +presents a very difficult surface to draw or paint upon, particularly +if water-colours are employed, but by coating it with a transparent +medium in the first instance the difficulty is much reduced. A film +of plain collodion will, when dry, give a surface that can be easily +sketched upon with a fine pen and Indian ink. The sketch so made can +afterwards be filled in with water-colour, tempered with prepared +ox-gall, and taking care that the colours used are those which are +naturally transparent. Prussian blue, indigo, lake, the madders, +gamboge, burnt and raw Sienna, Vandyke brown, are all transparent +pigments, and will answer every purpose. Mixed with one another in +the manner detailed in any manual of water-colour painting, greens, +purples, and all secondary and tertiary tints are readily obtainable. + +Another method, and an easier one, for producing lantern slides was +introduced some years ago by the Rev. W. H. Dallinger; and although the +author of the method intended it for drawings of microscopic subjects +only, and with that idea brought it before the notice of the Royal +Microscopical Society, it will be readily seen that it is adapted to +all manner of lantern pictures. This method is best described in its +inventor’s own words: ‘On finely ground glass drawing with a black-lead +pencil is as easy as drawing upon cardboard. I get squares of glass +to suit the size of my lantern carefully ground on one side like the +focusing-glass of a camera.’ The author goes on to describe how, by +sketching upon the finely ground surface with a well-pointed hard +pencil--HH or HHH--and shading with a softer one, such as HB, capital +effects can be obtained. ‘If it be necessary to put in colour it may be +done, cleanly and carefully over the shading; thus one layer of colour +suffices. Now, of course, although we have a perfect drawing of the +object, with all the detail accurately given, it is not a transparency. +But we can easily make it one. Thin some good pale Canada balsam with +benzine to about the consistency of cream, and simply float it over +the ground surface of your glass; pour off until the drop comes very +sluggishly. Then reverse the glass so that the corner from which the +balsam was flowing off be placed upwards. Let the return flow reach +about the middle; then reverse it again, and move it in several +directions to get the balsam level. This may be done with a very little +practice, so that the surface shall be undistinguishable from glass. We +have now a perfect transparency. All that is required is twenty-four +hours for hardening (keeping the glass level), and then another square +of glass fastened on to it by strips of paper at the edges, with small +pieces of card at the corners to prevent contact, and it makes an +admirable lantern transparency.’ + +A hint about giving a fine grain to glass will not be out of place. +Upon a perfectly flat and firm table lay a piece of glass say six +and a half inches square, for this size can afterwards be cut across +into four lantern pictures. A sheet of wet blotting-paper under the +glass will keep it steady. Now pour upon its surface a mixture of +flour-emery and water. Place another piece of glass above, and work it +round with a circular motion, constantly spooning up the mud formed +by the emery and water, and which oozes out between the glasses, +and replacing it between them. In a short time both glasses will be +beautifully ground on the surfaces which have been rubbed together. A +moment’s consideration will show that the ground effect is produced +by the surface being broken up into innumerable tiny pits, each one +of which scatters the light. By Mr. Dallinger’s method of filling up +these pits with a glassy medium like Canada balsam, the glass is once +more presented with a flat surface, and therefore becomes once more +transparent. + +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 +degrees, with a sheet of paper underneath it to throw the light up +through the glass he is drawing upon. A good easel can be made of a +small frame--that belonging to a twopenny slate will do--attached to +a base-board, and supported on each side by struts. A ledge of wood +screwed across the frame makes a convenient support for the picture. +The annexed cut will sufficiently explain the arrangements described. + +[Illustration: FIG. 6. + +Glass easel.] + +And now a word or two about mounting the picture. As Mr. Dallinger +points out, a cover-glass should be provided, but it should be +prevented from actually touching the painted surface. This is best +brought about by using the masks cut out of black paper, and sold for +the purpose. A mask is inserted between the glasses, after which the +whole is fastened together by pasting a slip of paper round the edges +of the double glass, and turning it over on either side. Gum arabic +with twenty-five per cent. loaf-sugar added, is a good medium by which +to attach paper to glass. + +[Illustration: FIG. 7. Masks for lantern slides.] + + + + +ON THE COLOURING OF PHOTOGRAPHIC TRANSPARENCIES. + + +There are many amateur photographers nowadays who can produce fair +transparencies for the lantern, but at the same time there are many +possessors of a lantern who know nothing about the ‘black art.’ +Luckily for these, first-class pictures can be bought cheaply, their +average price ranging from eighteenpence to two shillings each. +Any optician’s catalogue will show what an immense variety of +subjects there is to chose from; not only can we obtain landscapes of +nearly every part of the world, but we can purchase figure studies, +copies of various pictures from books, maps, diagrams of scientific +matters--micro-photographs and statuary. These slides if coloured are +double the price of plain ones, and if very well coloured their price +is quadrupled. + +It would therefore be serviceable to many if they could learn how to +colour such pictures for their own use, and I give simple directions +how this can be accomplished. At the same time it is only fair to state +that the work is really difficult, and anyone to attain even slight +proficiency in slide-painting must devote a great deal of time and +patience to the subject. + +The photographic slide as sold consists of two glasses, one of which +bears the photograph. This is separated from the cover-glass by a paper +mask, the whole being bound round by a fillet of gummed paper. After +carefully cutting round this fillet the two glasses may be separated, +and the one bearing the picture is placed, varnished side upwards, upon +the glass easel, ready for colouring. Some colourists speak in favour +of water-colours for glass-painting, others prefer oil-colours, while +some, I understand, employ both on the same picture. I have tried each +system, and most certainly recommend oil-colours as being both easier +to work with, and doing more satisfactory work into the bargain than +water-colours. + +The materials required comprise ordinary oil-colours in tubes, of which +the following are perhaps the most useful that can be employed for the +purpose: + + Italian Pink. + Raw Sienna. + Yellow Lake. + Chinese Orange. + Brown Pink. + Prussian Blue. + Indigo. + Neutral Tint. + McGilp. + Brown Madder. + Rose Madder. + Purple Madder. + Crimson Lake. + Burnt Sienna. + Ivory Black. + +It is curious to observe that the suitability of these colours for +the particular purpose of glass-painting varies with the method of +manufacture. I find by experience that one maker’s Prussian blue is +better than another’s, while for a suitable crimson lake I have to go +to quite a different shop, and so on. + +The brushes used must be of the best, the majority of them being +camel-hair, a few fine sables being kept for special touches. It is +also necessary to provide some good large bushy camel-hair brushes to +be used as softeners. + +A flat porcelain palette is better than one of any other material, for +the strength of the tints is seen well, and the surface can easily be +cleaned with a little turpentine. A flexible palette knife must also be +provided. + +Dabbers to soften down skies and other flat masses of colour can be +made by wrapping a ball of cotton wool in fine wash-leather. The +leather should be first thoroughly washed with soap and water, and +it will be better if a little of the soap be left in it as it dries, +for this renders it soft and pliant. Both dabbers and brushes should +be kept in a dust-tight box, for dust is the greatest enemy of the +slide-painter. + +It will be noticed that the list of colours given includes those only +which are transparent, many others used in ordinary oil-painting being +omitted. It is obvious that opaque colours like Naples yellow or chrome +yellow would simply appear black on the sheet. The tyro who is used to +other methods of painting, and has some idea of the harmony of colours, +will, of course, have an immense advantage over anyone without artistic +knowledge or feeling; and when he has once mastered the technicalities +of the new work, will soon be able to produce passable pictures. The +list of colours given is necessarily limited for the reason already +given, but their number can be increased indefinitely by judicious +blending one with the other. Let me give a few instances. + +There is no green in the list given, simply because I do not know of a +good transparent one. But various tints of green suitable for foliage +can be easily made up with the colours named. Prussian blue mixed +with any of the yellows will at once give a crude green, but it will +not be suitable for use without the help of some other tint, such as +burnt Sienna, or one of the reds. Italian pink and indigo make a fine +green. Italian pink, brown madder, and Prussian blue is also another +useful combination. Brown pink, indigo, and Vandyke brown will be found +admirable for the shadows in foliage; indeed, the combinations for this +purpose are endless. Again, there is a difficulty generally found in +obtaining any approach to scarlet. The best I know of is a mixture of +Italian pink, crimson lake, and Chinese orange. For browns, Vandyke +brown, Chinese orange, ivory black, and burnt Sienna, will give any +range of tints, from the coldest to the warmest. The reader will soon +find by experiment the right proportions for mixing these colours to +produce the desired effect, and he will be much assisted in the work +by studying any good manual of water-colour painting. I recommend a +water-colour manual in preference to one dealing with oil-colours, +because the first deals more with transparent tints, which depend for +their effect upon the white ground upon which they are laid. In like +manner a lantern picture depends much upon the white surface upon which +the tints are subsequently exhibited. + +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 +Britain. This would seem to some an unimportant point, until they +remember that the skies and atmospheric effects seen in some other +lands would require an altogether different treatment. I once coloured +an Egyptian scene for a friend, and he admired my work, with one +exception. ‘You have given me an English sky,’ he said. The sky will be +the first thing to see to, and we will endeavour to give it a flat tint +of blue slightly darker at the zenith than it is at the horizon. We +squeeze out from its tube a little Prussian blue upon the palette, and +dipping a good-sized camel-hair brush into a small cup of turpentine, +we take up a little of the colour and work it about on the palette +until it seems of the right strength. Before applying it to the glass +we add to it a very small quantity of McGilp medium. Having mixed +this last addition with our brush-load of colour, we can apply it to +the glass, painting it in broad bands from side to side until the sky +is all striped with blue. If the subject comprises a range of distant +hills, let them too partake of the blue tint. When this is done, lay +aside the brush and let the coloured glass rest for a minute, so that +some of the turpentine will dry off. Now proceed to dab it carefully +with one of the leather dabbers. With a very light touch bring the +dabber down over and over again, and avoid anything like a rubbing +action. The movement must be vertical, and not in the least horizontal. +By bearing a little more heavily on the dabber as the horizon is +approached, the tint will be sensibly lightened. + +When this sky-colour has been uniformly dabbed in we may proceed to +put in, or rather wipe out, some cloud effects. A little piece of soft +kid wrapped round a pointed pen-holder is a good tool to use for the +purpose, but a leather stump will answer the same end. This part of +the work requires a little judgment and artistic taste. In a picture +full of detail and which only has a small portion of sky exposed, it +is best coloured simply blue. But where there is not much detail in +the landscape, as in the case for instance of a mill on a bleak moor, +the sky can be worked up with great advantage to the general effect. +The clouds are wiped out by a rubbing action combined with a dabbing +movement, so that the edges of the clouds formed remain quite soft. If +they appear too hard they can be corrected by a few gentle dabs with +the top of the finger. Before the leather is laid aside, it may be +employed for wiping off any portions of colour which have accidentally +been placed where they should not be. But if there is water included in +the subject, such as a lake or river, it will when the sky is reflected +in it partake of the same colour, and should be dabbed in at the same +time. + +We must now consider how we are going to treat the rest of our +picture. If there is some expanse of foreground it will make the best +contrast with the sky if we use a warm sandy colour. Chinese orange, +raw Sienna, and brown pink mixed in various proportions to suit the +lights and shadows of the picture will give the tint required. At this +stage, too, the middle tints of the composition lying between the sky +and the foreground can also be laid in. These will mostly consist of +subdued greys, made up of Prussian blue, burnt Sienna, purple madder, +and crimson lake. When these tints are all dabbed in, and the whole +picture has been carefully gone over with the leather point, so as to +remove truant colour, the slide may be laid aside to dry. I find it a +good plan to have a tin box containing grooves for this purpose. The +slides when grounded in in the way just described are placed in the +grooves, and the open box is turned towards a fire. In an hour or so +the colours are dry enough for further treatment. + +We can now once more view our work on the easel, and most probably +we shall see much to amend. The trees in the middle distance are too +yellow, or too blue. They are easily corrected by a touch of the tint +in which they fail. But at this stage of the painting we must use a +different medium for our colours. We have done with dabbing, and must +now lay the colours on as smoothly as possible with the brush alone. +Canada balsam in turpentine, of the consistence of very thin varnish, +is perhaps the best medium to use. It should be mixed with every colour +as it is taken upon the brush. + +The beginner will find some difficulty at first, particularly if +oil-colours are new to him, in keeping his brushes in order. He need +not have a brush for every tint. Let one be kept for skies, but only +two or three others are necessary. When I commence to paint a batch of +pictures I put on my table, after carefully dusting it all over with +a damp cloth, a sheet of newspaper. In the centre stands my easel. On +the left hand my colour-box, and on the right my palette. Close to the +palette is placed a double thickness of clean white tissue paper, and +a small pot of turpentine. When I wish to clean my brush, it is simply +dipped in turpentine, and drawn over the surface of the white paper +until I see that it leaves no trail of colour. By this simple means one +brush can be used for any number of tints, for the cleansing of it does +not occupy more than ten seconds. + +It is in the foreground of a picture that the artist must be lavish +with his bright colours. If the figures in the subject will allow of +bright colouring, so much the better; but it must be remembered that if +these colours are not put in with some regard to contrast, their effect +is much diminished, if not altogether lost. Let the painter remember +that the principal colours have their complementary colours, and that +wherever we can place one of these tints against its complementary, we +are bound to have harmony. Thus the complementary of blue is orange; of +red, green; and of yellow, purple. But for further particulars of this +nature, the aforesaid ‘Manual of Water-Colours’ must be studied. + +When the picture is apparently finished, it will, most likely, require +some finishing-touches. And here a new tool comes into use, namely, +the etching-needle. Take a pointed piece of wood, about the size of a +penholder, and bind upon it, by means of waxed thread, a good strong +sewing-needle, leaving not more than a quarter of an inch of the +point exposed. A few judicious touches with this needle will make a +vast difference in the effect of a picture, but anything like coarse +scratching must be avoided. The beginner will do well to view his work +in the lantern as it gradually progresses, for what may look very well +on the easel, will look very different when all its imperfections +are magnified on the screen. The art of slide-painting is one which +requires constant care and practice before anything like proficiency is +attained. + +In case some of my readers should be well acquainted with the +use of water-colours, and may be deterred from trying the art of +glass-painting because oils only are recommended for the work, I will +briefly describe how water-colours are utilized for slide-painting. +At the same time, I hold to my previously expressed opinion, that +oil-colours are the more suitable pigments to use. + +The varnished surface of a glass picture does not take kindly to +water-colour, 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 difficulty. By mixing each colour with a certain +proportion of prepared ox-gall the difficulty vanishes, 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 wool, before any colour is +applied at all. + +The same transparent colours as those recommended for oil-painting may +be employed, besides a few more transparent tints which are commonly +not ground up in oil. But the dabbers are of a different description. +Procure two or three good thick camel-hair brushes, and cut the hair +off straight with a pair of scissors, so as to leave the ends of the +hairs like a flat stump. Now carefully turn the brush round and round +in the flame of a spirit lamp, or candle, so as to just singe the +point of each hair. When this is done, rub the ends of the hair on the +finest glass-paper until every trace of singeing has disappeared. This +treatment will leave the brush with a flat woolly head like a mop, +which makes an excellent dabber. + +When the sky-colour has been applied as evenly as possible, and has +been allowed to dry, the surface may be worked over with the dabber. +But, before doing this, gently breathe over the colour. The dabber will +remove little particles of the pigment, and will reduce the general +strength of the tint, so that this loss should be provided for when +the colour is first applied. Clouds, etc., can be wiped out with the +leather, after the breathing operation, and in many other respects the +two modes of colouring agree. + +When the general tints have been laid in, the colours may receive a +coat of mastic varnish, and this again can be worked over with colour +to strengthen those tints which may require it. The varnish also +confers a transparency upon the tints that they do not possess without +it. + + + + +SHOWING SOLID & OPAQUE OBJECTS ON THE LANTERN SCREEN. + + +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 ways. Transparent preparations have the light thrown +through them by means of the adjustable mirror beneath the stage. +Opaque objects, on the other hand, must have light thrown upon them +from above, and this is managed by means of a separate condensing lens. +For the magic lantern, transparent pictures are almost wholly employed; +but there is a means of utilizing paper prints, photographic _cartes de +visite_, and a certain limited number of solid objects, so that they +may be shown in an enlarged form on the sheet. The effect is not so +bright as when transparencies are employed, for a large proportion of +the available light is absorbed in the operation; but there are many +who would sacrifice a good deal in the way of effect, for the undoubted +advantage of being able to utilize the contents of their albums, etc. + +[Illustration: FIG. 8. Ground-plan of Chadburn’s Opaque Lantern. + +_p_, Picture; _c_, Condenser; _l_, Light; _r_, Reflector; _o_, +Objective.] + +The first instrument which was constructed to accomplish this end is +known as Chadburn’s lantern; and, as will be seen from the annexed +diagram, it differs very much from the ordinary form of magic lantern. +From what has been already said concerning the loss of light, it will +be evident that a powerful luminant is a matter of prime consideration. +A good oil-lantern will do the work--but not so well as the lime-jet. +The luminous face of the lime, instead of being turned towards the +optical system, is opposite a concave reflector placed at the back of +the lantern. From this the light is reflected towards the condenser, +which condenser concentrates the light obliquely upon the object. The +picture or object is contained in a kind of box joined to the main +lantern, and which holds immediately opposite the illuminated picture +the lens for projecting its image upon the screen. This pioneer form +of opaque lantern has been superseded by the instrument called the +Aphengescope. This can be purchased now of most opticians. 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 lantern. + +The aphengescope can be used for showing woodcuts, paper photographs, +printed and written matter of any kind, so long as the space covered is +within the size of the instrument. Thus any caricatures from our comic +publications could be pasted on card, and enlarged by its means. But it +will be readily observed that this class of subjects, if photographed +as transparent positives and used in the ordinary lantern, can be shown +far better. The principal use of the aphengescope is to show solid +objects which cannot by any possibility be shown enlarged without its +help. + +Let us suppose, for instance, that it is desired by some collector +to show his friends a cabinet of coins and medals. Such objects are +so bright in themselves that they are admirably adapted to this +instrument. Their form, colour, and minute markings are faithfully +reproduced; whilst the raised portions catch the reflected light +in such a way as to make the images look as solid as the objects +themselves. At the Polytechnic Institution, a lecture upon the +invention of the watch, and its gradual development, was beautifully +illustrated by the opaque lantern. First came the different parts of +the watch, and then the varied movements. It was most curious and +instructive to see the wheels and springs all in movement upon the +screen. + +There are also many natural things which can be shown by the same +means. A freshly opened oyster makes a very remarkable object. A +still more curious effect is obtained by concentrating the light +upon a freshly cut orange or lemon. When the fruit is squeezed, the +pips and juice appear to fly upwards; for, of course, everything is +shown upside down, as in the ordinary lantern. The opaque lantern was +once introduced into a court of law in America, as a witness for the +prosecution in a case of forgery. The following is a condensed account +of the occurrence, taken from a New York paper: + +‘During the recent trial, it became necessary to show the differences +between a genuine signature and an imitation or forgery of the +same. For this purpose, there was brought into court a powerful +reflecting magic lantern. The room was darkened, and images of the +two signatures, enormously magnified, were thrown side by side upon +a screen before the judge and jury. The false signature was at once +revealed. The illumination of the writing was effected by means of +two powerful lime-lights contained within the lantern. The peculiar +arrangement of the lights and screen enables the examiner to discover +the surface of the paper through the ink, so that patching, shading, +or painting of letters becomes evident the instant it is brought +under the focus of the lantern. An arrangement of screens, by which +the light is cut off alternately from either side of the instrument, +discovers any tampering with the surface of the paper, either by +scratching or washing by chemicals. (In other words, by throwing the +light alternately from either side, the relief caused by the grain of +the paper is clearly shown; and any tampering with that relief, by +scratching or otherwise, at once becomes apparent.) The instrument, in +this case, was of sufficient capacity to view at once two bank-notes +placed side by side, and the pictures were of such fineness that there +was no difficulty in viewing their smallest details. 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 expert, with the help of a microscope, would answer the +same end. + +Under the name of the Physioscope, an immense opaque lantern was +exhibited some years back in London. The object magnified on the +sheet was the human face, and a correcting lens was included in the +apparatus, so that the face was seen right way up. It was always rather +an unhappy face, for the individual who lent his countenance to the +transaction had on either side of him, and within a few inches of his +cheeks, a very powerful lime-light, the heat and glare from which were +sufficient to render anyone uncomfortable who was not a salamander. + + + + +THE LANTERN MICROSCOPE. + + +Of late years it has become possible to take very beautiful photographs +of microscopic objects, which, when used as lantern-slides, give a very +fine effect. Numerous slides of this character may now be purchased, +which cover a vast field of microscopic knowledge, and many will be +content with what they can thus obtain. But there is another class +of workers who, perhaps possessing a large number of microscopic +slides, will be glad to utilize them for the lantern, so that they +are no longer limited to the individual eye. For these the lantern +microscope, which will screw in front of the lantern in place of the +usual optical system, is a most useful instrument. Different makers +advertise in their catalogues lantern microscopes which range in +price from twenty-five shillings to as many guineas. 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 £150 +each. The amateur lanternist will, therefore, have some difficulty in +deciding what he ought to pay for such an instrument. And it is most +difficult to advise him on that point. His best plan is, perhaps, to +see for himself what the makers can offer him, and, if possible, to +seek a trial of the instrument before he purchases it. + +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 it. The objective lenses +were uncorrected, and small in aperture, so that the instrument was +far from being a perfect one. But the intensity of the solar light +covered many objectionable features, and it was possible to get +some astonishing effects with the contrivance. But sunlight is such +an uncertain commodity in our climate that, when the lime-light came +into prominence, the old solar microscope was forgotten in favour of +that which depended upon a more constant, if a far less intense, light +source. + +The great difficulty to overcome in the lantern microscope is to get +the light sufficiently intense to well illuminate the objects. The +aperture of a microscope objective, even of low power, is so small, +that, when the pencil of light which it emits is spread over a screen, +the light is so attenuated that the details of the object are difficult +to make out. In the near future, when we are promised that electricity +shall be laid on to our homes, as gas is now supplied to us, the +difficulty will disappear, for the electric-arc light is many times +more intense than the most powerful lime-jet. + +Having obtained a lantern microscope, the next thing to consider is the +class of objects which can best be shown with it. To help the reader in +determining this point, I will now give a kind of sketch of a popular +lecture to accompany an exhibition of the instrument. + +Such a lecture might usefully commence with a brief description of +the microscope: its history, and how, in its improved form, it has +opened up a world of minute life, of which our forefathers could have +had no conception. We might then put forward a few remarks as to the +adaptation of the microscope to the oxyhydrogen lantern, and point out +how by its aid a number of persons can at the same time see what, in an +ordinary microscope, is visible to only one person. So much by way of +introduction. + +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 Nature: the Mineral Kingdom, the +Vegetable Kingdom, and the Animal Kingdom. Show how one is dependent +upon the other, and the difficulty in many cases of drawing a line to +separate the minute organisms of the Animal Kingdom from those of the +Vegetable World. Numerous examples from the lower forms of life may be +quoted to illustrate this. Now show and explain subjects from each of +the three divisions, taking the minerals first. Define a mineral, and +show how they crystallize in definite forms. Illustrate the process +of crystallization by putting a drop of a saturated solution of +sal-ammoniac on a slip of glass, and spreading it over with a brush. +Such a glass placed in the microscope will, as it dries, become covered +with branches of crystals, which seem to grow and strike out in various +directions on the sheet in a truly marvellous manner. Sections of +various minerals may next be shown, finishing with sections of coal. In +pointing out the origin of coal from plants, we may easily drift into +the next division of our subject--the Vegetable Kingdom. + +Here we have indeed a wide field to illustrate. Commencing from the +simple cell, as exhibited, for instance, in a bit of so-called green +mould, and arriving gradually at sections of different stems of plants +(which by the way form most beautiful objects on the screen), sections +of different woods, parts of flowers, etc. From these it will be easy +to step over the indistinct boundary-line which separates us from the +Animal World. Here we can commence with the lowest organisms; next +show the living inhabitants of our ponds and ditches. Arrive at the +Insect World, and show the generally unfamiliar parts of familiar +insects--bees, wasps, flies, etc. We can then go higher, and exhibit +sections of bone, hair, etc.; finishing with the structure of the human +body, so far as it can be indicated by means of the microscope. This +is a brief sketch of the kind of entertainment the microscope is able +to afford, which can be modified to suit the views of the exhibitor. + + + + +MECHANICAL OR MOVING-PICTURES. + + +The most common form of moveable slide is that known as a ‘comic slip.’ +This mechanical contrivance for the amusement of youth is generally of +the coarsest execution, 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 improvement. The ‘comic slip’ consists of +a glass in a wooden frame, with another loose piece of glass which +can work backwards and forwards in front of it. This movable glass +generally serves as a mere screen to cover something painted underneath +it, and it is rubbed over with black varnish so as to be opaque. Thus +a gentleman is represented with a nose of the normal size, but as the +screen is withdrawn it elongates to an awful extent. Or a woman’s +tongue may be graphically, if not elegantly, portrayed in the same +manner. + +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 attachment. A +common design for this device is a landscape with a windmill in the +centre. The sails of the mill are painted on the revolving glass, and +can be kept in rotation as long as desired. The chromatrope effect +is managed in the same way, only that in this case both glasses are +caused to slowly revolve in reverse directions. There are many people +who admire chromatropes, and many others who regard them as rather +trying to the eyes. Rippling water, the rising or setting of the sun +or moon, and astronomical slides illustrative of the movements of the +heavenly bodies, are among the subjects which can be well illustrated +by mechanical means. + +Perhaps the cleverest piece of apparatus ever invented to give +the effect of movement by means of a magic lantern is Beale’s +choreutoscope. This instrument depends upon the well-known phenomenon +common to our eyes, called persistence of vision. 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 lens, which is placed behind the pupil. +So far, the human eye resembles a camera obscura. Persistence of +vision means that an image so cast upon the retina remains impressed +there for about the eighth part of a second. For this reason we wink +continually without knowing it, for the light impression remains with +us during the short time that the eye is closed in accomplishing that +necessary action. A burnt stick with a red-hot end whirled round and +round appears to us like an unbroken circle of fire. The separate drops +of rain as they fall from the sky look like streaks of water, and so +an artist will represent them in his picture. A quickly moving meteor +looks like a long trail of fire for the same reason. + +In the choreutoscope we have a very elegant adaptation of the same +principle. It consists, in its commercial form, of a slide arrangement +that can be placed in any lantern. This contains a narrow strip of +glass, with, say, six figures painted upon it, each figure having a +different position. A dancing man is a good representative of the rest. +By a turn of a handle each figure is brought into view successively, +but so rapidly as to give the effect of moving arms and legs. An +interceptor or screen runs in front of each figure as the change occurs. + +One of the best designs made for this instrument is a dancing skeleton +(see annexed cut). In this case the figures are cut stencil-fashion +out of very thin brass, 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 manner. The choreutoscope is not only a +most amusing contrivance, but it illustrates in a very beautiful manner +this optical law called ‘persistence of vision.’ + +[Illustration: FIG. 9. Facsimile of a dancing skeleton for Beale’s +Choreutoscope.] + + + + +CONCLUDING REMARKS. + + +The best lantern and the best pictures will not interest an audience +unless the entertainer or lecturer is up to his work, and the matter +which he conveys is skilfully put together. 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 ‘lecture’ is to them as a red rag is to a +bull. When I say incompetent men, I do not mean uneducated ones; but I +mean those who from natural want of voice, and utter ignorance of its +management, are generally unfit for public speaking. 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 is, without any +previous knowledge or practice, fit to lecture on the particular +subject with which his name is identified. Or his claims to recognition +as a lecturer are based upon certain cabalistic letters after his name, +which in many cases represent only so many guineas yearly subscribed to +those who confer them. Lecturing is an art that can only be acquired +successfully by those who have certain qualifications for the work, +and among these the foremost is the power of imparting knowledge to +others in a common-sense and interesting manner. Luckily for him, the +amateur lecturer is likely to meet with a far more indulgent audience +than those which professional men have occasionally to face; but this +is no reason why he should be careless as to his method of delivery, +or of the matter delivered. Perhaps the er--worst fault er--which a +lecturer can er--fall into--is the one indicated er--in this sentence. +‘To _err_ is human,’ in a wider sense, unfortunately, than Pope, the +writer of that well-known line, ever dreamt of. Unless a would-be +lecturer can conquer this tiresome habit, or any other trick of speech +which he may have cultivated, by all means let him confine himself to +the management of the lantern while some one else acts as showman. + +If two people are thus managing an exhibition between them, and if +the room be large, so that they are widely separated, some signal +from the lecturer to indicate that he wants the next picture thrown +on the screen becomes necessary. A bell, or anything that makes a +noise, is distracting both to lecturer and audience. Still worse are +verbal instructions from one to the other. I myself use an electric +single-stroke bell with the gong removed, the hammer of which gives +a little click unmistakable to the operator, but quite unheard by the +audience. Such a bell can be placed close to the lantern, while its +push is far away on the lecturer’s desk. Sometimes a string can be +carried from lecturer to operator, a gentle pull of which will give the +necessary signal. Some lecturers signal by uncovering a little pane +of red glass in the back of their reading-lamp. But I think that any +sight signal is inadmissible, because the operator has quite enough +to do in attending to his duties without having his attention thus +distracted. The signal, of whatever nature it be, should be given by +the lecturer some seconds before he has finished with the picture in +hand, otherwise there is an awkward pause while the operator makes the +necessary change. Before the lecture begins, the reader should make +himself not only thoroughly familiar with his subject, but should be +also familiar with the different pictures which illustrate it. 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 repute, and are in every way excellent. Let +him, then, carefully go through the reading beforehand, comparing each +picture with the text, and making himself so familiar with its details +that he is afterwards able, during performance, to point out anything +to which attention may advantageously be directed. Particularly is +this necessary in the case of an introductory map, where places of +importance to the subject in hand must be pointed out. The most +convenient form of pointer, by the way, is a Japanese fishing-rod, +which telescopes into small compass when not in use. + +For an evening’s lantern entertainment to be successful, a great deal +depends upon the operator. With a mineral-oil lamp in a small room, his +duties are not very onerous, for the lamp when once established should +require no further attention, except it be to turn down a wick which +shows symptoms of smoking. But he should be careful to have in reserve +a glass or two to replace the front glass of the combustion-chamber, +which may crack through some unexpected draught of air. His slides must +all be numbered and in order. They may be each mounted in a wooden +frame to fit the lantern stage, or else the lantern may be fitted +with a permanent grooved slide in which the glass pictures are placed +one after another, the last one pushing out the one before. Another +plan, which is a good one to adopt where a single lantern only is +being used, is to make use of what is called a panoramic slide. It is +constructed like the one just described, only it is furnished with a +travelling tape upon which each picture rests. The turn of a handle +moves the tape, and the pictures travel forward panorama-fashion. + +In the use of a double lantern furnished with lime-jets, there is +plenty for two hands to do, for the operator has to keep his attention +fixed not only upon the business of changing the pictures, but upon the +condition of the lights. As the pressure of the oxygen gas varies as it +is gradually consumed, so the supply of the two gases to the jets will +want constant adjustment if the maximum quantity of light is expected. +Extra weights, too, must be added as the pressure-boards gradually sink +down. Beyond carefulness in this respect, the lantern operator must see +to the occasional turning of his limes, taking care to do this when +the lime wanting attention is not in actual use. He should also find +time to wipe the glass of each picture with a leather before putting +it in the lantern, for a film of moisture condenses on the surface, +particularly in a room full of people. + +The success of a lantern entertainment depends nearly as much on the +competence of the assistant as it does on the powers of the lecturer. +I am perhaps fastidious on this point, for my lecturing apprenticeship +was served at the late Royal Polytechnic Institution, where operators +were employed who had spent the best part of their lives in this +particular work. It was seldom, indeed, that they made a mistake. + + +THE END. + + +BILLING AND SONS, PRINTERS, GUILDFORD. + + + + + Transcriber's Notes: + + Italics are shown thus: _sloping_. + + Variations in spelling and hyphenation are retained. + + Perceived typographical errors have been changed. + + + +*** END OF THE PROJECT GUTENBERG EBOOK 75890 *** |