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| committer | nfenwick <nfenwick@pglaf.org> | 2025-04-17 11:21:02 -0700 |
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diff --git a/75890-h/75890-h.htm b/75890-h/75890-h.htm new file mode 100644 index 0000000..bf24b2b --- /dev/null +++ b/75890-h/75890-h.htm @@ -0,0 +1,2660 @@ +<!DOCTYPE html> +<html lang="en"> +<head> + <meta charset="UTF-8"> + <title> + The Magic Lantern | Project Gutenberg + </title> + <link rel="icon" href="images/cover.jpg" type="image/x-cover"> + <style> + +body { + margin-left: 20%; + margin-right: 20%; +} + + h1,h2 { + text-align: center; /* all headings centered */ + clear: both; +} + +h1 {font-weight: normal; + font-size: 240%; + margin-top: 2em; + word-spacing: 0.3em; + } + +h2 {font-weight: normal; + font-size: 130%; + margin-top: 2em; + word-spacing: 0.3em; + } + +p { + margin-top: .51em; + text-align: justify; + margin-bottom: .49em; +} + +.p2 {margin-top: 2em;} +.p4 {margin-top: 4em;} + +hr { + width: 33%; + margin-top: 2em; + margin-bottom: 2em; + margin-left: 33.5%; + margin-right: 33.5%; + clear: both; +} + +hr.full {width: 95%; margin-left: 2.5%; margin-right: 2.5%;} + +hr.r65 {width: 55%; margin-top: 0em; margin-bottom: 0em; margin-left: 22.5%; margin-right: 22.5%;} + +div.chapter {page-break-before: always;} +h2.nobreak {page-break-before: avoid;} + +table { + margin-left: auto; + margin-right: auto; +} + +.tdl {text-align: left;} +.tdr {text-align: right;} +.tdc {text-align: center;} +.tdrb {text-align: right; vertical-align: bottom;} + + +.pagenum { /* uncomment the next line for invisible page numbers */ + /* visibility: hidden; */ + position: absolute; + left: 92%; + font-size: small; + text-align: right; + font-style: normal; + font-weight: normal; + font-variant: normal; + text-indent: 0; +} /* page numbers */ + + +.caption {font-size: 80%; + text-align: center;} + +.up {font-size: 160%;} +.xlarge {font-size: 140%;} +.large {font-size: 120%;} +.less {font-size: 90%;} +.more {font-size: 80%;} +.med {font-size: 70%;} +.mid {font-size: 60%;} + +.c {text-align: center;} + +.sp {word-spacing: 0.3em;} + +.lsp {letter-spacing: 0.2em;} + +.oldeng {font-family: "Old English Text MT", serif;} + +.ph2 {text-align: center; text-indent: 0em; + font-size: 130%; + margin-top: 1em; + word-spacing: 0.3em; + letter-spacing: 0.2em;} + +.r {text-align: right; + margin-right: 2em;} + +.l {text-align: left; + margin-left: 2em;} + + +.smcap {font-variant: small-caps;} + + +/* Images */ + +img { + max-width: 100%; + height: auto; +} +img.w100 {width: 100%;} + + +.figcenter { + margin: auto; + text-align: center; + page-break-inside: avoid; + max-width: 100%; +} + +.figcenter1 { + padding-top: 2em; + padding-bottom: 2em; + margin: auto; + text-align: center; + page-break-inside: avoid; + max-width: 100%; +} + + +/* Transcriber's notes */ +.transnote {background-color: #E6E6FA; + color: black; + font-size:small; + padding:0.5em; + margin-bottom:5em; + margin-top:3em; + font-family:sans-serif, serif; + border: .3em double gray; + padding: 1em; +} + + </style> +</head> +<body> +<div style='text-align:center'>*** START OF THE PROJECT GUTENBERG EBOOK 75890 ***</div> + +<div class="figcenter"> +<img src="images/cover.jpg" alt="cover"> +</div> + + + + +<h1> +THE MAGIC LANTERN</h1> + +<p class="c sp xlarge"> +<i>AND ITS MANAGEMENT</i></p> + +<p class="c p4 more"> +INCLUDING</p> + +<p class="c sp less"> +<i>FULL PRACTICAL DIRECTIONS FOR PRODUCING THE LIME<br> +LIGHT, MAKING OXYGEN GAS, AND PREPARING<br> +LANTERN SLIDES</i></p> + +<p class="c p4 more"> +BY</p> + +<p class="c sp lsp xlarge"> +T. C. HEPWORTH</p> + +<p class="c sp mid"> +LATE LECTURER ON SCIENCE TO THE ROYAL POLYTECHNIC<br> +INSTITUTION, LONDON.</p> + +<div class="figcenter1"> +<img src="images/fig1.jpg" alt="decoration"> +</div> + +<p class="oldeng c large"> +London</p> + +<p class="c sp xlarge"> +CHATTO AND WINDUS, PICCADILLY</p> + +<p class="c"> +1885</p> + +<p class="c"> +[<i>All rights reserved</i>] +</p> + + + +<hr class="full x-ebookmaker-drop"> + +<div class="chapter"> +<p class="ph2">PREFACE.</p> +</div> + + +<p><span class="smcap large">During</span> 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.</p> + +<p class="r large"> +<span class="smcap">T. C. Hepworth.</span></p> + +<p class="l"> +<span class="smcap">32, Cantlowes Road,<br> +      London, N.W.</span> +</p> + + +<hr class="full x-ebookmaker-drop"> + +<div class="chapter"> +<p class="ph2">CONTENTS.</p> +</div> + + +<table> + +<tr> + <td class="tdc"><a href="#c1"><span class="smcap">The History of the Magic Lantern.</span></a></td> + <td class="tdr"></td></tr> + +<tr> + <td class="tdl"></td> + <td class="tdr"><span class="mid">PAGE</span></td></tr> + +<tr> + <td class="tdl">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</td> + <td class="tdrb">1-12</td></tr> + +<tr> + <td class="tdc"><a href="#c2"><span class="smcap">The Lime-Light.</span></a></td> + <td class="tdr"></td></tr> + +<tr> + <td class="tdl">Different forms of lime-jets.—Precautions to be observed +in their use</td> + <td class="tdrb">12-16</td></tr> + +<tr> + <td class="tdc"><a href="#c3"><span class="smcap">Dissolving Views.</span></a></td> + <td class="tdr"></td></tr> + +<tr> + <td class="tdl">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</td> + <td class="tdrb">17-22</td></tr> + +<tr> + <td class="tdc"><a href="#c4"><span class="smcap">Making Oxygen Gas.</span></a></td> + <td class="tdr"></td></tr> + +<tr> + <td class="tdl">Necessary precautions.—The purifier.—Explanatory +diagram.—Practical details.—The retort.—The +gas-bag.—Iron bottle for compressed gas.—Pressure-boards.—Lime +cylinders</td> + <td class="tdrb">22-33</td></tr> + +<tr> + <td class="tdc"><a href="#c5"><span class="smcap">The Screen or Sheet.</span></a></td> + <td class="tdr"></td></tr> + +<tr> + <td class="tdl">Arrangement adapted to a sitting-room.—Public exhibitions.—Method +of hanging a large sheet.—Sheets +on frames</td> + <td class="tdrb">33-37</td></tr> + +<tr> + <td class="tdc"><a href="#c6"><span class="smcap">Pictures for the Lantern.</span></a></td> + <td class="tdrb"></td></tr> + +<tr> + <td class="tdl">Photographic slides.—Home-made pictures.—Drawing +pictures on ground-glass.—The slide-painter’s +easel.—Mounting slides</td> + <td class="tdrb">37-43</td></tr> + +<tr> + <td class="tdc"><a href="#c7"><span class="smcap">On the Colouring of Photographic Transparencies.</span></a></td> + <td class="tdrb"></td></tr> + +<tr> + <td class="tdl">The process described.—Oil-colours employed.—Apparatus +required.—Mixed tints.—How to lay on the +colour.—Finishing touches.—Painting in water-colours</td> + <td class="tdrb">43-55</td></tr> + +<tr> + <td class="tdc"><a href="#c8"><span class="smcap">Showing Solid and Opaque Objects on the Lantern<br> +Screen.</span></a></td> + <td class="tdrb"></td></tr> + +<tr> + <td class="tdl">Chadburn’s opaque lantern.—The aphengescope.—Showing +coins, medals, etc.—The opaque lantern +in a law court.—The physioscope</td> + <td class="tdrb">56-61</td></tr> + +<tr> + <td class="tdc"><a href="#c9"><span class="smcap">The Lantern Microscope.</span></a></td> + <td class="tdrb"></td></tr> + +<tr> + <td class="tdl">Photographic microscopic slides.—The solar microscope.—A +sketch lecture </td> + <td class="tdrb">61-65</td></tr> + +<tr> + <td class="tdc"><a href="#c10"><span class="smcap">Mechanical or Moving Pictures.</span></a></td> + <td class="tdrb"></td></tr> + +<tr> + <td class="tdl">Comic slips.’—Beale’s choreutoscope.—The dancing +skeleton</td> + <td class="tdrb">66-69</td></tr> + +<tr> + <td class="tdc"><a href="#c11"><span class="smcap">Concluding Remarks.</span></a></td> + <td class="tdrb"></td></tr> + +<tr> + <td class="tdl">The management of the lantern in public.—Signals +between lecturer and operator</td> + <td class="tdrb">70-75</td></tr> + + + +</table> + +<hr class="full x-ebookmaker-drop"> + +<div class="chapter"> +<p><span class="pagenum" id="Page_1">[Pg 1]</span></p> + +<h2 class="nobreak" id="c1"><span class="up">THE MAGIC LANTERN</span></h2> +</div> + +<p class="c large"><i>AND ITS MANAGEMENT</i>.</p> + + +<p><span class="smcap large">There</span> 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.</p> + +<p>With regard to the early history of this<span class="pagenum" id="Page_2">[Pg 2]</span> +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.’</p> + +<p>But from this time a gradual improvement +began. First, the old oil-lamp was replaced by +the argand burner; then came gas; finally<span class="pagenum" id="Page_3">[Pg 3]</span> +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.</p> + +<p>During the past few years two circumstances +have combined to render the optical lantern<span class="pagenum" id="Page_4">[Pg 4]</span> +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.</p> + +<p>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.</p> + +<div class="figcenter"> +<img src="images/fig2.jpg" alt="lenses"> +<p class="caption"><span class="smcap">Fig. 1.</span></p> +<p class="caption">L, Light; <i>c</i>, <i>c</i>, Condensing lenses; <i>o</i>, <i>o</i>, Objective lenses.</p> +</div> + +<p>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 +<span class="pagenum" id="Page_5">[Pg 5]</span>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<span class="pagenum" id="Page_6">[Pg 6]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_7">[Pg 7]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_8">[Pg 8]</span> +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.</p> + +<p>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.</p> + +<p>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<span class="pagenum" id="Page_9">[Pg 9]</span> +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.</p> + +<p>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.</p> + +<p>The schoolmaster of a London Board +School once told me of some of his difficulties<span class="pagenum" id="Page_10">[Pg 10]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_11">[Pg 11]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_12">[Pg 12]</span> +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.</p> + + +<hr class="full x-ebookmaker-drop"> + +<div class="chapter"> +<h2 class="nobreak" id="c2">THE LIME-LIGHT.</h2> +</div> + + +<p>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<span class="pagenum" id="Page_13">[Pg 13]</span> +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.</p> + +<p>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 <i>blown through</i> 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<span class="pagenum" id="Page_14">[Pg 14]</span> +shall say no more about it, considering it unfit +for casual acquaintance.</p> + +<p>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.</p> + +<p>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.</p> + +<p>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.<span class="pagenum" id="Page_15">[Pg 15]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_16">[Pg 16]</span> +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.</p> + +<p>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.</p> +<hr class="full x-ebookmaker-drop"> + +<div class="chapter"> +<p><span class="pagenum" id="Page_17">[Pg 17]</span></p> + +<h2 class="nobreak" id="c3">DISSOLVING VIEWS.</h2> +</div> + + +<p>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<span class="pagenum" id="Page_18">[Pg 18]</span> +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.</p> + +<p>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.’</p> + +<p>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<span class="pagenum" id="Page_19">[Pg 19]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_20">[Pg 20]</span> +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.</p> + +<p>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.</p> + +<p>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<span class="pagenum" id="Page_21">[Pg 21]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_22">[Pg 22]</span> +Analysis. Let me cite one example. A slide +prepared and coloured so as to represent +the continuous solar spectrum, marked with +the principal <i>Frauenhofer</i> lines, is placed, say, +in the lower lantern. We now wish to show +the bright lines given by an incandescent +metal, say <i>sodium</i>. 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.</p> + + +<hr class="full x-ebookmaker-drop"> + +<div class="chapter"> +<h2 class="nobreak" id="c4">MAKING OXYGEN GAS.</h2> +</div> + + +<p>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<span class="pagenum" id="Page_23">[Pg 23]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_24">[Pg 24]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_25">[Pg 25]</span> +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.</p> + +<div class="figcenter"> +<img src="images/fig3.jpg" alt="diagram"> +<p class="caption"><span class="smcap">Fig. 2.</span></p> +<p class="caption">Diagram showing relative positions of <i>g b</i>, Gas-bag; <i>w b</i>,<br> +Wash-bottle; and <i>r</i>, Retort.</p> +</div> + +<p>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<span class="pagenum" id="Page_26">[Pg 26]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_27">[Pg 27]</span> +of taking the tube from it, the tap must be +turned. The next thing is to detach the retort +from the purifier <i>before the gas is extinguished +in the stove</i>. 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.</p> + +<p>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<span class="pagenum" id="Page_28">[Pg 28]</span> +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.</p> + +<p>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.</p> + +<p>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.</p> + +<p><span class="pagenum" id="Page_29">[Pg 29]</span></p> + +<div class="figcenter"> +<img src="images/fig4.jpg" alt="iron"> +<p class="caption"><span class="smcap">Fig. 3.</span></p> +<p class="caption">Iron bottle for compressed oxygen gas.</p> +</div> + +<p>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<span class="pagenum" id="Page_30">[Pg 30]</span> +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<span class="pagenum" id="Page_31">[Pg 31]</span> +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.</p> + +<div class="figcenter"> +<img src="images/fig5.jpg" alt="gas-bag"> +<p class="caption"><span class="smcap">Fig. 4.</span></p> +<p class="caption">Gas-bag and pressure-boards.</p> +</div> + +<p>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<span class="pagenum" id="Page_32">[Pg 32]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_33">[Pg 33]</span> +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.</p> + + +<hr class="full x-ebookmaker-drop"> + +<div class="chapter"> +<h2 class="nobreak" id="c5">THE SCREEN OR SHEET.</h2> +</div> + + +<p>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<span class="pagenum" id="Page_34">[Pg 34]</span> +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.</p> + +<p>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-<i>cloth</i> 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.</p> + +<p>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.<span class="pagenum" id="Page_35">[Pg 35]</span> +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.</p> + +<p>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.</p> + +<div class="figcenter"> +<img src="images/fig6.jpg" alt="sheet"> +<p class="caption"><span class="smcap">Fig. 5.</span></p> +<p class="caption">Showing method of hanging a sheet.</p> +</div> + +<p>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<span class="pagenum" id="Page_36">[Pg 36]</span> +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<span class="pagenum" id="Page_37">[Pg 37]</span> +can be carried out by fastening the screw-eye +to a timber upright on each side, supported +by light struts.</p> + +<p>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.</p> + + +<hr class="full x-ebookmaker-drop"> + +<div class="chapter"> +<h2 class="nobreak" id="c6">PICTURES FOR THE LANTERN.</h2> +</div> + + +<p>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<span class="pagenum" id="Page_38">[Pg 38]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_39">[Pg 39]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_40">[Pg 40]</span> +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.’</p> + +<p><span class="pagenum" id="Page_41">[Pg 41]</span></p> + +<p>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.</p> + +<p>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<span class="pagenum" id="Page_42">[Pg 42]</span> +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.</p> + +<div class="figcenter"> +<img src="images/fig7.jpg" alt="easel"> +<p class="caption"><span class="smcap">Fig. 6.</span></p> +<p class="caption">Glass easel.</p> +</div> + + +<p>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<span class="pagenum" id="Page_43">[Pg 43]</span> +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.</p> + +<div class="figcenter"> +<img src="images/fig8.jpg" alt="slides"> +<p class="caption"><span class="smcap">Fig. 7.</span></p> +<p class="caption">Masks for lantern slides.</p> +</div> + + +<hr class="full x-ebookmaker-drop"> + +<div class="chapter"> +<h2 class="nobreak" id="c7">ON THE COLOURING OF PHOTOGRAPHIC<br> +TRANSPARENCIES.</h2> +</div> + + +<p>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<span class="pagenum" id="Page_44">[Pg 44]</span> +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.</p> + +<p>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.</p> + +<p>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,<span class="pagenum" id="Page_45">[Pg 45]</span> +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.</p> + +<p>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:</p> + +<table> + +<tr> + <td class="tdl">Italian Pink.</td> + <td class="tdl">Prussian Blue.</td> + <td class="tdl">Rose Madder.</td></tr> + +<tr> + <td class="tdl">Raw Sienna.</td> + <td class="tdl">Indigo.</td> + <td class="tdl">Purple Madder.</td></tr> + +<tr> + <td class="tdl">Yellow Lake.</td> + <td class="tdl">Neutral Tint.</td> + <td class="tdl">Crimson Lake.</td></tr> + +<tr> + <td class="tdl">Chinese Orange.  </td> + <td class="tdl">McGilp.</td> + <td class="tdl">Burnt Sienna.</td></tr> + +<tr> + <td class="tdl">Brown Pink.</td> + <td class="tdl">Brown Madder.  </td> + <td class="tdl">Ivory Black.</td></tr> + + + +</table> + + +<p>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.</p> + +<p>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.</p> + +<p>A flat porcelain palette is better than one of<span class="pagenum" id="Page_46">[Pg 46]</span> +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.</p> + +<p>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.</p> + +<p>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<span class="pagenum" id="Page_47">[Pg 47]</span> +indefinitely by judicious blending +one with the other. Let me give a few instances.</p> + +<p>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<span class="pagenum" id="Page_48">[Pg 48]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_49">[Pg 49]</span> +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.</p> + +<p>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,<span class="pagenum" id="Page_50">[Pg 50]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_51">[Pg 51]</span> +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.</p> + +<p>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.</p> + +<p>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<span class="pagenum" id="Page_52">[Pg 52]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_53">[Pg 53]</span> +of this nature, the aforesaid ‘Manual +of Water-Colours’ must be studied.</p> + +<p>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.</p> + +<p>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<span class="pagenum" id="Page_54">[Pg 54]</span> +expressed opinion, that oil-colours are the +more suitable pigments to use.</p> + +<p>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.</p> + +<p>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<span class="pagenum" id="Page_55">[Pg 55]</span> +flat woolly head like a mop, which makes an +excellent dabber.</p> + +<p>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.</p> + +<p>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.</p> +<hr class="full x-ebookmaker-drop"> + +<div class="chapter"> +<p><span class="pagenum" id="Page_56">[Pg 56]</span></p> + +<h2 class="nobreak" id="c8">SHOWING SOLID & OPAQUE OBJECTS<br> +ON THE LANTERN SCREEN.</h2> +</div> + + +<p>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 <i>cartes de visite</i>, 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.</p> + +<div class="figcenter"> +<img src="images/fig9.jpg" alt="lantern"> +<p class="caption"><span class="smcap">Fig. 8.</span> Ground-plan of Chadburn’s Opaque Lantern.</p> +<p class="caption"><i>p</i>, Picture; <i>c</i>, Condenser; <i>l</i>, Light; <i>r</i>, Reflector;<br> +<i>o</i>, Objective.</p> +</div> + +<p>The first instrument which was constructed +to accomplish this end is known as Chadburn’s +lantern; and, as will be seen from the +<span class="pagenum" id="Page_57">[Pg 57]</span>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.<span class="pagenum" id="Page_58">[Pg 58]</span> +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.</p> + +<p>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.</p> + +<p>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<span class="pagenum" id="Page_59">[Pg 59]</span> +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.</p> + +<p>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:</p> + +<p>‘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<span class="pagenum" id="Page_60">[Pg 60]</span> +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<span class="pagenum" id="Page_61">[Pg 61]</span> +expert, with the help of a microscope, would +answer the same end.</p> + +<p>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.</p> + + +<hr class="full x-ebookmaker-drop"> + +<div class="chapter"> +<h2 class="nobreak" id="c9">THE LANTERN MICROSCOPE.</h2> +</div> + + +<p>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<span class="pagenum" id="Page_62">[Pg 62]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_63">[Pg 63]</span> +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.</p> + +<p>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.</p> + +<p>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.</p> + +<p>Such a lecture might usefully commence<span class="pagenum" id="Page_64">[Pg 64]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_65">[Pg 65]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_66">[Pg 66]</span> +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.</p> + + +<hr class="full x-ebookmaker-drop"> + +<div class="chapter"> +<h2 class="nobreak" id="c10">MECHANICAL OR MOVING-PICTURES.</h2> +</div> + + +<p>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.</p> + +<p>In another class of slide a circular glass is<span class="pagenum" id="Page_67">[Pg 67]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_68">[Pg 68]</span> +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.</p> + +<p>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.</p> + +<p>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<span class="pagenum" id="Page_69">[Pg 69]</span> +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.’</p> + +<div class="figcenter"> +<img src="images/fig10.jpg" alt="dancing"> +<p class="caption"><span class="smcap">Fig. 9.</span></p> +<p class="caption">Facsimile of a dancing skeleton for Beale’s Choreutoscope.</p> +</div> + +<hr class="full x-ebookmaker-drop"> + +<div class="chapter"> +<p><span class="pagenum" id="Page_70">[Pg 70]</span></p> + +<h2 class="nobreak" id="c11">CONCLUDING REMARKS.</h2> +</div> + + +<p>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<span class="pagenum" id="Page_71">[Pg 71]</span> +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 <i>err</i> 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.</p> + +<p>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,<span class="pagenum" id="Page_72">[Pg 72]</span> +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<span class="pagenum" id="Page_73">[Pg 73]</span> +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.</p> + +<p>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<span class="pagenum" id="Page_74">[Pg 74]</span> +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.</p> + +<p>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.</p> + +<p>The success of a lantern entertainment depends +nearly as much on the competence of<span class="pagenum" id="Page_75">[Pg 75]</span> +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.</p> + + +<p class="c p2">THE END.</p> + +<hr class="r65"> + +<p class="c med sp">BILLING AND SONS, PRINTERS, GUILDFORD. +</p> + +<div class="transnote"> + +<p class="c">Transcriber’s Notes:</p> + +<p>New original cover art included with this eBook is granted to the public domain.</p> + +<p>Variations in spelling and hyphenation are retained.</p> + +<p>Perceived typographical errors have been changed.</p> + +</div> +<div style='text-align:center'>*** END OF THE PROJECT GUTENBERG EBOOK 75890 ***</div> +</body> +</html> + diff --git a/75890-h/images/cover.jpg b/75890-h/images/cover.jpg Binary files differnew file mode 100644 index 0000000..b7d75ea --- /dev/null +++ b/75890-h/images/cover.jpg diff --git a/75890-h/images/fig1.jpg b/75890-h/images/fig1.jpg Binary files differnew file mode 100644 index 0000000..7d05d7a --- /dev/null +++ b/75890-h/images/fig1.jpg diff --git a/75890-h/images/fig10.jpg b/75890-h/images/fig10.jpg Binary files differnew file mode 100644 index 0000000..5c5ece4 --- /dev/null +++ b/75890-h/images/fig10.jpg diff --git a/75890-h/images/fig2.jpg b/75890-h/images/fig2.jpg Binary files differnew file mode 100644 index 0000000..1916dbe --- /dev/null +++ b/75890-h/images/fig2.jpg diff --git a/75890-h/images/fig3.jpg b/75890-h/images/fig3.jpg Binary files differnew file mode 100644 index 0000000..99bec6f --- /dev/null +++ b/75890-h/images/fig3.jpg diff --git a/75890-h/images/fig4.jpg b/75890-h/images/fig4.jpg Binary files differnew file mode 100644 index 0000000..c2e8896 --- /dev/null +++ b/75890-h/images/fig4.jpg diff --git a/75890-h/images/fig5.jpg b/75890-h/images/fig5.jpg Binary files differnew file mode 100644 index 0000000..c0f8eac --- /dev/null +++ b/75890-h/images/fig5.jpg diff --git a/75890-h/images/fig6.jpg b/75890-h/images/fig6.jpg Binary files differnew file mode 100644 index 0000000..9d21654 --- /dev/null +++ b/75890-h/images/fig6.jpg diff --git a/75890-h/images/fig7.jpg b/75890-h/images/fig7.jpg Binary files differnew file mode 100644 index 0000000..56d86dc --- /dev/null +++ b/75890-h/images/fig7.jpg diff --git a/75890-h/images/fig8.jpg b/75890-h/images/fig8.jpg Binary files differnew file mode 100644 index 0000000..da807ef --- /dev/null +++ b/75890-h/images/fig8.jpg diff --git a/75890-h/images/fig9.jpg b/75890-h/images/fig9.jpg Binary files differnew file mode 100644 index 0000000..48b5d0d --- /dev/null +++ b/75890-h/images/fig9.jpg |
