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