Part 6

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.’

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.