The Magic Lantern and Its Management

Part 1

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

T. C. HEPWORTH

LATE LECTURER ON SCIENCE TO THE ROYAL POLYTECHNIC INSTITUTION, LONDON.

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.

Part 2

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.

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.

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