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.
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 This pioneer form of opaque lantern has been superseded by the instrument called the Aphengescope.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.