In the second cylinder is found a magnifying-glass, convex on both sides, the focus whereof is double to that of the half ball, and one third of its diameter: this glass is called “the eye-glass.” It is by means of drawing those glasses close that the objects are magnified; and by removing them at a distance, that the figures are made to look smaller. Inside of the box is placed one of those lamps called “argand,” of a wide diameter, with a concave mirror, to throw as much light as possible upon the transparent figures.
To exhibit the phantasmagoria, select an apartment opening into a second room, and the door of which is at your disposal: take a wooden frame, exactly of the same dimensions as that door, upon which fasten, with brass nails, a sheet of fine linen, in preference to calico. A moment before you place the frame, wet it equally all over, to cause the thread of the cloth to swell, and to fill all interstices.
When you have proved the above-mentioned instrument, prior to your using it, make sure that the lamp does not smoke, but that it gives a vivid light; that the concave mirror is very bright; that the magnifying-glass is dry and clean. (You dry these with a piece of soft leather and some whitening, so fine as not to scratch. The painted glasses are cleaned with a piece of very fine cloth, made quite hot, or of cambric, taking care not to rub off the painting.) You then place the wooden ruler with the reversed figure in the slide, opened purposely to receive it, in the first cylinder; then, the figures being reflected on a whitewashed wall, you regulate the distance of the magnifying-glasses, in order to have the paintings seen in all their perfection at a regular fixed distance. Your instrument is then ready for the exhibition.
To this effect, you present yourself facing the framed linen, with the phantascope suspended before you, and held by two braces across your shoulders. In order that the figures may decrease in the eyes of the spectators of the other side, you must advance slowly near the cloth, drawing the two magnifying-glasses at a distance from each other, but very gently, that the figures should remain steady.
If, on the contrary, you should wish them to appear magnified, gradually draw back, with the same precaution, and bring the glasses nearer each other; when they are quite close, the figures seem to be coming towards the spectators, and to proceed forward.
When you change the paintings, you must hide the eye-glass behind an opaque and black body. The knowledge of the management of the glasses, and the accuracy of the proceeding backward and forward, upon which depends entirely the good effect of the exhibition, may be acquired by a few days’ practice previous to the exhibition being made in company.
Notwithstanding the box for the phantascope, if made of wood, will be heavier than a tin one, yet it is to be preferred, on account of its communicating much less heat than the tin.
Such persons as wish to paint their figures should use a varnish that does not spread on the glass; thick copal varnish will answer the purpose.
The Enchanted Mirrors.
Make a box of wood, of a cubical figure, of about fifteen inches every way. Let it be fixed on a pedestal, at the usual height of a man’s head. In each side of this box, let there be an opening of an oval form, ten inches high, and seven wide.