Dissolving views, as the name implies, is an exhibition of pictures in which there is a fading away of one and the appearance of another, as though the one picture grew out of the wreck of the other. To produce these results, two lanterns of similar size are required (see [Fig. 4]), together with some contrivance for diminishing the light forming the first picture, until that has quite faded away, simultaneously allowing that forming the second picture to fall upon the screen until this one has arrived at its complete intensity, and the first picture is no longer seen. This latter contrivance is known as the mechanical dissolver, and it consists of two serrated plates attached to a movable bar fixed to the front edge of the base upon which the lanterns are supported. These plates come immediately in front of the lanterns, and require to be so arranged that when the whole of the light from one lantern is seen on the screen, the light from the other is entirely stopped. By means of a rack and pinion motion, the plates can be moved simultaneously, and each lantern alternately closed and opened.
In order to make the discs of light produced by the two lanterns coincident, the lanterns must be slightly inclined towards each other.
There is another class of results obtained by the dissolving-views apparatus, which may be designated as the production of ‘composite’ pictures or ‘effects,’ as, for instance, a soldier is seen asleep by the watch-fire, he dreams, and the subjects of his dream appear, one after the other, on the screen, and then fade away. A ship is seen at sea; day turns into night; the moon rises; a violent storm comes on; the lightning flashes, and the ship is set on fire. A water-mill is shown with the stream running and the wheel revolving; a swan appears on the water and moves across the stream; night comes on, the wheel ceases to revolve, and the windows of the house are lit up; clouds flit across the sky; the moon rises—day returns, but the scene has changed to winter; the water is frozen, and its surface occupied by skaters, and a fall of snow takes place.
To produce such effects as these, both lanterns are required to be open at the same time, and the serrated plates forming the dissolver must be so contrived that the one which would otherwise obscure the fixed picture is turned aside, or removed altogether, and therefore only one lantern is alternately opened and closed. The foundation picture (the sleeping soldier, for example) is placed in the lantern that remains constantly open, and to this the addition (the dream) are made with the second lantern.
For dissolving views proper, only two lanterns are required, and for the simpler form of effects two lanterns suffice; but for very complex pictures, three, four, or even five lanterns are required. Any two lanterns of equal size and power may be employed to produce dissolving views; but the phantasmagoria lantern is the smallest that can be advantageously used.
6.—THE LIME-LIGHT.
We have described the typical oil-lit lanterns, and now we shall explain the production of the lime-light in its two principal modifications of the ‘oxycalcium’ and the ‘oxyhydrogen’ light. The lime-light is obtained by intensely heating a piece of lime, in which condition it emits a most brilliant light. The lime is generally used in the form of a cylinder seven-eighths of an inch diameter and one and a quarter inch long, having a hole along its centre from end to end; these cylinders are sold in tin boxes, each containing twelve.
When a box containing lime cylinders has been opened, it is best to transfer the cylinders to a wide-mouth stoppered bottle, and keep the same in a dry place, as moisture causes the lime to crumble to dust. As the lime is only required to furnish some solid material capable of being rendered incandescent, many other substances can be used for this purpose—the best substitute, if lime cannot be obtained, being chalk.
The oxycalcium light requires for its production a large loose flame, a jet of oxygen gas, and a cylinder of lime. The two instruments now to be described—one known as the oxycalcium jet and the other as the oxycalcium lamp—fully realise these conditions, and although accomplishing the purpose in somewhat different ways, each form of instrument possesses some special advantage.
