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Dissolving Views

These can only be exhibited with either two lanterns or with that form of lantern with two lights and two sets of lenses known as the biunnial. The lime light is almost invariably used for the production of dissolving views, but as it involves expensive apparatus and the use of two gases, oxygen and hydrogen, it is hardly suitable for junior hands. The two gases, when combined, constitute an explosive vapour which is highly dangerous in the hands of those unaccustomed to their use, and many lamentable accidents have been the result of tampering with them. So I advise my young readers to be content with the lesser light given by paraffine. In the lime light, the two gases are contained in separate bags, which are weighted in order to force them through india-rubber pipes leading to the lantern. Here they mix and are projected upon a cylinder of lime, which is thus brought to a white heat. The dissolving effect is caused by the gradual extinction of the light in one lens, while it is as gradually produced in the other. As each lens is furnished with a different picture, the two images coalesce upon the screen until one altogether disappears, and the other takes its place. The effect is managed by a "dissolving tap," which shuts the gases off one lens as it opens a way for them to the other lens. The same effect can also be produced by the action of moving screens in front of the lanterns, but by the former plan much gas is saved.