Fig. 293.
The magic lantern.
In many books full directions are given for painting the glass slides, but this is an art that requires very great practice and experience. A person may know how to draw and paint on paper or canvas, but it is quite a different thing where glass is concerned, and unless the juvenile artist has taken lessons from a regular painter on glass, his or her efforts are likely to be very unsatisfactory. In many popular works embracing the subject of optics, full directions are given on the mode of painting the slides for the magic lantern, or dissolving views; a new era, however, has dawned upon this mode of illustration, in the preparation of photographs on glass of the most lovely description, and now instead of exhibiting mere daubs of weak colouring, photographic pictures of singular perfection can be procured of Messrs. Negretti and Zambra, Holborn, who have turned their attention especially to this branch, and supply slides of all sizes.
II. The Dissolving Views.
This very pleasing modification of the ordinary magic lantern is displayed with the assistance of two lanterns of the same size, provided with lamps and lenses which are exactly alike. They are best arranged on one board, side by side, and if kept parallel with each other, the circles of light thrown from the two lanterns would not coincide on the screen; it is therefore necessary to place one of them at an angle which will vary according to the distance from the screen. The task of making the two circles of light overlap each other precisely on the disc, is called centering the lanterns, and is the first thing that must be attended to before exhibiting the slides. The slides for the dissolving views are all painted of the same size, and supposing a scene such as a church with a bridal procession and the trees in full foliage, to represent summer, is first thrown on to the disc, it may be changed to winter by putting another picture of the same subject, but painted to represent bare trees, and the church and ground covered with snow, and a grave open, with a funeral procession. The two pictures must not be projected on the screen at the same time, and here the dissolving mechanism is required; it consists of two fans so arranged that they may be raised or lowered by a rack-work and handle; one fan in descending covers one of the nozzles of the lanterns, and the other leaves the second lantern open, and free to project the picture; the dissolving is managed by slowly moving the handle of the rack-work, so that one quarter of the picture already on the disc is cut off, and one quarter of the new one thrown on. As the movement proceeds, one half of the old picture is shut out, and one half of the new slide takes its place, and so on, till the whole of the original picture is cut off by the fan and the new one comes into view, and it is in this way the effect of the change from summer to winter is produced. (Fig. 294.)
Fig. 294.
Nozzle of one lantern, with the fan, a, raised, and in the position to throw a picture on the disc. b. The other fan shutting off the second lantern.
When two pictures such as those already described, dissolve one into the other, of course the same building or other marked portion of the subject, must strictly coincide in each picture on the disc, or else the two pictures are apparent, and the illusion is destroyed. The pictures must all be centered before the exhibition commences. By the arrangement of Mons. Duboscq, one electric light serves to illuminate both lanterns by making use of mirrors. The dissolving apparatus is likewise very simple, and consists of two diamond-shaped openings in a brass frame, which open and shut alternately by a slide worked with a handle. The single light is not to be recommended, as it is somewhat troublesome to manage properly. (Fig. 295.)