Fig. 128.—M. Reynaud’s Praxinoscope.
Fig. 129.
Besides the attractions offered by the animated scenes of the Praxinoscope, the apparatus may also be made the object of useful applications in the study of optics. It permits an object, a drawing, or a colour, to be substituted instantaneously in experiments on secondary or subjective images, etc., on the contrast of colours or the persistence of impressions, etc. We can also make what is called a synthesis of movements by placing before the prism a series of diagrams of natural objects by means of photography.
M. Reynaud has already arranged an apparatus which exhibits in the largest dimensions the animated reflection of the Praxinoscope, and which lends itself to the demonstration of curious effects before a numerous auditory. The ingenious inventor has recently contrived also a very curious improvement in the original apparatus. In the Praxinoscope Theatre he has succeeded in producing truly ornamental tableaux, as on a small Lilliputian stage, in the centre of which the principal object moves with startling effect. To obtain this result, M. Reynaud commences by cutting out in black paper the different figures, the whole of which will form an object animated by the rotation given to the Praxinoscope. To supply the decorations, he arranges on the black foundation the image of an appropriate coloured design by means of a piece of glass. It is well known that transparent glass possesses the property of giving a reflection of the objects on the nearest side as well as on the farthest. We may recall the applications of this optical effect in theatres, and also in courses of physics, under the title of impalpable spectres. It is also by reflection on thin, transparent glass, that M. Reynaud produces the image of the ornamentations in the Praxinoscope Theatre. The decorations are really placed in the lid, which is held by a hook in a vertical position, thus forming the front side of the apparatus (fig. 130). In this side a rectangular opening is made, through which the spectator (using both eyes) perceives at the same time the animated reflection of the Praxinoscope, and the immovable image of the decorations reflected in the transparent glass. The position of the latter and its distance from the coloured decorations are arranged so that the reflection is thrown behind the moving figure, which consequently appears in strong relief against the background, the effect produced being very striking. It is evident that to change the decorations it is only necessary to place in succession on a slide the different chromos representing landscapes, buildings, the interior of a circus, etc. It is easy to choose an arrangement suitable for each of the moving figures placed in the Praxinoscope. By this clever and entirely novel optical combination, the mechanism of the contrivance is entirely lost sight of, leaving only the effect produced by the animated figures, which fulfil their different movements on the little stage. The Praxinoscope Theatre can also be used as well in the evening as in the daytime. By daylight, it is sufficient to place it before a window, and in the evening the same effects may be produced, perhaps in even a more striking manner, by simply placing a lamp on the stand, with a small plated reflector, and a lamp-shade. The illusion produced by this scientific plaything is very complete and curious, and M. Reynaud cannot be too much commended for so cleverly applying his knowledge of physics in the construction of an apparatus which is at the same time both an optical instrument and a charming source of amusement.
Fig 130.—The Praxinoscope Theatre.
Fig. 131.—The Dazzling Top.
Amongst the toys founded upon the persistency of impressions upon the retina we may instance the “Dazzling Top” (fig. 131). This remarkable invention is quite worthy of a place in every cabinet, and is an ingenious specimen of a perfected Helmholtz top. It is a metallic toy put in motion by means of a cord wound round a groove. The axis is hollow, admits a metallic stem, and fits into a handle which is held in the hand. The top is placed upon a little cup in an upright position, and it is then set spinning in the usual way with the cord. The stem and handle are then withdrawn, and as the top will continue to spin for a long time, discs and various outline shapes can be fixed upon it, and various objects will be shadowed thereon. Cups, bowls, candlesticks, and jugs can be seen plainly revolving as the top carries the wire representation in outline rapidly past the eyes. Coloured cardboard can be worked into various patterns, and much amusement will be created amongst children and young people.