In the evening, a lamp placed on a support _ad hoc_, in the centre of the apparatus, suffices to light it up very clearly, and a number of persons may conveniently assemble round it, and witness the effects produced. [Illustration: Fig. 128.—M. Reynaud’s Praxinoscope.] [Illustration: 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.