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. [Illustration: Fig 130.—The Praxinoscope Theatre.] [Illustration: 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 The stem and handle are then withdrawn, and as the top will continue to spin for a long time, discs and various outline shapes can be fixed upon it, and various objects will be shadowed thereon.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. FOOTNOTES: [12] From _praxis_, action, and _skopein_, to show. CHAPTER XII. OPTICAL ILLUSIONS CONTINUED—EXPERIMENTS—THE TALKING HEAD—GHOST ILLUSIONS. The enumeration of optical illusions is so considerable that we have no intention of describing them all, and will merely cite a few other examples. The following facts have been communicated to us by M. Nachet:— [Illustration: Fig. 132.—Hexagonal appearance formed by circles joined together.]