" The reproduction of the phenomena by the aid of a series of successive proofs presented no difficulty. M. Mach was not dealing simply with a single movement resolved into several figures, but with a succes sion of complex movements recorded in a great number of images; there fore, he was led to construct a special instrument which would admit of the examination of a considerable number of proofs without interruption. His apparatus consists essentially of a metal lic drum mounted on a screw-axis, similar to a registering cylinder. For the reception of the positive proofs the stroboscopic drum is pierced with oval openings 15 mm. high and 13 mm. wide. These openings are closed by the photo copies drawn upon thin pellicles of celluloid, and placed in their chrono logical order. The result is that, when the cylinder is set in revolution, all the images are presented successively at the same point in space, which ren ders possible their rapid succession before the eye of the observer, either directly or by projection on a luminous screen.
" In this apparatus of M. Mach, the revolution of the drum is not continuous but intermittent: each image arrives rapidly within the luminous cone of the sciopticon, where it remains immovable for the fraction of a second, then continues its course, disappearing as suddenly as it arrived. The fixity of the object during the short period of observation is necessary to obtain a perfect reproduction of the movements. To realize this succession of advancing movements alternating with short pauses, M. Mach employs an ingenious arrangement which we have not space to describe in detail, but which may be understood by the aid of the illus tration (Fig. ic 2 7).
" By the aid of this apparatus one is able to throw, approximately, ninety five proofs upon the screen in the course of fifteen seconds.
" The spectator witnesses a very curious scene: he sees the plant grow before his eyes and is able to follow all its transformations. Apart from the phenomenon of growth proper, one observes, too, the phenomenon of heliotropism, that is, the turning of the leaves toward the light—the move ment of the leaves, etc.
" The development, at first very rapid, is progressively retarded, a period of great activity succeeding one of relative repose. At this moment, the flowers appear. We see them ex pand and wither. The plant itself is subject to the same laws. We see the cotyledons rise from the seed, to be followed by leaf, flower, and fruit, and lo ! the plant withers before our eyes, the whole process of birth, growth, flowering, fruiting, and decay, occupy ing a space that may be counted by seconds." • CHRYSOTYPE.—One of Sir John Herschell's processes. A sheet of paper was immersed in a moderately strong solution of ammonio-citrate of iron andWried in the dark. The paper is then exposed to the light under the negative until a very faint impression is obtained. The development took place by brushing over the exposed paper a neutral solution of gold of such strength as to appear the color of sherry. The print then turns to a purple tint, and is washed in several changes of water, and fixed in a weak solution of iodide of potassium, washed again, and dried.