It now remains to say a few words about Prof. Von Beetz's chronograph. This instrument (Fig. 17) is designed for determining the duration of combustion of different powders, the velocity of projectiles, etc. The registering drum, T, is revolved by hand through a winch, L, and the time is inscribed thereon by an electric tuning fork, S, set in motion by the large electro-magnet, E F. Each undulation of the curves corresponds to a hundredth of a second. The tuning-fork and the registering electro-magnets, G and H, are placed upon a regulatable support, C, by means of which they may be given any position desired.
FIG. 11.—VON BEETZ'S SOLENOID FOR DEMONSTRATING THE CONSTITUTION OF MAGNETS.
The style, c, of the magnet, C, traces a point every second in order to facilitate the reading. The style, b, of the electro-magnet, H, registers the beginning and end of the phenomena that are being studied.
FIG. 12.—APPARATUS FOR DEMONSTRATING THE PRINCIPLE OF THE GRAMME MACHINE.
The apparatus is arranged in such a way that indications may thus be obtained upon the drum by means of induction sparks jumping between the style and the surface of the cylinder. To the left of the figure is seen the apparatus constructed by Lieutenant Ziegler for experimenting on the duration of combustion of bomb fuses.
Shortly after the drum has commenced revolving, the contact, K, opens a current which supports the heavy armature, P, of an electro-magnet, M. This weight, P, falls upon the rod, d, and inflames the fuse, Z, at that very instant. At this precise moment the electro-magnet, H, inscribes a point, and renews it only when the cartridge at the extremity of the fuse explodes.
