ond. 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: FIG. 13.--VAN RYSSELBERGHE'S REGISTERING
THERMOMETROGRAPH.]

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.

[Illustration: FIG. 14.--VAN RYSSELBERGHE'S REGISTERING
THERMOMETROGRAPH.]

This apparatus perhaps offers the inconvenience that the drum must be
revolved by hand, and it would certainly be more convenient could it
be put in movement at different velocities by means of a clockwork
movement that would merely have to be thrown into gear at the desired
moment. As it is, however, it presents valuable qualities, and,
although it has already been employed in Germany for some time, it
will be called upon to render still more extensive services.

[Illustration: FIG. 15.--HARLACHER'S APPARATUS FOR STUDYING DEEP
CURRENTS IN RIVERS.]

We have now exhausted the subject of the apparatus of precision that
were comprised in the Munich Exhibition. In general, it may be said
that this class of instruments was very well represented there as
regards numbers, and, on another hand, the manufacturers are to be
congratulated for the care bestowed on their construction.--_La
Lumiere Electrique_.

[Illustration: FIG. 16.--HARLACHER'S APPARATUS FOR STUDYING DEEP
CURRENTS IN RIVERS.]

[Illustration: FIG. 17.--VON B