nt electrometer (Fig. 4), in
which the horizontal 8-shaped needle is replaced by two connected
cylindrical surfaces that move in a cylinder formed of four parts; a
Von Beetz commutator; spyglasses with scale for reading measuring
instruments (Fig. 3); apparatus for the study of magnetic variations,
of Lamont (Fig. 3) and of Wild (Fig. 5); different types of the
Wiedemann galvanometer; an electrometer for atmospheric observations
(Fig. 6); a dropping apparatus (Fig. 7), in which the iron ball opens
one current at a time at the moment it leaves the electro-magnet and
when it reaches the foot of the support, these two breakages producing
two induction sparks that exactly limit the length to be taken in
order to measure the time upon the tracing of the chronoscope
tuning-fork; an absolute galvanometer; a bifilar galvanometer (Fig. 8)
for absolute measurements, in which the helix is carried by two
vertical steel wires stretched from o to u, and which is rendered
complete by a mirror for the reading, and a second and fixed helix, so
that an electro-dynamometer may be made of it; and, finally, a
galvanometer for strong currents, having a horseshoe magnet pivoted
upon a vertically divided column which is traversed by the current,
and a plug that may be arranged at different heights between the two
parts of the column so as to render the apparatus more sensitive (Fig.
9).

[Illustration: FIG. 2.--ZENGER'S UNIVERSAL ELECTROMETER.]

We may likewise cite the exhibit of Mr. Eugene Hartmann of Wurtzburg,
which comprised a series of apparatus of the same class as those that
we have just enumerated--spyglasses for the reading of apparatus,
galvanometers, magnetometers, etc.

[Illustration: FIG. 3.--EXHIBIT OF TH. EDELMANN.]

Specially worthy of remark were the apparatus of Mr. Kohlrausch for
measuring resistances by means of induction currents, and a whole
series of accessory instruments.

Among the objects shown by other exhibitors must be mentioned Prof.
Von Waltenhofen's differential electromagnetic balance. In this, two
iron cylinders are suspended from the extremities of a balance. One of
them is of solid iron, and the other is of thin sheet iron and of
larger diameter and is balanced by an additional weight. Both of them
enter, up to their center, two solenoids. If a strong current be
passed into these latter, the solid cylinder will be attracted; but
if, on the contrary, the current be weak, the hollow cylinder will be
at