condensing electrometer, by giving it, according to the distance of
the disks, different degrees of sensitiveness. One constructor who
furnished much to this part of the exhibition was Mr. Th. Edelmann of
Munich, whose apparatus are represented in a group in Fig. 3. Among
them we remark the following: A quadrant 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,