k-case. Both
communicate with the extremities of the circuit in which is interposed the
seismic telltale that brings about a closing of the current. Having noted
the position of the hands on the dial when the clock was running, one can
deduce therefrom the moment at which the shock occurred that set the clock
in motion.

In addition to the parts that we have described, there are other accessory
ones, R R_r_, and a third clamp, 3, which constitute a sort of rheotome
that is designed to keep the circuit closed after the momentary closing
that is produced by the telltale has occurred. This little mechanism is
indispensable when the disturbed telltale has also to act upon an electric
bell. This rheotome, which is very simple, is constructed as follows: A
small brass rod, R, which is screwed to the support, S, carries at its
left extremity a brass axis, X, which is insulated from the rod, R, by
means of an ivory piece. Toward the center of this small rod, the bent
lever, _r_, carries a small arm that is bent forward, and against which
abuts the axis of the pendulum, thus causing it to be thrust toward the
left when the pendulum is arrested by the projection of the finger, A. As
soon as the pendulum is set free, the lever, _r_, redescends and places
itself against the axis, X. This latter communicates with clamp 3, which
is insulated, while the rod, R, communicates with clamp 1. The external
communications are so arranged that the circuit in which the bell is
interposed remains definitely closed when the lever, _r_, is in contact
with the rod, X.

[Illustration: FIG. 6.--ROSSI'S TREMITOSCOPE.]

_Rossi's Tremitoscope._--This instrument (Fig. 6) unites, upon the same
stone base, three different arrangements for showing evidences of
trepidations of the earth. On one side we find (protected by a glass tube)
a weight suspended over a mercury cup by a spring, and designed to show
vertical motions. The two other parts of the apparatus are designed for
registering horizontal motions. The first is a pendulum which causes a
contact with four distinct springs, and whose movements are watched with a
spy-glass. The second is a steel spring which carries at its upper part a
heavy ball that vibrates at the least shock. This ball is provided with a
point which is movable within a second ball, so that its motion produces
a contact. All these different contacts are signaled or registered
electrically.

[Illustration: FIG. 7.--SCATENI'S SEI