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 SEISMOGRAPH.]

_Scateni's Registering Seismograph._--This apparatus, which is shown in
Figs. 7 and 8, consists of two parts--of a transmitter and of a
registering device.