[Illustration: FIG. 5.--BRASSART'S SEISMIC CLOCK.]
_Brassart's Seismic Clock._--This apparatus is designed for being put in connection at a distance with an indicator like the ones just described. It is a simple clock to which a few special devices have been added. Seismic clocks may be classed in two categories, according as they are stopped by the effect of a shock or are set running at the very instant one occurs. The Messrs. Brassart have always given preference to those of the second category, because there is no need of watching them during a seismic calm, and because they are much more easily constructed. It is to this class, then, that their seismic clock belongs. It is capable of being used for domestic purposes in place of any other clock, and of becoming a seismoscopic clock as soon as it is put in electric communication with the seismic telltales.
To the cross-piece that holds the axle of the drums the inventors have added (Fig. 5) a support formed of a strip of brass, S, with whose extremity is jointed (at the lower part) a double lever, A. This latter is held in a horizontal position by a small counterpoise, _i_, so that the finger at the opposite extremity shall prevent the pendulum, P, from swinging. To keep the latter in a position of rest a bent lever, _n n'_, is jointed to the upper part of the support, S. The longer arm, _n'_, of this lever is bent forward at right angles, so that it may come into contact with and repel the small rod of the pendulum as soon as the lever has been lifted by means of a small cord which is connected with the larger arm, _n_, and runs up to a small hook, from whence it descends and makes its exit under the clock-case.
In order to stop the clock, then, it is only necessary to pull on this cord slightly, when, by moving the pendulum to the left, it will thrust it against the inclined plane of the finger of the lever arm, A. It is clear that the extremity of the pendulum, upon striking against the finger, will depress it slightly and go beyond the projection against which it remains fixed owing to the counterpoise, _i_. The fever, _n n'_, is brought back to its position of rest by means of a small counterpoise at the extremity of the arm, _n_. When the lever, A, is depressed, the pendulum escapes and sets the clock running. This depression is effected by means of an electro-magnet, E, whose armature, which is connected with the rod, _t, t_, lifts the arm, _i_, of the lever, and depresses A. The wires of the two bobbins of the electro-magnet end in two clamps, 1 and 2. The second of these latter is insulated from the clock-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.