in a direction opposite thereto, and into one of the corrugations, where it rests, so that the direction of the shock is indicated.  But, in falling, it causes the lever, F, to tilt, and this brings about an electric contact between the screw, h, and the column, n, which sends a current into the electro, E, so that the armature of the latter is attracted.  In its position of rest this armature holds a series of parts, S, A, L, which have the effect of stopping the pendulum of a clock placed upon the same apparatus.  At the moment, then, that the armature is attracted the pendulum is set free and the clockwork is started.  As the current, at the same time, sets a bell ringing, the observer comes and arranges the apparatus again to await a new shock.  Knowing the hour at which the hand of the clock was stopped, he sees how long it has been in motion again and deduces therefrom the precise moment of the shock.

The small rod, f, which is seen at the extremity of F, is for the purpose of allowing electricity to be dispensed with, if need be.  In this case the screw, h, is so regulated that F descends farther, and that f may depress the armature of the magnet just as the current would have done.

[Illustration:  FIG. 4.—­APPARATUS FOR THE STUDY OF VERTICAL MOVEMENTS.]

Apparatus for the Study of Vertical Movements.—­In this apparatus (Fig. 4), the contact is formed between a mercury cup, T, and a weight, D. The cup is capable of being raised and lowered by means of a screw, so that the two parts approach each other very closely without touching.  At the moment of a vertical shock a contact occurs between the mercury and weight, and there results a current which, acting upon the electro, E, frees the pendulum of the clock as in the preceding apparatus.  In this case, in order that the contact may be continuous and that the bell may be rung, the piece, A, upon falling, sets up a permanent contact with the part, a (Fig. 3).

[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.