In Fig. 1, _E_ is a helix of brass wire (gauge about one millimetre); the helix consists of fourteen or fifteen turns, and has a diameter of from twenty to twenty-five millimetres; it hangs from a fine metal spring, and can be raised or lowered by a thumb screw. From the lower end of the helix hangs a copper cone with a platinum point; the latter is kept close to the surface of mercury in the iron basin, _f_, which rests on an insulating column of wood or marble, _G_. The distance of the point from the surface of the mercury remains constant, as the metal pillar, _T_, is of such a length that its expansion or contraction by change of temperature compensates that of the helix; the latter is in connection (by _T_) with one pole of a Daniell's battery of two cells, and the basin, _f_, is connected with the other pole. Any vertical movement, however slight, makes the platinum point dip into the mercury, and thus completes the circuit. In this circuit are included two electro-magnets, _C_ and _D_; these, during the circulation of a current, attract their armatures, which are connected with levers. The action of _C's_ lever is to stop the clock, _A_, which thus records, to a half-second, the time of the occurrence of the shock, at the same instant that the clock strikes an alarm bell, which attracts the attention of an observer. The lever, attached to the armature of _D_, at the first instant of the current frees the pendulum of the clock, _B_, which was before kept from swinging, in a position out of the vertical; the clock then acts as a time-piece, and its motion unrolls a band of paper, _k k k_, at a rate of three metres an hour. At the same time the armature of _D_, while attracted, presses a pencil point against the band of paper which passes over the roller, _m_, marking on it, while the earthquake lasts, a series of points or strokes which occupy a length of paper corresponding to its duration, and which record the work of the shock. After it is over the paper continues to unroll from the drum, _i_, and passing round the clock, rolls on to the drum, _l_. If a fresh shock occur the pencil indicates it, as before, on the paper, and the length of blank paper between the two sets of marks is a measure of the interval of time between the shocks. By way of additional check, several helices, _h h h_, are hung from a stand, with small permanent magnets suspended from their ends; below and close to these latter are small basins, holding iron filings; into these the points of the magnets dip, when their helices oscillate vertically, and some filings remain sticking to the magnets as a record of the shock. One of the magnets has a shoulder on it which moves an index hand along a graduated arc, as shown in Fig. 2, thus again registering the amount of the vertical movement. Such are the arrangements intended for the record of the undulatory or horizontal elements of the wave of shock.