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.
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