of the inductor, and is provided at the center with two
helicoidal grooves, e, at right angles with one another. In these grooves
slides a tappet, n, connected with the axle.

[Illustration: FIG. 1.]

Under the influence of the counter-spring at the left of the disk, P, the
latter constantly tends to occupy the position shown in Fig. 2, which is
that of rest. As soon as the winch, K, is revolved, whatever be the
direction of the motion, the axle can only be carried along when the
tappet, n, has come to occupy the position shown in Fig. 3, that is to
say, when the disk has moved from right to left a distance corresponding
to the fraction of the helix formed in the sleeve.

This stated, it is easy to understand the travel of the currents. Fig. 1
shows the station at rest. The current that arrives through L passes
through the lightning protector, the body of the commutator, U, the
terminal, v, and the call, W, bifurcates at P, and is closed by the
earth. The inductor is in circuit, but, as it is in derivation, upon a
very feeble resistance, v, nearly the whole of the current passes through
the latter. When it is the station that is calling, the call, W, is put
in derivation upon the circuit, f_{2} p, h, so that the portion of the
circuit that passes through q W v is exceedingly feeble, and incapable of
operating the bell of the post that is calling.

[Illustration: FIGS. 2 AND 3.]

Finally, when the telephone is unhooked, the inductor, J, and the bell,
W, are thrown out of circuit, and the telephone is interposed between d
and i, that is, between L and T.--_La Lumiere Electrique_.

* * * * *

THE GERARD ELECTRIC LAMP.

In the Gerard incandescent lamp the carbons have the form of a V. They
are obtained by agglomerating very finely powdered carbon, and passing it
through a draw plate. At their extremity they are cemented together with
a small quantity of carbon paste, and their connection with the platinum
conducting wires is effected by means of a cylinder of the same paste
surmounted by a cone. These couplings secure a good contact, and, by
their dimensions, prevent the attachments from becoming hot and
consequently injuring the carbon at this point. The cone forms a
connection of decreasing section, and prevents the carbon from getting
broken during carriage.

This process of manufacture permits of obtaining lamps of all
intensities, from 3 candles up. The following, accor