traversing the circuit, the carbons are separated; but, at the moment
the circuit is closed for lighting a series of lamps, it traverses the
electro-magnet, which then becomes very powerful, and draws down the
cores, F, along with the lever, L, the tube, TT', and the carbon-holder,
CC', and brings the carbons in contact. The arc then forms, and the
current divides between the arc and the bobbins, E. Its action upon the
cores, F, becomes weak, and it can no longer balance the counterpoise,
P, which falls back, and raises the system again. The arc thus
becomes _primed_. The cores, F, however, preserve a certain amount of
magnetization; the armature, _p_, is attracted, and the lever, L',
assumes a position of equilibrium such that the piece, _a m l_, wedges
the rod, CC', in the tube, TT', and holds it suspended. When, through
wear of the carbons, the arc elongates, a greater portion of the current
passes into the bobbins, E, the armature, _p_, is attracted with more
force, and the lever, L', swings around the point, O'. The rotation of
L' separates the piece, _a m l_, from the rod, CC', which, being thus
set free, slides by its own weight and shortens the arc. The current
then becomes weak in E, the armature, _p_, is not so strongly attracted,
the lever, L', pivots slightly around O' under the action of the weight,
P', and the brake or wedge enters the notch anew, and stops the descent
of the carbon. In practice, the motions that we have just described are
exceedingly slight; the carbon moves imperceptibly, and the length of
the arc remains invariable.

[Illustration: Fig. 1--MONDOS'S ELECTRIC LAMP.]

It will be seen, then, that the lever, L, and the tube, TT', serve
exclusively for _lighting_, and the lever, L', exclusively for
regulating the distance of the carbons.