which gives excellent results in the installation under consideration.
The sixteen lamps are on the divisible system, and their regulation is
based upon the principle of derivation. They are supplied by a Siemens
alternating current machine and arranged in four circuits, on each of
which are mounted four lamps in series. The accompanying figures will
allow the reader to readily understand the system, which is as simple
as it is ingenious, and which has been combined by Mr. Mondos so as to
obtain a continuous and independent regulation of each lamp.

In this system the lower carbon is stationary, the luminous point
descending in measure as the carbons wear away through combustion. The
upper carbon descends by its own weight, and imperceptibly, so as to
keep the arc at its normal length.

The mechanism that controls the motions of the upper rod that supports
the carbon-holder consists of two bobbins of fine wire, E (Fig. 2),
mounted on a derived circuit on the terminals of the lamp; of a lever,
L, articulated at O, and supporting a tube, TT', and the whole movable
part balanced by a counterpoise, P. This lever, P, carries two soft iron
cores, F, which enter the bobbins, E, and become magnetized under the
influence of the current that passes through them. The upper part of
the tube, T, carries a square upon which is articulated at O' a second
lever, L', balanced by a second counterpoise, P', and carrying a flat
armature, _p_, opposite the cores, F', that are fixed to the first
horizontal lever, L. The carbon-holder rod, CC', slides freely in the
tube, TT', and is wedged therein by a small piece, _a m l_, fixed to
the lever, L'. For this reason the tube, TT', is provided with a notch
opposite the piece _a m l_, and the two arms, _a_ and _m_, of the latter
are shaped like a V, as may be seen in part in the plan in Fig. 2. It is
now easy to understand how the system operates; when the current is not