According to the inventor, this lamp will give a light of 100 carcels per one horse-power, and with a three horse-power six lamps may be lighted; but we have made no experiments to ascertain the correctness of these figures.
As for the cost of the glass rods, that amounts to one franc per two hundred meters length. They can, then, be considered only as an insignificant expense in the cost of the carbons. We consequently believe that it will be possible to employ this system advantageously in practice.--_Th. du Moncel_.
Since the month of May last, the concert at the Champs Elysées has been lighted by sixteen voltaic arc lamps on a new and very simple system, 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 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.