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machine, and L L the lamps. In this case the current requires to have a high electro-motive force in order to overcome the added resistance of the whole number of lamps. Such a current is supplied by the Brush generator or the peculiar form of Gramme generator employed by Jablochkoff. These are the currents which are dangerous to life and limb unless they are properly insulated; and it is by these that one or two fatal accidents have occurred through negligence. The other way of arranging the lamps is to connect them singly or in little groups by cross wires between two main conductors joined to the brushes of the generator м, as shown at L L in Fig. 73. Then the current, instead

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of traversing one lamp after another, splits up between the lamps, part going through one lamp or group, and part through another. The resistance of any particular path or channel for the current is in such a case not very great, and the electro-motive force of the current need not be dangerously high. It is on this plan that incandescent lamps are generally arranged for domestic purposes, and the current flowing in the wires about a house would of course be harmless. These lamps can be mounted on an ordinary chandelier.

The aim of electric lighting companies is to found central stations in different districts of a town, and there manufacture electricity, which would be distributed to all the houses in the district, just as gas is

now. In order to carry this out properly, a means of storing the electric power is necessary, in order that there should be a stock in hand for use by day, when the generators were not working, or in case of accident. In the so-called "secondary batteries," or accumulators, of M. Faure, MM. Sellon and Volckmar, and others, we have a means of doing so. The Faure accumulator, Fig. 74, consists of two lead plates, overlaid with red-lead and sheathed in felt, then rolled up together and plunged in a vessel containing acidulated water. When these two plates are connected by their terminal wires (+), to the poles of a generator, electric energy can be pumped into the cell, so to speak, and there magazined. On disconnecting the generator and joining the plates of the cell through a wire or through electric lamps, as the case may be, an electric current is found to flow out of the cell in the reverse direction to that which flowed in from the generator. The Sellon-Volckmar accumulator is similar to Faure's, but the plates are simply placed side by side in the acidulated water, and the red-lead is filled in the form of paste into round holes cast in the metal plates.

The Sellon-Volckmar cell is made in the form of a wooden case containing the liquid and the plates. These plates are an alloy of lead, and the paste is filled into the perforations. The absence of the coating of red-lead and the cloth sheathing, reduces the internal resistance of this battery and makes it restore some 80 or 90 per cent. of the current put into it. Binding-screws are fitted on the cover to connect up the wires which run to the lamps.

At the Electric Exhibition in the Crystal Palace during the summer of 1882, the Lane-Fox incandescent

lamps in the Alhambra Courts were lit by the current from these accumulators; and the intensity of the light was easily graduated by switching in or out a group of cells. The current from them is quite steady,

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and the lamps are found to stand a higher current and give a brighter light than they could if fed by the current from a dynamo direct. This is owing to the fact that the currents from even the best dynamos are vibratory and shake the filaments.

Some 70 or 80 per cent. of the energy of the current from the generator can thus be reclaimed at any future time. No doubt this is a considerable loss, but when we remember that the variable power of winds, waves, and waterfalls—which is now largely wasted-could in this way be utilised, the practical gain is seen to be considerable. Moreover, these accumulators are certain to be improved in course of time, and there is no doubt but they would be very useful at central stations or in houses for yielding a supply of current which would serve for household uses whilst the generators were idle. They also serve to regulate the electric light, as they render the currents from the generator more continuous, and less liable to break the carbon filaments in an incandescent lamp.

Indeed, it is not unlikely that these accumulators will be specially used for rendering the intermittent current absolutely continuous. The arrangement is shown in Fig. 75, where D is the dynamo generating the current, which is led away to the accumulators A A A by conducting wires w w. The lamp circuits L L, instead of being connected in the direct circuit of the wires w w, are joined across the poles of the accumulators, and draw a steady current from it, all the while the dynamo continues to charge them with more or less intermittent currents. Should the dynamo stop working from any cause, the lamps will not go out, because of the charge remaining in the accumulators.

Secondary batteries charged with electricity could of course be delivered to consumers like other goods, and returned empty to be charged again; but this

way of distributing the current does not seem a profitable one, and will only be resorted to in special cases, where a temporary supply is wanted. A surgeon or an electrician may sometimes require a portable charge for medical or for testing purposes, which an accumulator

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will enable him to have. In the actual cautery a fine platinum wire heated to incandescence is now employed to sever the flesh, and in examinations of the mouth and other parts of the body difficult of access, a tiny electric light is sometimes used. Such is the polyscope of M. Trouvé, which comprises a case containing either

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