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machine, B. This latter machine generates short positive and negative currents alternately, some 16,000 of them per minute. These currents are led by wires, E E, to the "commutator," c, and from the commutator by other wires, E' E', to the lamp D. In each lamp there are four separate candles, but only one burns at a time. The current passes up one carbon, traverses the kaolin, and down the other; and if the current were always in one direction, the positive carbon, or that connected to the positive pole of the machine, would be wasted away much faster than the other; but by the device of alternating the currents the carbons are alternately worn away at an equal rate. Each candle only burns one hour and a half, but the commutator serves automatically to turn the current into the next candle. the instant that the last has burned sufficiently low. In this way the four candles burn six hours. The dynamo-electric machines, A and B, are of course turned by a belt from any shafting driven by steam or other motive-power, such as water-wheels or gas-engines. By a particular arrangement of the interior of the machine, eight, ten, or even sixteen separate lights may be fed from one machine, but the usual number is six.

The electric candles of Wilde, Rapieff, Jamin, and others, are modifications of Jablochkoff's, in which the clay separator of the carbons is replaced by air. In Jamin's candle the current is also caused to circulate round about the two carbon sticks in an oval ring of wires in order that the attraction between that portion of the current flowing in the upper part of the ring and the arc, which may be considered as a mobile element of the current, shall draw the light upwards, and thus

lengthen the arc into a kind of flame. M. Jamin has also constructed a candle which, like that described, is fed by alternating currents; but in it the two carbons come together and separate at each rapid alternation of the current, thereby giving a variable arc, which, however, appears to the eye of constant length.

The "Lamp Soleil," or sun lamp, is allied to the Jablochkoff candle, but differs from it in construction.

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As shown in Figs. 65 and 66, it consists of two carbon rods c c stuck through a block of marble or limestone B, contained in an iron case A A open at the bottom. A slip of carbon D connects the two ends of the rods and serves as a priming to start the current, which is brought by wires to the two carbons. When the current is once started this priming disappears, the marble between the ends of the rods becomes white

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hot, and a mellow beam of light resembling sunlight is shed down from the lamp as shown in Fig. 66. The sun lamp is very simple and inexpensive, and yields a rich light suitable for picture galleries and shops.

Very powerful arc lights are now produced for light-houses and for exploring fortifications or searching for torpedo boats in time of war. Lights of from 10,000 to 150,000 candles are employed, and great reflectors, such as the Holophote of Siemens, and the Projector of Col. Mangin, are placed behind the arc to throw the penetrating beam in a particular direction. These arc lights are gradually gaining ground in the lighting of streets and cities. In California the entire town of San José is lighted by a few powerful lamps placed on tall iron masts, fitted with umbrella-like reflectors, which shed the light downwards over a large area. The flickering noticeable in single lamps when near them is absent from the blended radiance of several lamps placed at a distance overhead, and it is probably by imitating the sun and other celestial orbs in this way that extensive out-of-door illumination by the electric light will be effected.

In passing from the more powerful arc lights destined for large areas, to the incandescent lamps intended for indoors, we encounter a class of lamp coming between the "arc" and "incandescent sorts, viz., the semi-incandescent lamp of Reynier and Werdermann.

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FIG. 67.

The light-giver or electro-pyre (to coin a special word) is formed of a pointed pencil of carbon A Fig. 67 abutting on a block of carbon B: and the current flowing between the pencil and block raises the joint to a white heat. The light is mainly emitted by the

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