The electropyre consists of four carbons a a' b b'. opposed to each other in pairs, forming a figure × with this difference, that the lower pair is set in a plane at a right angle to the plane of the upper pair. Sometimes the upper pair is replaced by a single carbon of double thickness. Between the points of the carbons c is formed the luminous arc, as in ordinary arc lamps. It is regulated by the weight w and cords n, e. Electric regulator lamps are now so numerous that a special treatise would be necessary to describe them all. We have selected the most typical samples for illustration, but there are scores of others equally deserving of note, such as the clockwork lamp of Mr. R. E. Crompton, the clutch lamp of Mr. Hawkes, the lamps of Weston, Gravier, Solignac, and Gülcher.

The last two are notable for the ingenuity of their regulation in the Solignac a little glass arrester is melted when one of the carbons burns too near it, and the regulator thereupon adjusts the carbons afresh ; in the Gülcher the upper carbon holder is an iron rod, which can drop by its own weight past the pole of an electric magnet in circuit with the arc; and whenever the arc becomes too wide and the current weakens in the electro-magnet the restraining attraction of the magnet, which has hitherto held the rod from dropping, is enfeebled and the carbon holder slides down, bringing the upper carbon nearer to the arc. When, however, this operation is completed and the current regains its normal strength, the magnet re-asserts its hold on the rod and arrests its descent, until a further adjustment is necessary.

The Jablochkoff electric candle is now chiefly notable because it gave a great impulse to electric lighting in

A

1878, when it was introduced into the streets of Paris. The candle consists of the usual pair of carbon points, but instead of being pointed to each other they are placed side by side and separated from each other by a strip or plate of kaolin or plaster of Paris, thus Fig 63, where a and B are the carbons and c the kaolin. The candle stands upright in a socket or candle stick, and the current being sent up the stick A crosses the top of the kaolin c and flows down the stick B. To start the light the current first passes through a strip of conducting composition c between the two carbons across the edge of the kaolin. Between A and B is the luminous arc or candle flame, a brilliant centre emitting a delightfully soft and fairly steady light. It owes its soft diffusive quality to the kaolin, which is heated to whiteness at the tip and melts away like wax at the same rate as the carbons are consumed; but it is occasionally vitiated by a violet tinge due to impurities in the plaster of Paris.

A

FIG. 63.

B

B

The peculiar advantage of Jablochkoff's system lies in the constant and continuous circuit provided for the current across the luminous clay. The variableness of the voltaic arc is thus to a great extent avoided without requiring any regulating mechanism.

The electric generator of the current employed by M. Jablochkoff is a Gramme or dynamo-electric machine, which gives rapid alternations of positive and negative currents. Fig. 64 shows the arrangements

required for lighting Jablochkoff's electric candle by this machine. A is a small Gramme machine of the ordinary kind, which supplies the current necessary to magnetise the electro-magnets of the alternating

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.

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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