Siemens’ lamp is at the present time employed in the Lizard Lighthouse, in Messrs Siemens’ Engineering Works in England and Wales, as well as in other localities or buildings requiring powerfully lighting up.
An interesting illustration of the value of the electric light to the sailor is furnished by the ‘Telegraph Journal’ of April 5th, 1878. This publication contains a letter from the captain of the S.S. ‘Faraday,’ narrating how that vessel was by its means prevented from running into another vessel during a dense fog.
Siemens’ magneto-electric apparatus and lamp were used on the occasion above referred to.
In every form of contrivance for electrical illumination the lamp or lighting apparatus consists of carbon points separated by a very slight interval, through which the current of electricity passes by means of terminal wires attached to the dynamo-electrical machine.
The lighting effect is produced by the passage of the electric spark through the small gap which separates the carbon points, in which interval extremely minute but solid particles of carbon, given off by the points, are heated up to incandescence in the path of the spark, and thus give rise to the intensely luminous focus known as ‘the electric light.’ The brilliancy of the light of course depends upon the quantity of electricity employed.
A very large number and variety of designs and patents for electric lamps have made their appearance in England, America, France, and Russia within the period following the invention of the small, powerful, and economic dynamo-electric machines of Siemens and Gramme.
The lighting apparatus generally attached to and worked by that variety of Gramme’s machine generating the continuous current is that known as the ‘Serrin Lamp.’ Two carbon electrodes placed vertically one above the other (the positive being the upper one) are fixed on brass holders, which are so connected by a suitably contrived clockwork movement, combined with the working of an electro-magnet in connection with the electric circuit, as to maintain the two carbon poles during their combustion at the necessary distance from each other. Serrin’s lamp differs in detail from Siemens’, but, like this latter, is automatic in principle. In Paris it was the one in general use until the introduction of the Jablochkoff candle, and, with the Duboscq lamp, may be looked upon as the precursor of the various lamps and regulators now employed in electric lighting. Serrin’s lamp or regulator, with some slight modification in the machinery, is also used in the Lontin system of electric illumination, by which separate lights are supplied by separate circuits of electricity. Lontin’s method is that by which the Gaiety Theatre in the Strand is lighted; and is also used at the Western Railway Station (Gare, St Lazare) at Paris. The Jablochkoff candle, which in Paris has lately superseded the Serrin lamp, probably because its use renders unnecessary the use of automatic machinery, is the invention of a Russian engineer, whose name it bears.
It consists of two sticks of gas carbon, about 9 inches long and 1⁄5th of an inch thick, which are placed vertically side by side, and insulated from one another by a very thin strip of kaolin or china clay (a silicate of alumina and potash), the whole forming a candle. Each carbon rod is connected with one of the terminal wires of a Gramme dynamo-electric machine, the electric current from which, however, not being continuous, sets up an
alternate current between the tips or poles of the candles, which are gradually consumed like an ordinary taper, and with this only difference in action between Serrin’s and Siemens’ lamps, that whereas in these latter the spark passes from the top to the bottom carbon point, in the Jablochkoff candle it jumps from side to side. The inventor contends that the kaolin by becoming heated diminishes the resistance of the circuit, and thus permits of the passage of the electric spark more easily through the carbons, and also, we believe, asserts that the kaolin being electrolytically decomposed as the carbons are consumed, becomes converted into silica, which melts and drops down, whilst the aluminium liberated contributes luminosity during combustion to the flame.
One of the chief advantages, however, claimed by M. Jablochkoff is, that he can divide the circuit into a number of different lights, as the resistance of the circuit is uniform.