CHAP, vii i.l THE ELECTRIC LIGHT. 



A~C v pT 

 ' 



CHAPTER VIII. 



THE ELECTRIC LIGHT. 



I. REGULATORS OF ELECTRIC LAMPS. 



R the light of the sun the most dazzling light that can be 

 produced artificially is the electric light. This is obtained by 

 the incandescence of two carbon poles completing the circuit of a 

 powerful battery or of a magneto-electric machine. Attempts have 

 been made to utilise this light for a great number of industrial, 

 military, and scientific purposes, as also for the lighting of streets 

 and squares, for works which must be continued through the night, 

 for submarine constructions, works in the galleries of mines, military 

 and marine reconnoitring by night, lighthouses, and for particular 

 effects of decoration in theatrical representations. In most of these 

 various applications success has crowned the endeavours that have 

 been made, but not without calling for special researches and the 

 overcoming of special difficulties. 



One of the chief of these difficulties consisted in the discontinuity 

 of the light caused by the separation of the poles due to the combustion 

 of the carbon. It is known, in fact, that when the light is produced, the 

 current carries over from one cone to the other excessively fine portions 

 of matter one of the carbons appears to elongate at the expense of 

 the other ; but in reality, as combustion is in question, the distance 

 between the two points goes on increasing ; in proportion as they are 

 blunted the current grows weaker, the intensity of the light decreases, 

 and at the end of a certain time ceases altogether. In the case in 

 which the current employed is that of a galvanic battery, and is therefore 

 always in the same direction, the wearing away of the cones of carbon 

 is in the ratio of one to two ; the positive pole being used the quickest. 



x x 



