1 7 2 ELECTRIC LIGHTING. 



wheels by the movement of the box. The lamp is thus 

 lighted; but in proportion to the consumption of the carbons, 

 the resistance of the light circuit increases, and the current, 

 passing with more intensity into the derivation, soon becomes 

 sufficiently powerful to release the clockwork that brings the 

 carbons together, until the current has regained its full inten- 

 sity in the light circuit. Things go on in this way until the 

 carbons are entirely consumed. 



It will easily be understood that with this arrangement 

 there is no limit to the length of the carbons, since it may 

 exceed that of the apparatus, and without their requiring any 

 particular position. Their forward movement takes place 

 as if they glided between the fingers of two hands, pushed 

 towards each other by two thumbs guiding their progress. 



This lamp, like those of Serrin and Siemens, may be 

 lighted from a distance, which is not one of the least of its 

 advantages. A medal was awarded to it at the Exposition 

 Universelle of 1878. 



Biirgiu's Lamp. This lamp is already rather old. and 

 we are surprised that it has not been described anywhere, 

 for, according to what Soret has communicated to me, it 

 works in the most satisfactory manner. It was shown at 

 the Exposition of 1878, but, its inventor being absent when 

 the jury went round, it was not examined. It is used con- 

 tinuously at Geneva for the theatre and for the illumination 

 of a public clock. 



Biirgin has made two patterns of this lamp, one of which 

 is for industrial purposes, and is represented in Fig. 43 ; the 

 other, more complicated, is intended for scientific experi- 

 ments. The principle of the lamp is very simple : the two 

 carbon-holders tend to approach each other continuously by 

 the influence of a spring barrel or a counterpoise; but they 

 can obey this tendency only when a check controlled by an 

 electro-magnetic action permits the passage of the chain or 

 chains which support the carbon-holders, so that, according 



