VOL TAIC ARC LAMPS. 1 r 



requisite to make the regulator suitable for these two sources of 

 electricity. When the arc that springs between the carbons is 

 derived from, the battery, they are consumed in the ratio of i to 

 2 ; if, on the other hand, it is derived from the magneto-electric 

 machine, the consumption of both carbons is alike, since the 

 currents are alternating. In the former case it is necessary to 

 arrange the advance of the carbons in the ratio of I to 2, and in 

 the latter to make it equal. An addition to the mechanism 

 enables the change of the relative velocities of the carbons to be 

 made in an instant, according as one or the other source of elec- 

 tricity is made use of. 



" Thus improved, the new regulator is perfectly adapted to all 

 the applications of the electric light." 



Serrin's Lamp. Of all the regulators yet invented, that 

 of Serrin is the one most used when a prolonged illumination 

 is required. We have had the pleasure of following the 

 various phases through which this apparatus has passed since 

 its invention, and we were the first to give a complete account 

 of it in tome IV. of the second edition of our Expose des 

 applications de Felectritite, published in 1859. At a later 

 period, Pouillet, in a report made to the Academic des Sciences, 

 explained its ingenious arrangements. Finally, the experi- 

 ments made with the machines of the Alliance Company 

 showed that it was then the only apparatus that could work 

 with currents alternately reversed. Since that period this re- 

 gulator has been constantly used in the various experimenls 

 that have been made with the electric light, and it is the one 

 adopted in the illumination of lighthouses. We must there- 

 fore dwell a little on this ingenious apparatus, which is so 

 sensitive that an india-rubber ring placed between the two 

 carbons is sufficient to arrest their progress without the ring 

 losing its shape. 



This apparatus, which is able, like that of Duboscq, to 

 keep the luminous point stationary, is essentially formed ol 

 two mechanisms mutually connected, but each producing its 

 own effect on the movement of the carbons. One of these 



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