VOLTAIC ARC LAMPS. 



167 



weight, the carbons are soon sufficiently apart to produce a 

 voltaic arc of suit- 

 able size, which 

 increases in length 

 in consequence of 

 the consumption 

 of the carbons ; 

 but when their dis- 

 tance apart be- 

 comes too great, 

 the intensity of the 

 current becoming 

 too weak is unable 

 to cause the at- 

 traction necessary 

 for the action on 

 the wheel i, and 

 then the wheels 

 can turn freely, 

 causing thereby the 

 approach of the 

 carbons, which 

 goes on until the 

 current has re- 

 gained an inten 

 sity sufficient to 

 again produce the 

 effects we have 

 already studied. 

 By a suitable ad- 

 justment of the 

 screws R, K, and 

 z, the double in- FlG - 4*. 



verse action we have just examined may be made very re- 

 gular. But this adjustment is very delicate, and that is 

 perhaps an inconvenience of the system. 



