206 



ELECTRIC LIGHTING. 



indies diameter, which is kept in a fixed position by a ver- 

 tical support D. This support is fixed to a kind of funnel- 

 shaped covering s, which receives the ashes from the com- 

 bustion, and permits a glass globe to be fitted to the lamp. 



The upper carbon disc is connected with the negative pole 

 of the generator, and the metallic guide T of the carbon 

 pencil corresponds with the positive 

 pole, so that only the portion of the 

 carbon between the tube and the 

 upper carbon is brought to incan- 

 descence. This incandescence is in- 

 creased by the action of the small 

 voltaic arc which, as we have said, 

 is formed at the point of contact of 

 the two carbons, and it is increased 

 also by the combustion of the at- 

 tenuated carbon. The upper carbon, 

 by virtue of its greater mass, neither 

 burns nor changes. The action of 

 the counterpoise is regulated by 

 means of a spring K provided with 

 an adjusting screw, which, by press- 

 ing more or less on the part of the 

 tube surrounding' the carbon, acts as 

 a brake. The greater or less pres- 

 sure of this brake depends on the 

 formation of the voltaic arc between 

 the two carbons, or merely on the incandescent effects, 

 and it is in this circumstance that the difference between 

 Werdermann's and Reynier's system specially resides. In the 

 latter the movable carbon is too contracted to take part in 

 the formation of an arc, whilst in the other this carbon is 

 sufficiently free for this effect to be produced ; and thus the 

 diameter of the movable carbon may without inconvenience 

 be increased for the purpose of making it last longer. In 

 the new forms of the Werdermann lamp the upper disc of 



