INCANDESCENT LAMPS. 205 



" A rod of carbon T rests gently by its weight and that of 

 its carrier on the periphery of a roller of retort carbon N, 

 and the imperfect contact thus produced gives rise to the 

 incandescence and combustion of the stick of carbon at its 

 extremity." 



We may remark, however, that with this arrangement, in 

 which the transmission of the cur- 

 rent to the movable carbon is not 

 produced by a sliding contact, placed 

 at a short distance from the point, 

 that the light is only produced at 

 the point of contact, and it can be 

 but very feeble, whilst with Reynier's 

 system, in which this sliding contact 

 exists, the portion of the carbon be 

 tvveen it and the roller is heated to 

 incandescence. It appears also, on FIG. 55. 



an attentive examination of the pa- 

 tent, that the carbon roller N was made of alternately in- 

 sulating and conducting portions ; and as it was subjected 

 to a rapid rotatory movement, the light was the result of a 

 series of sparks which were produced at the moment of the 

 passage of the carbon T on each of the insulating portions. 



Werdermann's Lamp. Werdermann's lamp is in prin- 

 ciple merely Reynier's lamp reversed ; but this arrangement 

 is more practical for public illumination, for which it was 

 specially intended, and it makes use of the voltaic arc 

 action. It is represented in Fig. 56. 



This system consists essentially of a slender carbon b 

 moving within a metallic tube T, which serves at once as 

 guide and conductor of the current A collar fixed on the 

 lower part connects it by means of two cords which leave 

 the tubes by two grooves and pass over two pulleys to a 

 counterpoise P that tends constantly to raise the carbon, and 

 to keep it lightly pressed against a large carbon disc c of 2 



