2 1 2 ELECTRIC LIGHTING. 



it by the conductor /' and the interrupter M v. In order to 

 avoid the poisonous vapours emitted by the mercury in con- 

 sequence of becoming heated, the cap B is insulated from 

 the tube T by means of a substance not a conductor of heat, 

 and it communicates with the base of the lamp through the 

 copper conductor /, which, being a good conductor of heat, 

 diffuses it and withdraws it from the mercury. 



This system, by its simplicity, permits the lamp to be very 

 cheaply made. It had. however, been already devised by 

 Reynier, who had pointed it out amongst the arrangements 

 that might be given to his apparatus. 



Tommasi's Lamp. In order to obtain a longer duration 

 of the working of the preceding lamps, Tommasi arranged 

 them like a revolver. For this purpose, the lamp is formed 

 of an iron tube about 3 centimetres in diameter, turning on 

 a pivot and supporting five carbons of 30 centimetres length, 

 and these, one after another, are by a rotatory movement 

 brought into contact with the carbon disc of the negative 

 pole, and thus the light is produced for eight or ten hours. 

 The forward movement of these carbons is effected by mer- 

 cury contained in the tube, as in the preceding system, and, 

 according to Moigno, the light thus supplied is very uniform 

 and steady. This lamp has the shape and size of an ordi- 

 nary Carcel lamp. 



Edison's Lamp. The reputation that Edison acquired 

 by the invention of the phonograph was the cause of con- 

 siderable financial disasters, when some time ago he an- 

 nounced that he had finally found the long-sought solution 

 of the problem of the division of the electric light. He was 

 taken at his word, and in America, as well as in England and 

 in France, the shares of the gas companies fell enormously. 

 It was forgotten that the American newspapers were often 

 the propagators of false news; and since the phonograph 

 triumphantly refuted the denials with which its announce- 



