APPARATUS FOR THE ELECTRIC LIGHT. 14? 



him this plan gave very good results, and with an electro- 

 plating Gramme machine arranged for quantity he was able 

 to light in 10 derived circuits 10 lamps of this kind, each 

 giving a light equal to 40 candles.* The experiment he 

 made on this occasion on the influence exerted by electrodes 

 of carbons of different diameters, being very interesting as 

 regards the present question, we here give them from a paper 

 presented to the Academic des Sciences on the i8th November, 

 1878: 



" When the electric arc is produced between two carbons of 

 the same section," says Werdermann, " the changes in the polar 

 extremities take place thus : the positive electrode heated to 

 whiteness takes the shape of a mushroom, is hollowed into a crater 

 form, and is consumed twice as fast as the negative electrode. 

 The latter, which is only heated to redness by the current, is then 

 slowly shaped into a point, and the length of the arc is in pro- 

 portion to the tension of the current. 



" Things do not pass thus if a different section is given to each 

 electrode. When the section of the positive electrode is gradually 

 lessened, and that of the negative electrode increased, the red 

 heat seen at the point of the latter diminishes more and more, 

 whilst the heat of the positive electrode increases in proportion 

 to the reduction of the section. The electric current no longer 

 passes over the space between the electrodes with the same 

 facility, and in order to maintain the voltaic arc the electrodes 

 must be brought nearer together. 



" A strange phenomenon then appears ; the end of the positive 

 electrode enlarges considerably, and the current shows a ten- 

 dency to equalize the two surfaces, that is to say, to give to the 

 positive electrode as much as possible the same section as the 

 negative. The greater the difference between the sections of the 

 carbon, the more must the distance between them be lessened ; 

 and to avoid too great a swelling of the positive electrode the 

 tension of the current must be a little reduced, which is easily 

 done by using a Gramme machine, with which the tension of the 



* According to Werdermann, the machine required only 2 horse-power to 

 yield this light. But I am informed that this is incorrect, and that a much 

 greater force must be taken into account. 



IO 2 



