1879.] 



The Chloride of Silver Battery. 



287 



of cooling. It is evident, therefore, that the increase of pressure 

 cannot be ascribed to the instantaneous heating of the bell-jar 82° C. 



Taking the dimensions of the arc from a photograph, it was calcu- 

 lated that it must have attained the enormous temperature of 16,114° C, 

 if the increase of pressure was really due to heat. It was found that 

 platinum wires O'OOl inch in diameter supported in various jmrts f 

 the arc were immediately fused ; the temperature of the arc was there- 

 fore as high as the fusion-point of platinum, and possibly considerably 

 higher. 



If the whole of the heat evolved by a current of 0'01102 W, through 

 a resistance of 600,000 ohms had been communicated to the air in the 

 jar, weighing 0*339 grm. it would raise it 215°'6 C. in one second. 

 It is known from direct experiment that this enormous evolution of 

 heat was not communicated to any extent to the air in the bell-jar, 

 because its temperature only increased about o- 64 C. per second; 

 the heat must consequently have escaped almost instantaneously by 

 radiation. It is difficult consequently to realise the conjecture that 

 the enormous dilatation which occurred instantaneously could have 

 been caused by increase of temperature. And it points to its being 

 produced by a projection of the molecules by electrification causing- 

 them to press outwards against the walls of the containing vessel, this 

 pressure being distinct from the motion caused by heat. 



The authors proceed to describe the appearance of the arc with ter- 

 minals of various forms at different distances and with various pres- 

 sures. It was found that the light emitted by different parts of the 

 arc was not of the same intensity throughout, and that from the first 

 there was a tendency to break up into distinct entities, as shown in the 



Fig. 2. 



ABC D E F 



A fa (\ (h fa fa 



