334 



and appearance (figs. 2 or 3), the discharge from the nitric-acid 

 battery quickly alters : as the action of the battery improves, the glow 

 round the negative terminal enlarges, heat in that portion of the tube 

 is sensibly developed, as can be ascertained by touching the tube with 

 the hand, and in a few seconds the negative ball becomes red-hot. 

 During this time no apparent sign of chemical action takes place in 

 the cells of the battery ; the heating effect appears to be mainly due 

 to the elevation of tension ; for if the copper wires attached to the ter- 

 minals rest on gold-leaf electroscopes, the leaves continue expanded 

 until the arc discharge takes place, when they instantly collapse, and 

 heat is evolved at the positive terminal. 



17. In vacuo, as long as the intermittent discharge continues, resist- 

 ance apparently takes place at the negative terminal ; and this is not 

 only evinced by the heat which is evolved, but by the disruption of 

 the metal which is separated from this pole in minute particles, and 

 deposited in a lateral direction on the sides of the vacuum-tube. 



IS. As soon as the action of the battery becomes sufficiently 

 energetic, so as to cause the continuous or arc discharge to pass, an 

 entirely new effect is developed : the discharge itself becomes intensely 

 vivid, the stratifications assume a conical form with their apex di- 

 rected towards the negative (fig. 5), and heat is instantly perceptible 

 at the positive terminal, while the negative as instantly cools. 



19. It is beautiful and interesting to observe the suddenness with 

 which the red heat of the negative terminal ball disappears, and the 

 equal suddenness with which the heat is at the same instant elicited 

 in the positive, when the brilliant arc discharge takes place. 



From the results obtained by these experiments, I infer that the 

 development of heat, either at the positive or the negative pole of a 

 voltaic battery, is entirely due to the amount of resistance which 

 takes place in that part of the battery circuit. 



