On the Heat developed at the Poles of a Voltaic Battery. 227 



8. The preceding experiments, so far from assisting me in explain- 

 ing the cause of the heating of the positive pole of the voltaic battery, 

 rather tended to complicate the inquiry ; for experiment now showed 

 that in carbonic acid vacua the heating effect was elicited at the nega- 

 tive pole, whether the discharge was made from a voltaic battery or 

 form an induction coil ; but as experiment also showed that heat is 

 always evolved from the latter at the negative, whether in air or in 

 vacuo, and that from the battery it always in air appears at the posi- 

 tive, it was evident the media through which discharges were made 

 afforded no explanation for the elucidation of a phenomenon of which 

 hitherto the more it was examined by experiment the more difficult 

 appeared the solution. 



9. My next experiments were made in vacuum-tubes in which balls 

 of carbon were inserted in lieu of metal. With these I at first obtained 

 the usual heating of the negative, but in one instance I observed that 

 both balls were at the same time exhibiting red heat ; in this instance, 

 either from some alteration having taken place in the vacuum, or from 

 some other cause which I had not time to examine, the discharge from 

 the carbon balls became so uncertain as to afford me little information 

 worth recording, except as to the fact I have stated of both balls 

 being heated : the cause of this I was subsequently enabled to deter- 

 mine. 



10. In two of the vacuum-tubes hollow brass balls had been at- 

 tached to the platinum wires. In the first of these the negative very 

 soon became heated by the discharge. As the discharge of the battery 

 continued, a sudden flash of light was visible in the vacuum, and the 

 glass instantly became coated with metal. On examining the tube, I 

 ascertained that one-half of the negative ball was separated from the 

 other, and partly fused : the intense heat had vaporized the silver 

 with which the two hemispheres forming the ball had been soldered, 

 and it was this vaporized metal that was deposited on the sides of 

 the tube. The positive ball remained much tarnished, as if it had also 

 been heated. 



11. I then introduced the second tube, having similar hollow 

 brass balls, into the circuit of the battery. In this tube the negative 

 also was at first heated to redness ; when in this state, a sudden bril- 

 liant stratified discharge took place, as fig. 5. 



Fig. 5. 



The evolution of nitrous acid fumes in the battery denoted its in- 

 tense action. This discharge from the battery continued for about two 

 seconds, the negative ball instantly losing its luminosity, the positive 

 becoming red-hot. 



12. This experiment appeared to offer an explanation as to the 

 cause of the heating of the poles ; but on attempting to repeat it, the 

 tube was unfortunately fractured by the heating of the platinum wire, 

 as were also two tubes with coke balls : the result I had obtained was, 



