331 



assumes the form represented in fig. 2. This discharge, as well as those 

 from the induction coil and the water-battery, when examined, is found 

 to be very perceptibly intermittent, and will generally continue for some 

 time after the circuit has been completed. As the action of the bat- 

 tery improves, the luminous glow round the negative metallic ball 

 gradually increases in size, and in a few seconds the ball becomes 

 red-hot. This result I repeatedly obtained ; and in two instances 

 with tubes in which balls of aluminium, \ inch diameter, had been 

 inserted, the negative dropped from the wire into the tube in a molten 

 state, but leaving the positive ball with its original metallic lustre. 



Fig. 4. 



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 



2 B 2 



