﻿178 Mr. J. C. Pomeroy on the Charges on Thermions 



set o£ readings of less than 1° C; but when, after the 

 readings for Q r /Q c had reached a maximum and become 

 steady, the temperature of the whole apparatus was raised 

 about 4° C, there was no appreciable change in Q r /Q c . So 

 the idea that the variation in Q r /Q c might be due to a change 

 of temperature of the air in the chamber " K " was finally 

 disposed of. The result seems to confirm the conclusion 

 reached above — that the changes in Q,./Q c were not due to 

 unsteady air-currents — for the outside heat was applied 

 entirely from one side and would be much more likely to 

 cause an uneven distribution of heat, and hence unsteady 

 air-currents, than would the heated strip which was placed 

 centrally above the testing-chamber. 



IV. During the early experiments the strips of thin 

 platinum were soldered directly to heavy copper connecting 

 wires, but this was found to be unsatisfactory, as even when 

 care w T as taken to use as little solder as possible, it fused with 

 the platinum on being heated, and sometimes only three or 

 four readings could be obtained from one strip. Then, 

 doubtless, ionization was obtained from the solder as well as 

 from the platinum. To avoid this the thin platinum was 

 welded to thicker pieces of the same metal and the latter 

 attached to the leads by small screw clips. 



Jt is worth noting that the larger values of Q r /Q c corre- 

 sponded roughly to the initial positive ionization and to the 

 increased ionization at high temperatures. At first sight it 

 might appear that the increased number of ions might have 

 something to do with the change in Q r /Q c , but if this had any 

 effect it would be due to the mutual repulsions between the 

 ions, and this would be greater, and hence the spreading of 

 the stream greater, when the ionization w 7 as strongest, but the 

 opposite was the case, the number reaching the outer ring- 

 being greatest when the ionization was least. Then, too, 

 no such effect was noticed when the ionization from RaBr 

 was used, though the ionization was much greater than that 

 from the hot platinum. Thus the conclusion that there was 

 an actual change in the charges seemed inevitable, and efforts 

 were made to get at the reason for this variation. 



At first, when positive ions were being tested, the platinum 

 was heated to a temperature only sufficiently high to produce 

 these, but not high enough to give negative ions, and the 

 temperature w r as increased only when it was desired to obtain 

 the latter. Under these conditions it w^as found that the 

 positive ions from a fresh strip carried an average charge 

 nearly double that obtained with radium. While the strip 



