298 



Scientific Proceedings^ Royal Dublin Society. 



place. The negative numbers were very small compared with the positive 

 the rate of flow of the air being slow (1200 ecs. per min.). The saturation 

 current was ten times as great for positive as for negative numbers. The 

 positive ions were saturated between 320 and 400 volts, giving a mobility 

 between '0015 and ■0012. The negative ions had a lower saturation point, 

 and were thus smaller than the positive. The numbers obtained are shown 

 in the following table : — 



Currents oltained on heating glass ttibe and eliarging nuclei hy 

 ultra-violet light. 



On the other hand, as might be expected, it was proved in many experi- 

 ments that when nuclei are driven from a glass tube by heat and passed over 

 uranium, the resulting numbers, positive and negative, are equal, any 

 charged products from the glass tube being previously removed to earth, as 

 in our other experiments. 



It was thought possible that passing dry air through the glass tube would 

 remove the matter which gives rise to the condensation nuclei driven off by 

 heat. A glass tube, however, through which dry air had passed for several 

 hours was unchanged, and gave the same effect as before the drying. Whether 

 the air drawn through the glass tube while heated is dry or moist makes no 

 difference in the numbers of nuclei emitted. 



In dealing witli soft glass tubes a second- type of nuclei emission was 

 encountered with stronger heating. If a soft glass tube be heated with a 

 luminous flame, the emission falls off almost to zero in ten or fifteen minutes. 

 If the fatigued part be now heated with a strong Bunsen flame, the emission 

 is very much increased, and remains constant for a long time, no sign of 

 fatigue being observed. In this second case the glass tube glows, and the 

 ni(clei are due probably to the decomposition of the glass itself, 



