574 Mr. A. Wood on Spontaneous Ionization of 



time, and so would draw fresh air into the vessel. The 

 decrease in the leak which sometimes followed — e.g. after 

 the second heating in the above experiment — is no doubt to 

 be attributed to the diminished density of the air at the 

 higher temperature. It now became necessary to ascertain 

 whether this increase was due to an emanation or merely to 

 free ions. For this purpose a brass tube was inserted between 

 the glass tube containing the granulated tin and the measuring- 

 vessel down the centre of which passed a wire which was kept 

 charged to a potential of 280 volts. The outside of the tube 

 was kept to earth, and as the tube was about 65 cms. long it 

 must have been practically impossible for free ions to make 

 their way along it to the vessel. With this change in the 

 apparatus, heating the tin produced no effect on the ionization 

 in the vessel. The following are the details of two experi- 

 ments carried out with samples of the same tin, the 

 experimental arrangements being identical in the two cases, 

 except that in the first experiment there was no field applied 

 to the brass tube, while in the second a field of 280 volts was 

 applied. 



Time. Potentiometer Readings. Ionization. 



10.40 760 0-863 



10.51 790 0-884 



11.2| 760 0-863 



11.13| 750 0-857 



Glass tube heated 11.24£ to 11.28. 



11.24* 1200 1-092 



11.35} 750 0-857 



11.47* 750 0-857 



11.58* 750 0-857 



12.10" 720 0-837 



12.21| 740 0-850 



Glass tube heated 12.32* to 12.35*. 



12.32| 800 0-889 



12.44" 750 0-857 



The glass tube was now emptied and refilled with some 



fresh tin and the experiment repeated, this time with the 

 field on. 



Time. Potentiometer Headings. Ionization. 



9.27 700 0-823 



9.38 750 0-857 



9.50* 790 0-884 



10.1* 750 0-857 

 Glass tube heated 10.13* to 10.16*. 



10-12* 620 0-765 



10-24 7G0 0-863 



10-35 725 0-840 

 Glass tube re-heated 10.46 to 10.49. 



10.46 770 0-870 



