300 



Scientific Proceedings, Royal Dublin Society. 



voltage curve was plotted for Co, and the mobilities deduced from the saturation 

 voltages. The results are seen in the following table : — 



When 1-5 amperes were used saturation did not occur even at 400 volts, the 

 highest voltage obtainable at the time. The numbers, however, show clearly 

 how the size of the nuclei depends upon the temperature of the wire. 



In observing the emission from platinum at a given temperature, no 

 falling-off is observed even after hours ; but if the same wire is heated from 

 day to day, a gradual falling-off is observed, although as long as the wire is 

 glowing nuclei are always emitted in large numbers. 



In addition to the nuclei given off by platinum when glowing, nuclei are 

 also emitted at lower temperatures by fresh wires, but the effect falls off' 

 rapidly to zero, and is thus not easily detected. A fresh wire was heated by 

 currents from '5 ampere up, and the values of C, and Cj taken at each reading 

 of the current. No nuclei were observed at "5 amp. nor at "8 amp. ; but 

 when the current was I'D amp., C2 was originally four times Ci, but rapidly 

 fell off to a value near d, showing that the emission of nuclei fell off to zero. 

 The wire just began to glow at 1"1 amps., and at that low temperature, 

 although the emission never fell off' to zero, the wire, when fresh, emitted 

 more nuclei than after it had been heated for some time. 



Taking another new piece of wire, the following values of Ci and C2 were 

 got for the given currents through the wire. Gi and C2 are given in arbitrary 

 units : — 



Thus a large number of nuclei were emitted when 0'8 ampere passed 

 through the wire. Three readings, each taking about one minute, were made 



