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LI. The Effect of Change of Temperature on Spontaneous 

 Ionization. By Normax Campbell, Fellow of Trinity 

 College y Cambridge *. 



1. "FN a recent paper t I described some curious changes 

 JL in the spontaneous ionization o£ a vessel which is 

 being either heated or cooled. Since the changes appeared 

 to have no connexion with the problem of the radioactivity 

 of ordinary materials, which was at that time under con- 

 sideration, further investigation of them was postponed. At 

 intervals during the last two and a half years a large number 

 of additional observations have been made : the effects can 

 now be described with some completeness, and a tentative 

 explanation of them offered. The changes observed are of 

 great complexity and seem to be of little intrinsic interest, 

 but, since other workers may be troubled by them, it is 

 desirable to record the following notes. 



Experimental Arrangements. 



2. The dimensions of the tin vessel used in most of the 

 experiments is shown in fig,. 1. The walls are maintained 

 at a potential (about 500 volts) high enough to send a 

 saturation current through the gas to the electrode which is 

 connected to a Wilson tilted electroscope and initially earthed. 

 The vessel stands on blocks of slate and is usually heated by 

 a small gas flame placed underneath it. Since it is of the 

 utmost importance that the insulation through which the 

 electrode passes should be kept cool, the tube carrying that 

 insulation is surrounded by a w 7 ater-jacket through which 

 a slow stream of water passes. This device was found to 

 simplify considerably the effects observed. 



3. The investigation has been hampered by the difficulty 

 of obtaining consistent results. Indeed the attempt to obtain 

 quantitative consistency has been abandoned and a general 

 constancy in the nature of the changes observed accepted as 

 the most satisfactory condition possible. The almost in- 

 variable sequence of changes when the vessel is first heated 

 and then cooled may be summarized as follows. 



^S attire of the Changes. 



4. When the source of heat is applied to the vessel the leak 

 through the latter increases temporarily but falls to its former 

 value in a period of the order of a minute : this period is 



* Communicated "bv the Author, 

 f Phil, Mag. April 1905, p. 545. 



