McClelland and M' Henry — Uncharged Nuclei. 297 



nuclei regained that property after a certain interval and under certain 



conditions. The following experiments will be quoted as examples. 



A glass tube was strongly heated in a Bunsen flame and " fatigued." It 



was left open, exposed to the atmosphere for a few days. When again 



C 

 examined it had recovered, the ratio -^ being almost as great as when 



the tube was fresh. Heating for fifteen minutes suffices to drive off nearly 



Q 



all the nuclei, the value of ^ falling off almost to unity. 



It might be expected that the effect would be recovered immediately on 

 cooling. This is not the case, nor is the effect recovered if the tube is left in 

 the apparatus overnight closed in. Thus seA^eral glass tubes which had been 

 fatigued were found not to recover if left for several days in the apparatus 

 closed in, but recovered fully if left overnight fully exposed to the 

 atmosphere. 



The nuclei driven off by heat from glass tubes can also be charged by 

 exposure to ultra-violet light. The apparatus is in this case identical with that 

 described in the previous expei'iments. The uranium is, of course, excluded. 

 The tube is heated, and the nuclei so obtained are exposed during tlieir 

 passage through the quartz tube to the ultra-violet light of the spark, which 

 is a few mms. distant. A current voltage curve for the positive ions thus 

 obtained gave a mobility of "0009. 



When a tube is heated and fatigued, as above described, the nuclei which 

 can be charged by passing over uranium are recovered in about twenty-four 

 hours when the tube is exposed to the atmosphere. The property of emitting 

 nuclei, which could be charged by ultra-violet light, is not regained so rapidly. 

 Thus a tube which recovered in twenty-four hours the property of emitting 

 nuclei which were chai'ged by the uranium small ions gave off no nuclei 

 which could be charged by ultra-violet light. The latter property, however, 

 it regained in about a week. It may be that the nuclei are not acted upon 

 by ultra-violet light until they reach a certain size, and that in the initial 

 stages of recovery of a glass tube the nuclei given off are small. 



The ultra-violet effect is probably due to the photo-electric emissions of 

 electrons from rather big particles. If this is the case, we should expect that 

 many of the electrons would be lost by diffusion to the sides of the vessel 

 before becoming attached to neutral particles. We should thus expect the 

 positive numbers to be greater than the negative. 



An experiment was performed with a new glass tube to investigate this 

 point. Positive and negative numbers were taken alternately, the spark 

 running continuously, and the tube heated for each reading at a different 



gOJENT. PROC, R.D.S., VOL. XVI., NO. XXIV, 2 P 



