462 Mr. C. T. B, Wilson on Condensation Nuclei. [Feb. 19, 



is between 1-25 and 1-31 a fog or a mere shower is obtained, 

 according as the direction of the field is such as to drive negative or 

 positive ions upward. 



The ions are by no means the only nuclei which can be produced 

 within moist air from which the dust particles have been removed. 

 Among the most interesting of such apparently uncharged nuclei are 

 those produced in moist air exposed to ultra-violet light. It is 

 impossible in the time available to do more than allude to them 

 here. 



[C. T. R. W.] 



