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II. 



lONISATIOX IX MOIST AND DEY AIE. 

 By PEOFESSOE J. J. NOLAN, M.A., D.Sc, 



J. T. HAEEIS, M.Sc, 

 University College, Dublin. 



[Eead December 1-2, 19-21. Publislied Feercaky 16, 1922.] 



Is a previous paper^ an account has been given of an examination by one of 

 us of the ionisation procbicecl in moist air by a radio-active source. The 

 method employed was of high resolving power, and served to show that the 

 ordinary small ions consist for the gi'eater part of four distinct groups, each 

 group having a definite mobility, the values being roughly 2, 1-8, 1-5, and 

 l-35cm./see. in a field of 1 volt/cm. In addition, other groups present in 

 small quantities were detected, the most mobile of these having a mobility 

 value of about 12. Ions of this type had been already discovered in the 

 ionisation produced by breaking up water.- The present paper gives the 

 results of a more complete examination by the same method of the ionisation 

 in moist air and of a brief examination of the ionisation in carbon dioxide. It 

 also deals with the examination of moist and very dry air by the method of 

 Eutherford and Franck. It is convenient to distinguish the two methods as 

 the " air-current method " and the " alternating field method." 



Examination of the Ionisation in Moist Air hy tJie Air- Current Method. 



This method has been already described, and for fuller details of the 



apparatus, etc., the reader is referred to the previous paper already cited. 

 Air is drawn between two parallel plates, close to one of which is a small 

 space exposed to a fairly intense ionising radiation. The source of the 

 radiation is a number of thin glass tubes containing the decay products 

 of radium emanation. The plate close to which the ions are produced is 

 charged up to various potentials, and the corresponding currents to the other 



' J. .J. Nolan, Proc. Royal Irish Academy, Sect. A, vol. xxxv, 1920. 

 " J. J. Nolan, Proc. Royal Society, Sect. A, vol. xciv, 1918, 



E.I. A. PKOC, VOL. XXXVI, SECT. A. [3] 



