42 



Proceedings of the Royal Irish Academy. 



quantities, of four groups of ions. Observing the critical voltages, we can, 

 as before, calculate the mobilities. We find for the negative ions the values 

 2-0, 1-7S, lo4, and 1-36; and for tlie positive, the values 2-07, 1-78, 1-59, • 

 and 1"45. Some of these steps are nuich more distinctly marked tluin others. 

 For example, in the case of the negative ions, the steps corresponding to the 

 two faster ions (20 and 1'78) are much greater than those corresponding to 

 the other two classes. In the case of tiie positive ions, however, the slowest 

 ion (1"45) comes out mucli more distinctly than the others. 



fJeaativer 



J>-^, 



■ Volts. - 



'1 



Fio. 3. 



There can liardiy be any doubt as to the intei-pretation of these curves. 

 They show that when ionization is produced in moist air by radio-active sub- 

 stances the bulk of the ionization is carried by ions of four distinct classes, 

 having mobilities 2-0, 178, r56, and 140 approx. That among negative 

 ions the two faster groups tend to predominate, while among positive ions 

 the slowest kind carries a large part of the ionization. 'J'hat, in addition, ions 

 of mobility up to 12o are present in distinct groups, but in small quantities. 



