Nolan and Harris — lonisation in 3Ioist and Dry Air. 49 



criticized by Kia-Lok Yen,' who found that on repeating Haines' experiments 

 he was unable to find clear indications of any ion of abnormal mobility other 

 than the free electron. It is possible that an initial condition of very good 

 drying was present in Haines' experiments and was not attained l)y Yen. 



Brief Summary. 



1. The composite nature of the ionisation in moist air has been demon- 

 strated by two methods. 



2. The effect of extreme drying has been investigated. The effect on 

 negative ionisation is to increase the numbers of ions of the more mobile type, 

 and to cause the disappearance of the ordinary ions. "With positive ionisa- 

 tion the more mobile ions are also found in greater numbers, but the ordinary 

 ions are still present. 



3. Doubly charged positive ions are found in very dry air. 



4. Some indications are obtained of the presence of free electron!?. 



NOTE ADDED IN PEOOF. 



We have since found a paper by W. Altberg, Ann. de Phys. 37, p. 849, 

 1912, " IJber monomolekulare Elektrizitatstrager . . ." Altberg finds in air 

 and CO2 negative ions of mobilities lO'l and 5'8 respectively. 



'Kia-Lok Yen, "Phys. Rev.," si, 1918. 



R.I.A. PKOC, VOL. XXXVI, SECT. A. \p\ 



