Section III., 1915 ll05] Trans. R.S.C. 



On the Residual Ionisation in Air Enclosed in a Vessel of Ice. 

 By Professor J. C. McLennan, F.R.S., and Mr. H .G. Murray, B.A. 



(Read May Meeting, 1915). 



I. Introduction. 



In the course of a series of experiments on the ice of Toronto bay. 

 Lake Ontario, McLennan and Wright^ found that the ionisation in 

 air confined in a vessel of the purest zinc obtainable was about 4-4 ions 

 per cubic centimetre per second. In this case the capacity of the ves- 

 sel was about 30 litres. Later on in the course of their voyage to the 

 South Pole, Simpson and Wright- found a value of 4-1 ions per c.c. 

 per second for the ionisation in air enclosed in a vessel of about the 

 same size and made of the same metal. Still later, McLennan and 

 McLeod^ when working with a zinc Wolff Electrometer of 2 litres 

 capacity found the ionisation in air to be 4-33 ions per c.c. per second 

 on the Atlantic Ocean, 4-93 ions per c.c. per second on the surface of 

 Lake Ontario and 4-77 ions per c.c. per second, eight metres under 

 the surface of Lake Ontario where the water was 20 metres deep. 



Further, McLennan and McLe d^have shown that on the land 

 at Toronto, at Rowland, Scotland, at Cambridge, England, and at 

 Braunschweig, Germany, the conductivity of air enclosed in a zinc 

 Wolff Electrometer was represented by the generation of about 8-5 

 ions per c.c. per second. Moreover Simpson and Wright^ have shown 

 that Joly's numbers for the amount of radium in sea water make it 

 clear that over the sea the total number of ions which can be generated 

 per c.c. per second in air confined in a zinc vessel by the total penetrat- 

 ing radiation from terrestrial sources including air, land and water 

 must be less than 0-1. As the conductivity of the air in a zinc vessel 

 on and in the waters of Lake Ontario was practically the same as it 

 was on the ocean it follows that conductivity of about 4 ions per c.c. 

 per second must be accounted for in air confined in a zinc vessel by 

 (1) ionisation by the collision of air molecules in thermal agitation 



'McLennan. Phys. Rev. No. 6, Vol. XXVI, June, 1908. Wright. Phil. 

 Mag. 17, p. 295, 1909. 



2 Simpson and Wright. Proc. Roy. Soc. No. 85, p. 175, 1911. 



3 McLennan and McLeod. Phil. Mag. p. 740, Oct., 1913. 

 * McLennan and McLeod, loc. cit. 



5 Simpson and Wright. Proc. Roy. Soc. No. 85, p. 197, 1911. 



