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XLIV. On the Residual Ionization in Air enclosed in a vessel 

 of Ice *. By. Professor J. C. McLennan, F.E.S., and 

 Mr. H. G. Murray, B.A.f 



[Plate V.] 

 I. Introduction, 



IN the course of a series of experiments on the ice of 

 Toronto Bay, Lake Ontario, McLennan and Wright J 

 found that the ionization in air confined in a vessel of the 

 purest zinc obtainable was about 4*4 ions per cubic centi- 

 metre per second. In this case the capacity of the vessel 

 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 ionization in air enclosed 

 in a vessel of about the same size and made of the same 

 metal. Still later, McLennan and McLeod ||, when working 

 w r ith a zinc Wolff electrometer of 2 litres capacity, found the 

 ionization 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 McLeod H have shown that on 

 the land at Toronto, at Bowland, 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 penetrating 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 a conductivity of about 4 ions 

 per c.c. per second must be accounted for in air confined in 

 a zinc vessel by (1) ionization by the collisions of air 

 molecules in thermal agitation, or (2) ionization occurring 



* Read before the Royal Society of Canada, May 26th 3 1915. 

 t Communicated by the Authors. 



X McLennan, Phvs. Rev. vol. xxvi. No. 6, June 1908 ; Wright, Phil. 

 Mag. xvii. p. 295 (1909). 



§ Simpson and Wright, Proc. Roy. Soc. No. 85, p. 175 (1911). 

 j| McLennan and McLeod, Phil. Mag. Oct. 1913, p. 740. 

 51 McLennan and McLeod, loc. cit. 

 ** Simpson and Wright, Proc. Roy. Soc. No. 85, p. 197 (1911). 



