Earth's Penetrative) Radiation at JJifermf Altitudes. 641 

 Table II. 







The ice on 







The Physical 

 Laboratory. 



The lawn, 



University 



campus. 



Toronto Bay. 

 Depth of water 



5 metres. 



Distance from 



shore =400 



metres. 



Basement of 



City Hall. 



Engineer's 



room. 



City Hall 



Clock Tower, 



64 metres 



high. 



152 



151 



9-3 



165 



11-9 



153 



15-2 



92 



15-9 



122 



155 



15-0 



8-9 



152 



11 -6 



14-9 



■ 15 2 



9-0 



157 



127 



151 



151 



9-8 



163 



11-8 



15-5 



152 



90 



16-6 



124 



14 





98 



169 



122 



149 





9 4 



15-7 



11-8 



152 





98 



15-5 



121 



15 8 





9-1 



164 



12 4 



Mean = 15*2 



Mean =151 



Mean = 9-3 



Mean = 16-1 



Mean = 12 1 



The observations made in a room in the basement of the 

 city hall, it will be seen, gave a mean for "q" of 161, while 

 those made at the top of the clock tower on the building 

 64 metres from the ground, gave a mean of only 12*1 ions 

 per c.e. per second. 



From the evidence adduced by C. S. Wright * it would 

 appear that the ice and water in Toronto Bay cuts off' practi- 

 cally all the penetrating radiation from the ground beneath. 

 Assuming this to be so, we obtain from the numbers given in 

 Table II. the value 5'8 for the number of ions made per c.c. per 

 second, in the air in the receiver by the penetrating radiation 

 present at the lawn, as well as by the secondary rays produced 

 by this radiation at the metallic walls of the receiver, and 

 probably, too, at the surface of the ground. 



The table shows also, with the same assumption, that 2'8 

 represents the value for " q " arising from the penetrating 

 radiation present at the top of the city hall tower and from 

 the secondary rays excited by it. These numbers show that 

 the effect of the penetrating radiation and its accompanying- 

 secondary radiation in ionizing the air in the receiver at the 

 top of the tower, w T as only about 48 per cent, of the effect 

 produced by similar radiations on the university lawn. 



* Loc. tit. 



