[WRIGHT] VARIATIONS IN THE CONDUCTIVITY OF AIR 



99 



also at a number of points on land on the south side of Lake Ontario, 

 between Queenston Heights and Niagara Falls. These results are 

 recorded in Table IX. 



TABLE IX. 



Comparison of conductivity experiments made on Steamer " Corona " 

 with those made on land. 



Mean of results of land 



experiments = 42 .3 ions^per cc. per sec. 

 Mean of results of steamer 



experiments = 35 .6 ions per cc. per sec. 

 Difference = 6.2 ions per cc. per sec. 



From the table it will be seen that the ionization at different points 

 on the limestone soil of tho Niagara District was practically constant. 

 It will be seen, too, that the ionization obtained about 42 metres under- 

 ground at the Falls was practically the same as that obtained at the 

 purface on the limestone ridge. We see also from the figures that the 

 screening action of the lake minus any effect due to an intrinsic radia- 

 tion from the boat itself is represented by the value of 6.7 ions per cc. 

 per sec. with the particular lead cylinder used. From the figures which 

 are given later in Table X it will be seen that the screening effect of 

 the lake in a cylinder of lead in the condition of that used in the above 

 experiment is represented by 9 ions per cc. per sec, which shows that 

 approximately 2.3 ions per cc per sec must have been due to a radia- 

 tion emitted by the steamer or by its contents. 



