424 Prof. McLennan on Induced Radioactivity 



exposed wire, the electrical machine necessary in the Toronto 

 experiments was not employed. 



In testing for induced radioactivity, the wire was exposed 

 for periods of about two hours and was removed in sections, 

 each section being replaced by a new length. The same 

 method of testing was used as in Toronto, and the results 

 exju-essed in terms of the standard radioactive substance. 



Exposures were made on four different days with the 

 following results, A, B, and C denoting the sections of the 

 wire of which A was that nearest the observing station, and 

 C that nearest the Falls : — 



Date. 



Section of 

 wire tested. 



Induced Badioactivity. 



Saturation current of 



standard substance = l. 



Sept. 12th 



A. 

 B. 

 C. 



A. 

 B. 

 C. 



A. 

 B. 

 C. 



A. 

 B. 

 C. 



0-1 



031 

 None observed. 



0-16 

 None observed. 

 Not exposed. 



013 

 0-14 

 Oil 



0-15 



0-12 



None observed. 



Sept. 13th 



Sept. 16th 



Sept. 17th 





From these numbers it will be seen that but little variation was 

 observed in the radioactivity excited in the sections A and B. 

 In C, however, w T hich was nearest the Falls, measurable radio- 

 activity was present in only one of three exposures. 



Ordinarily this section was drenched by masses of falling 

 water in addition to being surrounded by fine spray such as 

 enveloped the rest of the w T ire. But on Sept. 16th the air 

 currents, during exposure, were such as to drive aside the 

 sheets of water and permit only the fine spray to come in 

 contact with the section. 



As already stated the spray enveloping the section B was 

 generally heavier than that in contact with A, but the con- 

 dition was not permanent as the spray was blown about by 

 gusts of wind whose direction was continually changing in 

 the gorge. 



The chief interest attaching to the results was that the 

 radioactivity excited was much less than that in Toronto. It 



