142 ROYAL SOCIETY OF CANADA 



sensibility, and possibly, too, with auxiliary apparatus attached for 

 taking the readings automatically in place of taking them visually, 

 but time has not permitted and the further investigation of this point 

 has been of necessity deferred. 



VI.— SUMMARY. 



In summarising the results of the investigation the following are 

 the chief points which have been noted : 

 a With an open receiver. 



1. No daily regular maxima or minima conductivities were 

 observed. 



2. Changes in conductivity occurred from day to day which 

 seemed to be directly connected with concurrent barometric changes. 



3. The conductivity was found to be slightly less when the 

 ground was frozen and covered with snow, than when it was bare and 

 the temperature was above freezing point. 



b With a closed receiver. 



1. Larger variations in the conductivity were observed but no 

 regular diurnal maxima or minima values were noted. The larger 

 variations in the conductivity were attributed to a lack in the sensi- 

 tiveness of the measuring electroscope. 



2. Different metals which were used in the construction of the 

 receiver were found to possess different activities, zinc being very low. 



3. Atmospheric air, even when well filtered through cotton wool, 

 was found to contain many suspension particles. 



As a general result of the investigation it would appear that the 

 soil contributes by far the greater proportion of the penetrating 

 radiation present at the earth's surface at Toronto, and by comparison 

 any that may have its source in the atmosphere or in the sun may be 

 considered to be negligible in amount. 



In closing I wish to express my gratitude to Professor McLennan 

 for his kindness throughout the research, for suggestions and for 

 assistance in overcoming mechanical difficulties. 



My best thanks are also due Mr. E. F. Burton for his kindness in 

 taking a number of readings. 



