Imclennan MCLEOD] EARTH'S PENETRATING RADIATION 33 



Ocean with the Wilson Electrometer, goes to shew, as one might have anti- 

 cipated, that it is quite impossible to take readings on ship board with an 

 instrument provided with a gold leaf system with any degree of accuracy. 



In the course of the observations at Toronto, values between 9 

 and 10 ions per cc. per sec, with a mean of 9-47, were obtained when 

 the readings were taken in a residential building, the walls of which 

 were constructed of red brick. 



As values close to 8-62 for "q" were always obtained in the 

 Physical Laboratory, which was constructed of stone and white brick, 

 and as these values were uniformly lower than those obtained in the 

 residence referred to it was thought that possibly the higher values 

 might be due to a measurable excess of radioactive matter contained in 

 the bricks of the residential structure. 



As the bricks for both structures were made from different deposits 

 in the same brick-yard a series of measurements was made in the 

 neighborhood of these different deposits and it was found that the 

 surmise was correct. 



In this particular brick-yard the surface layer is a sandy loam 

 about one metre thick and below these there is a series of strata of glacial 

 clays, each stratum ranging from 4 to 10 metres in thickness. Below 

 the clay is a deposit of Lorraine shale some 200 metres in depth. This 

 brick-yard which has been worked for over fifty years, now consists 

 of a great opening in the face of a hill and a huge cylindrical cavity in 

 front of this opening and extending down into the shale. The depth 

 of the cavity at present is about 25 metres and the length of its dia- 

 meter is about the same. The sides of the opening in the face of 

 the hill as it stands consist of a series of terraces, each of which 

 consists of one particular deposit of clay. This system of terraces 

 in the clays provided an excellent means of investigating the 

 radiation from each deposit in turn and when readings were taken 

 on each terrace it was found that these gave values for "q" extend- 

 ing from 8 to 9 ions per cc. per sec. with a mean value of about 8 «84, 



In the shale pit, however, much higher readings were obtained. 

 These were taken at different points on the base of the pit and on a 

 number of ledges which were accessible. The values found for "q" 

 in the shale pit ranged from 12 to 14-8 ions per cc. per sec, the lower 

 values being obtained when the stations were taken at points near 

 surfaces which were weathered and the higher ones were the observ- 

 ation stations were close to places where the surface of the shale had 

 been recently exposed. 



As an illustration of how definitely the comparatively strong 

 radiation from shale producing the high ionization was localized, a 

 particular measurement may be cited. 



