Section III . 1913. [131] Trams. R.S.C. 



Azotes on the Penetrating Radiation due to Radioactive Substances in 



the Earth. 



By A. S. Eve, D.Sc, F.R.S.C. 



(Read May 28, 1913) 



In June, 1912, some measurements were taken in the Old Library of 

 the Macdonald Physics Building, McGill University, and large variations 

 were found in the so-called "natural ionization" of testing vessels placed 

 over a Wulf Electrometer. The variations fluctuated in magnitude 

 against the barometer, so that the ionization current was large when 

 the barometer was low, and conversely. The variations of q, the num- 

 ber of ions generated per cm^ per second, were from 12 to 22. The 

 results are shown in figure 1, where the upper curve gives the time 

 changes of the barometer, and the lower curve those of the ionization 

 current. 



Further measurements were made in the Autumn of 1912 in the 

 same room and with the same instrument, in every case using a testing 

 vessel which rested on the platform of the instrument, so that it fitted 

 closely, but was not hermetically sealed. With one strongly marked 

 exception (Sept. 14tli) for which I cannot account, the same effect 

 was observed. The ionization currents were large or small, as the 

 barometer was low or high respectively. The fluctuations in q were 

 betw^een 10 and 28 (See fig. 2) . No such large fluctuations were observed 

 out of doors, or in the Chemistry Building, and it appeared certain, 

 therefore, that the changes observed were due to emanations diffusing 

 into the old library from other parts of the Physics Building. If the 

 instrument was taken from the Physics Building into the Chemistry 

 Building, the high readings continued for some time, so that the emana- 

 tion was diffusing into the testing vessel and, with subsequent products, 

 producing the ionizing effects from within, and not mainly by means 

 of 7 rays penetrating the walls of the vessel. 



The chief radium preparations in the building are kept hermeti- 

 cally sealed, but there are many, smaller in quantity, which are not in 

 air-tight receptacles. It seemed then that the emanation escaped 

 more readily from these when the barometer fell, and diffused into the 

 library, and also the testing vessel. 



It occurred to me that similar effects might be detected out of doors, 

 on a smaller scale, due to the radium emanation diffusing from the 

 ground more readily at times of low atmospheric pressure. 



