318 Conductivity of Air enclosed in Metallic Receivers. 



the receivers used in this investigation was due to residual 

 active impurities and to intrinsic activity in the metals o£ the 

 receivers. 



(4) Based on this fact, a determination has been made 

 of the ionization in free air due to radioactive impurities in a. 

 clay soil, and this value 0*9 ions per c.c. per sec. has been 

 found to be in close agreement with a value deduced by 

 Strong from Strutt's determination of the radium content of 

 the earth. 



(5) The ratio of the ionization in cylinders of lead, zinc,, 

 and aluminium due to the radiations from the earth has been 

 determined, and has been found different from the ratio for 

 the ionization due to the gamma rays from radium ; a result 

 which needs confirmation but which points to a difference in 

 the penetrability of the two radiations. 



(6) The values obtained in the open for the ionization in 

 well cleaned receivers of lead, zinc, and aluminium are lower 

 than any hitherto recorded, the numbers 8'6, 6*0, and 6' 5 

 respectively being obtained over the water of Lake Ontario. 



Considered as a whole, the experiments described above are 

 interesting from the light which they throw on the question 

 of the radioactivity of metals and substances generally. The 

 values obtained for u 'q" for the three cylinders at Station 2, 

 Table XI., differ from each other but little. They are more- 

 over of the order of magnitude of effects which might easily 

 be accounted for by active impurities in the metals, since 

 differences as large as these values of " q " may easily be 

 obtained with cylinders made from different samples of 

 almost any metal selected at random. Considering also the 

 difference in the atomic weights of the three substances, 

 aluminium, zinc, and lead, and having in mind that radio- 

 activity is a property associated with atomic structure, it 

 would seem that, if these metals could be obtained entirely 

 free from active impurities, and the conductivity of air con- 

 tained in vessels made from them studied, it would be found, 

 if the observations were carried out under conditions or in 

 places where no ionization was possible from penetrating 

 radiations arising from external sources, to drop to a very 

 low value if it did not entirely vanish. 



In conclusion, I desire to thank Professor McLennan, botk 

 for his valuable suggestions and for his assistance at all times 

 throughout the investigation. 



