[eve] radioactive SUBSTANCES IN THE EARTH 135 



It is somewhat difficult to account for these variations at sea, as 

 the radium contents of seawater are minute. (Satterley Proc. Camb. 

 Phil. Soc.) They may possibly depend on the radium contents of the 

 ship. 



As regards land observations, the variation against the barometer 

 may be now regarded as established, at least with the vessels not her- 

 metically sealed. 



In the case of vessels not tightly closed, there is the possibility 

 that the emanation may diffuse into the testing chamber and the direct 

 effect of the a particles within may be as important as the y radiation 

 from without. In order to determine the relative magnitudes of these 

 two causes it would be necessary to compare two vessels, one sealed 

 the other not, at the same time, on two different electroscopes. 



Shortly after writing the above sentence, I found that this experi- 

 ment had been tried by E. V. Schweidler* at Seeham, with a zinc 

 vessel not sealed, and a copper vessel, hermetically sealed, on shore 

 and above the shallow water of Lake Mattsee. The two apparatus 

 did not agree, even when close together. This disagreement, unless 

 due to diffusion of large ions, may be clue to emanations diffusing into 

 the unsealed vessel. 



Since the known amount of emanation in the air is subject to 

 variations as large as 1 :5 or 1:10 (Eve, f Satterley %) , and since the aver- 

 age amount of emanation present is capable of producing 2 or 3 ions 

 per cm^ per sec. due to ionization by a rays, it is clear that a variation 

 of '3 to «7 in the value of q may be expected. The diffusion of large 

 ions, if pronounced, might be a more potent agent in diminishing 

 ionization within the unsealed vessel. 



Nevertheless it must be remembered that Wulf obtained the 

 variations against the barometer, with vessels carefully closed and made 

 tight with tap grease, and he attributes the fluctuations to the rise and 

 fall of the emanation to the upper layers of the ground, as the atmos- 

 pheric pressure decreases or increases, with consequent deposit of 

 radium C at different levels. 



*Akad. Wiss. Wien. Ber. 121. pp. 1297-1304! 

 tPhil. Mag. Dee. 1907. 

 ÎPhil. Mag. July 1910. 



