﻿in the Earth and the Atmosphere. 195 



that made for the atmosphere (3), we have 



4ttQ'K' 

 ~ \' 

 W "092x9 



••• Q , =^ = 4..3 6 xlO- = 1 - 8Xl °- U - • ^ 



111 this case K' has been taken as for a zinc or copper vessel 

 (Table I.), because these would involve some secondary 

 radiation to an extent approximately the same as brass. 



It is interesting to compare this value of the equivalent 

 amount of radium bromide per c.c. of the earth's crust near 

 the surface, found by measurement of the penetrating 

 radiation, with that deduced by Professor Rutherford from 

 consideration of the earth's temperature gradients. His 

 result is about seventy times as small, or 2'6 X 10 -13 , also 

 expressed in terms of radium bromide. But Strutt has just 

 published a paper*, stating that he finds by direct observation 

 of rock-specimens that the radium present in the upper 45 

 miles of the earth's crust is alone sufficient to account for 

 the existing temperature gradients in the earth. This indicates 

 that he finds actually present thirty times as much radium as 

 Rutherford showed was necessary to account for the earth's 

 temperature gradients on the assumption that radium was 

 distributed uniformly throughout the whole earth. In fact 

 Strutt finds about 8*5 X 10~ 12 grams of radium bromide, in 

 equilibrium, as the average equivalent of the active matter 

 per c.c. of the earth's crust. But this result needs a further 

 correction, because Rutherford and Boltwood state f that 

 1 gram of uranium is associated with 3*8 x 10~ 7 grams of 

 radium, not with 7*4 x 10 -7 as previously stated. Therefore, 

 from Strutt's investigations we may conclude that 4*25 x 10 -12 

 grams of radium bromide is a fair average measure of the 

 active matter per c.c. of the earth's crust, and this result is 

 four times as small as the amount which I have calculated as 

 sufficient to account for the penetrating radiation. The dis- 

 crepancy is not large considering the uncertainty of the 

 distribution of active matter in the earth's crust J. 



It will be seen, therefore, that whilst the active matter in 

 the earth is of the right order to account for the observed 

 magnitude of the effects of penetrating radiation, that in the 

 atmosphere is not sufficient to do so. This conclusion is capable 



* Proc. Roy. Soc, A. vol. lxxvii. 

 t American Journal of Science, July 1906. 



X Measurements of the penetrating radiation in various mines would 

 lead to a valuation and survey of the active matter in the earth's crust. 



02 



