140 G. F. BECKER RELATIONS OF RADIOACTIVITY TO COSMOGONY 



■\Yhile there are liraitations to the possible thickness of a uniformly 

 radioactive layer, there are also reasons for believing that radioactivity is 

 not uniformly distributed, and that it is at a maximum not more than a 

 few thousand feet from the solid surface of the earth. 



In this connection the radioactivity of the ocean presents points of 

 great interest. Mr Strutt '*^ and Mr A. S. Eve " have made determina- 

 tions of the activity of sea salt and Mr J. Joly ''^ of abysmal sediments. 

 Mr Eve finds that sea water does not contata per gram more than 

 6 X 10"'*^ grams radium, or only a three-thousandth part as much as 

 Mr Strutt's igneous rocks, and he infers that the uranium denuded from 

 the land is deposited in the oceanic sediments. Mr Joly obtained from 

 Sir John Murray globigerina ooze from a depth of 1,990 fathoms and 

 red clay from 2,740 fathoms. The former contained 6 times as much 

 radium as Mr Strutt's igneous rocks and the latter 16 times as much. 



The activity of the ocean itself is almost negligible. Its average depth 

 is about 3,440 meters (Woodward) and its density 1.027 Clarke), so that 

 the weight per square centimeter is 353,300 grams. Dividing by 3,000 

 gives the weight of Mr Strutt's rock, which would be radioactively equiva- 

 lent, and dividing agaia by 16 gives the corresponding weight of Mr 

 Joly's clay. If the density of this clay is supposed to be 2.75, it follows I 

 that the whole ocean has a radioactivity no greater than that of a layer 

 of clay 27 millimeters, or a trifle over one inch in thickness ! 



If radium emanation were a permanent gas, ocean water would be 

 charged with it, according to Henry's law; but the half -value period of 

 radium emanation is only 4 days and its average life therefore 5.8 days. 

 In so short a time as six days this heavy gas, liberated at or beneath the 

 ocean bottom, would diffuse vertically through the water to a short dis- 

 tance only, and, since its non-volatile products appear substantially in- 

 soluble in sea water, they would subside again to the bottom. In this 

 way it would seem that a concentration of radium D and subsequent 

 members of the series, including lead, must take place. As a matter of 

 fact, an extremely careful analysis "^^ has been made in the laboratory of 

 the U. S. Geological Survey of a composite sample of red clay prepared 

 by Sir John Murray from 35 specimens, and it showed 80 X 10~® grams 

 lead oxide per gram of clay. If any considerable part of this lead re- 

 sulted from the disintegration of radium, it is substantially certain that 

 concentration has taken place; for the equivalent amount of radium is 



''" Proceedings of the Royal Society of London, series A, vol. 78, 1906, p. 150. 

 " Philosophical Magazine, vol. 13, 1907, p. 248. 

 " Nature, vol. 76, 1907, p. 8. 



"F. W. Clarke: Proceedings of the Royal Society of Edinburgh, vol. 27, jiart Hi, 

 1907, p. 167. 



