254 Mr. A. S. Eve on the Ionization of 



for igneous and sedimentary rocks, because the average 

 amount of radium present is approximately the same in the 

 two cases. 



If the amount of radium present in the sea is so small, it is 

 certain that the amount of emanation rising from the ocean 

 must be much less than that from the land. 



Similar conclusions may be arrived at with respect to the 



penetrating radiation due to the active matter in the ocean. 



The coefficient of absorption of the 7 rays of radium by 



water* equals '034, and since rocks are about 2*7 times a& 



heavy as water, the coefficient of absorption by rock is 



about *092. In other words, the 7 rays are reduced to half 



value after penetrating 7*5 cms. of earth, or 20*4 cms. of 



water. But if there is 500 times as much radium in the 



average rock as in sea-water, we should find the penetrating 



2*7 

 radiation over the ocaan to be ^77 times that over land. But 



oOO 



Cooke has shown that the penetrating rays at Montreal 



produce 4 or 5 ions per c.c. per second. Hence at sea the 



penetrating radiation should be 135 times as small and 



produce only '03 ions per c.c. per second. It may be noted 



that a crucial test of the character of the penetrating radiation 



could be made by proving such radiation entirely absent, or 



very minute, above the surface of the sea or of a large lake a 



few metres deep, at a distance of one or two kilometres from 



land. 



Again, the emanation arising from the radium in the land 

 must be carried by wind over the ocean. Now it is known 

 that cyclones sometimes cross the Atlantic in four or five 

 days, but in steady weather, when anticy clonic conditions 

 occur, the transportation of the emanation must proceed 

 more slowly ; the radium emanation decays to half value in 

 four days. Hence it would be expected that the ionization 

 over the ocean would be much less than on land. It is true 

 that Greenland is only 300 miles north of the course of the 

 "Athenia," but the results of Boltzmann were obtained at 

 more than a thousand miles from any large area of land. 



Mache and Rimmerf found ^ = 120 for the air in caves at 

 Vienna ; and in free air q has been found to vary from 9 

 to 38 J. But if a is equal to 1'lxlO- 6 , and ?* = i000, we 

 have seen that a value of </=! is sufficient to account for 

 the ionization observed over the sea. It must be remembered 



* McClelland, Phil. Ma?. July 1904. 



t Phys. Zeit. 15 Sept. 1906. 



X Schuster, Troc. Manchester Phil. Soc, Nov. 12, 1904. 



