the Atmosphere over the Ocean. 253 



(3) Emanation, and its successive products, rising from 

 radium in the land, and carried by wind to mid- 

 ocean. 



(■1) Charged particles due to the action of wind on the 

 waves. 



(5) Charged particles due to the change of area occasioned 

 by waves or ripples. 



Before considering these it is desirable to obtain an estimate 

 of the amount o£ radium in sea-water. Now Strutfc has 

 found, as an approximate determination, that sea-salt contains 

 •15 x 10~ 12 grams of radium per gram of sea-salt, whilst his 

 average value for 17 specimens of sedimentary rocks is 

 2 2 x 10~ 12 grams of radium per gram of rock. So that 

 such rocks are about 15 times as active as sea-salt. But 

 sea-salt forms about one-thirtieth part of the total constituents 

 of sea-water, and we may therefore deduce that on the 

 average a gram of rock contains about 450 times as much 

 radium as a gram of sea-water. 



The writer also has measured the amount of radium both 

 in sea-salt and sea-water. The method employed was similar 

 to that described by Strutt; and the standard used was a 

 solution of radium bromide prepared by Dr. Boltwood, and 

 of such quality that radium bromide gave per gram a heating 

 effect of 110 grain-calories an hour. Four hundred grams of 

 Omaha sea-salt, guaranteed pure by the importers, gave 

 2*04 x 10~ u grams of radium. This value is one-seventh of 

 that obtained by Strutt. It appears then that 1 gram of sea- 

 water should contain about 6 x 10 -13 grams of radium. 

 Again. Mr. C. H. T. Xewton of Edinburgh University was 

 good enough to collect some sea-water in mid-Atlantic 

 between Montreal and Glasgow, and to forward it to me 

 sealed in clean glass bottles. This water was boiled down, 

 and in due course the emanation from 2500 c.c. of sea-water 

 was collected and examined in an electroscope. The amount 

 measured was very small and is that due, per gram of sea- 

 water, to about 3 x 10 — 16 grams of radium. From these two 

 experiments it appears safe to conclude that sea-water does 

 not contain more than 6 x 10 -16 grams of radium per gram of 

 water, or only a three-thousandth part of the average 

 determined by Strutt in various sedimentary rocks. It seems 

 clear that the uranium denuded from the land and carried to 

 sea by rivers sinks to the bottom of the ocean and ultimately 

 gives rise to the supply of radium found in sedimentary rocks. 

 And this view is supported by the results which Strutt found 



Phil. Mag. S. t>. Vol. 13. No. 74. Feb. 1 ( J07 T 



