Radioactivity of Sea- Water. 387 
amount of radium given in any evaluation known to me, I 
naturally regarded as requiring confirmation. 
In the month of May I received from Mr. S. W. Kemp, 
of the Trish Fishery Department, 2800 c.cs. of sea-water 
taken in the Irish Channel a few miles to west of the Isle of 
Man, lat. 53° 53' N., long. 5° 16' W. This also was trans- 
mitted in bottles which I had supplied for the purpose. The 
water was evaporated down to about 800 c.cs., and when 
investigated yielded only 0"0O38 x 10~ 12 gram per gram. 
This figure seemed to support sea-salt determinations ; but 
I was so convinced of the genuineness of the first result that 
I provisionally concluded a real difference to exist between 
near-shore and more open-sea samples of water. I had, 
indeed, changed the mode of extraction of the emanation, 
substituting a method in which ebullition proceeds in a 
partial vacuum, and at its conclusion the space above the 
liquid in the flask is completely filled with distilled water, 
thereby securing that every trace of emanation is displaced 
into a receiver, from which it is transferred into the electro- 
scope. I had found by comparative experiments on known 
quantities of uraninite in solution, that this mode of extraction 
gives a somewhat lower constant for the electroscope, showing 
that it is capable of effecting a more complete extraction. 
The change in manipulation was therefore in favour of giving 
a higher, and not low r er, result. 
Shortly after this measurement, Mr. Kemp sent me three 
other samples of sea-water. Calling the two samples already 
referred to (a) and (b) respectively — 
Sample (e) is from lat. 51° 26' N., long. 12° 5' W. A 
point about 65 miles due west of Valencia. Quantity, 
2665 c.cs. 
Sample (d) is from 1*5 miles south of Crow Head, Co. 
Kerry. Quantity, 2740 c.cs. 
Sample (e) is from lat. 51° 35' N, long. 10° 43' AY.— that 
is, about twenty miles west of Bantry Bay. Quantity, 
2764 c.cs. The last two samples were collected on the same 
day, June 21st. 
These were evaporated down as before, each to about 900 
or 1000 c.cs. The results were as follows : — 
0) 0-0126 x 10~ 12 . 
(d) 0-0152 x 10" 12 . 
0?) 0-0268 x 10- 12 . 
It will be seen that all these figures are of the same order 
of magnitude as the result on the Valencia water. The dis- 
crepancy with the Isle of Man sample is considerable. While 
