1248 Wisconsin Academy of Sciences, Arts, and Letters. 
the scale in volts was done by noting the position of the leaf 
corresponding to several values between 350 and 450 volts. 
The method of, standardizing the electroscope by means of 
uraninite, and other details of manipulation have been described 
in former publications. 2 * 
The computation of the activity is simple and is illustrated 
by the following example: In the test of Silver Spring it was 
found that the emanation obtained from 5.34 liters of water 
produced a maximum fall of the leaf of 12.65 divisions per 
minute. Hence the activity in terms of the uranium standard 
is given by,— 
12.65 X 7.5 X 10“ 4 
5.34 
17.7 X 10~~ 4 g. U = 67.3 X 10~ 11 g. Ra. 
In E. S. units the activity is,— 
12.65X1*7X9.4 
60 X 300 X 5.34 
21.2 X 10 -4 
The quantitative results of the examination are given in 
Table I. The fitst column gives the name of the spring or other 
source, the second its location, the third the date of collection, 
and the remaining columns the activities expressed respectively 
in terms of uranium, radium, and electrostatic units. These 
values represent the activities of the samples at the time of collec¬ 
tion. In several tests some hours elapsed between the collection 
and the electroscopic test. The decay in the activity of these 
samples was corrected for by the formula I 0 =It e rt , expressing 
the decay of the activity with the time. I 0 represents the initial 
activity, It the activity observed t hours after the water was 
collected, and r the radioactive constant of the radium emana¬ 
tion. The value of r used in the calculations was 0.0077, which 
is an approximate mean of the values of several investigators. 
2 Jour. Phys. Chem. 9, 320 (1905), and Trans. Am. Electrochem. 
Soc. Yol. 8, 292 (1905). 
