402 Variation of Radioactivity of Hot Springs at Tuwa. 



water had undergone a change. We found that the supply of 

 water from the springs was considerably less than in December 

 1910. There bad been no rain during December, January, 

 February, March, and April. The actual strength of the 

 flow, however, was not measured. The radioactivity of the 

 hot spring was examined in the same way and with the same 

 instrument as in December 1910. We obtained the following 

 results : — 



Saturation current 15137 M.U. 



Radioactivity 6206xl0~ 9 C. 



Thus the radioactivity of the hot spring was almost double 

 of what it had been in December. For want of time the cold 

 spring was not examined on this occasion. 



Here, then, we find the greater radioactivity when the 

 spring yields less water. This result can be accounted for 

 by considering the local conditions. 



The cold spring showed practically the same radioactivity 

 as the hot spring. This seems to indicate that at Tuwa the 

 radium -bearing rock is near the surface, as the cold spring- 

 is not likely to come from a great depth. 



Moreover, the radioactivity of the neighbouring wells 

 decreases with their distance from the springs. Three wells 

 were examined for radioactivity in April 1911*. 



1st well. Distance from the hot spring about 200 metres. 



Saturation current 19*85 M.U. 



Radioactivity 7-98xl0" 9 C. 



2nd well. Distance from the hot spring about a quarter 

 of a mile. 



Saturation current 8'1 M.U. 



Radioactivity 3'26 x 10" 9 O. 



3rd well. Distance from hot spring about half a mile. 



Saturation current 7*2 M.U. 



Radioactivity 2*89 x 10~ 9 C. 



We cannot lay much stress on the difference between the 

 second and the third well. The difference in their radio- 

 activities can be fully accounted for by the fact that the 

 second well was not much used, whereas the third well, 

 which is situated at the railway-station, was much resorted to. 

 One result, however, stands out quite clearly : there is a 

 distinct drop in the radioactivity of the water as we move 

 away from the hot spring. This seems to justify the con- 



* Indian Medical Gazette, December 1912. 



