262 84 



The radio activity is thierefore more likely to be dependent on other proper- 

 ties of the springs, and curiously enough, it seems to increase with the height of 

 the springs above sea-level. 



Again, if the heat energy of the springs is produced by radium accumulated 

 around the subterranean seat of the springs, a greater amount of emanation would 

 probably be found in the spring gases than is the case. Of course, the emanation 

 takes a considerable time to pass through the channels of the spring from the 

 interior of the earth up to the surface, so that it is difficult to calculate how great 

 a fraction of the original emanation reaches the surface without being transformed. 



The radio activity of the German and Austrian mineral springs' seems to be 

 about the same as of the Icelandic springs. A few, for instance Grabenbächer- 

 quelle, which contains emanation amounting to 564 x 10"-' i?S£ = 267 per gram 

 of uranium per second, are even more radio active than the Icelandic springs. 

 This is generally the case in springs containing appreciable quantities of radio- 

 active substances in the spring water or in the sediments. It does not, however, 

 preclude the possibility of radium being an indirect cause of the thermal activity 

 of the hot springs. Strutt's'-' researches have rendered it probable that the internal 

 heat of the earth is sustained by the radium contained in common rocks. It is 

 true that no measurements have yet been made of the radium contained in the 

 Icelandic rocks, but there is no reason to doubt that they are similar in this res- 

 pect to the same sort of rocks in other lands. 



We examined the water from two cold springs in the neighbourhood of 

 Akureyri for radio activity. They turned out to be more radio active than the 

 tap water in Copenhagen. This example shows that the superficial rocks of Ice- 

 land may contain radium, but our measurements of the emanation in the hot 

 springs may also be considered as a proof of the presence of radium in the Ice- 

 landic rocks. I have already pointed out that the radium contained in the super- 

 ficial rocks may have considerable bearing on the radio activity of the hot springs. 

 But the radium in the lower strata has also considerable significance, in that some 

 of the emanation evolved in these rocks is carried bj' water, steam and other spring 

 exhalations to the main channel of the spring group. This has no little influence 

 on the activity of all the springs in the group, for the average radio activity of 

 a spring group depends on the amount of emanation supplied to the spring chan- 

 nel deep down in the earth where the springs of the group have all a common 

 channel, or where the different spring channels are so near to each other that they 

 are subject to the same influences. The emanation thus received by the channels 

 originates chiefly in the surrounding rocks, which are of course very deep down, 

 although some of it may be carried by the water all the way from the super- 

 ficial strata. 



' See, for instance, H. Mache u. St. Meyer: l^hys. Zeitschr. 6, 693. li)05; and H. W. Schmidt u. 

 K. Kurz: Phys. Zeitsclir. 7, 209. 1906. 

 - Proc. Roy. See. 77, 472. 1906. 



