81 259 



through the tube /), about 1 ni. in length, out into the atmosphere. The cylinder k 

 is, as the illustration shows, placed in the middle of the vessel B. The whole was 

 arranged so that the gases evolved by the spring were spontaneously and without 

 supervision passed through the vessel in the manner described. The apparatus 

 thus arranged was left untouched for about 12 hours, when Ihe cylinder k was 

 brought to the tent, where its ionizing effect was measured in the ionisation cham- 

 ber. The rate of decay of the induced activity was then investigated. 



In these experiments the induced activity due to Ra-emanation was so predo- 

 minant, that I was not able in the time at my disposal, and with the apparatus I 

 used, to decide with certainty whether other kinds of emanation might nol be 

 present in the spring gases. 



If, therefore, the Icelandic spring gases contain thorium emanation or other 

 similar rapidly decaying emanations, they must be present only in very small 

 quantities in comparison with the radium emanation. In support of this view, I 

 will mention that we were unable to trace radio active substances in the sediments 

 or mud of any of the springs. For if the spring gases contained a large amount 

 of rapidly decaying emanations, one would reasonably expect to find in the spring 

 water the radio active substances responsible for these emanations, and therefore 

 also in the sediments and mud of the springs, and it is hardly possible that we 

 should have failed to detect them. 



The amount of radium emanation in the spring gases varied greatly in the 

 different groups of springs. The greatest amount of emanation in the gas samples 

 from Kerlingarfjöll, was about 43 times as large as in one of the gas samples at 

 Reykir, although the secondary exhalations from the lava fields of Bjarnarflagshraun 

 and Kjalhraun gave quite an insignificant amount of emanation compared with the 

 above-mentioned gas samples from Reykir. 



In springs belonging to the same group one also meets with considerable 

 variations in the amount of emanation, but these variations are, however, much 

 less than those between one spring group and another. We observe particularly 

 that when the springs in a group are similar in other respects, the variations in 

 emanation are also comparatively small. When, therefore, Boltwood' on the 

 occasion of his investigations of some hot springs in America states that the 

 amount of emanation in a spring cannot be deduced from the emanation in a 

 neighbouring spring, this only holds good, in the case of many Icelandic spring 

 groups, with regard to the smaller variations. As a rule, the amount of emanation 

 in the springs of a group is known approximately when one has determined the 

 amount of emanation in one of the springs. 



On the other hand, in the case of springs in the same group belonging to 

 dilTerent types, the variations in the emanation may be comparatively large. This 

 is the case with the hot springs at Hveravellir and at Reykjafoss. Acetous, sul- 



' Americ. Journ. Sc. 20, 128. 1905. 



1). K. 1). Vldensk. Selsk. Skr., 7. Hække, naturvidensU. oj! niiilhenl. Afd. VIII. 4. 34 



