258 



80 



particular causes had not been at work to keep the bulk of the lava hot. Bearing 

 in mind that there are hot springs in the immediate neighbourhood of the atmos- 

 pheric exhalations both in Bjarnarflagshraun and in Kjalhraun, it is very probable 

 that the high temperature of the lava is maintained by heat conduction from hot 

 springs beneath the lava. They have not been able to break through the hard 

 crust at the bottom of the lava, but have been compelled to find an outlet at the 

 edge of the lava field. The atmospheric exhalations may therefore be correctly 

 characterized as secondary hot springs, as distinct from the real hot springs, in 

 that they derive their heat energy from the latter. 



The exhalations from the above-mentioned secondai-y hot springs contained 

 very little radio active emanation. It was therefore out of the question to deter- 

 mine the character of the emanation. But the ionizing effect of the radio active 

 emanations from the other hot springs was so great as to render this possible. As 

 to the methods employed, I refer to page 35. The investigations showed that the 

 ionisation in the ionisation chamber increased immediately after the introduction 

 of the spring gases, in such a way as might be expected if the gases contained 

 no other emanations than radium emanation. 



The coefficient of transformation calculated from the experiment, and referred 

 to in Table I under the head of a is of the same magnitude as the coefficient 

 of transformation for radium emanation (2.16 x 10 ") found by Rutherford. The 

 divergences seldom exceeded probable experimental errors, the latter of course being 

 rather great owing to the difficult conditions under which the experiments were 

 carried out. 



Taken as a whole, the divergences of a for spring gases from the same group 

 appear to be to some extent of a systematic nature, in that a for the same group 

 is generally either too great or too small. Blit bearing in mind that the ionisation 

 in the ionisation chamber apparently made the same progress whether the spring 

 gas was examined immediately after the gas was collected, or after it had stood 

 three or four days in the collecting bottles before it was investigated for radio- 

 activity, it seems rather improbable that these small divergences, even though they 

 are systematic, should be due to different radio active emanations. They are more 

 likely to be due to small systematic errors in the treatment 

 and investigation of the gases. The Icelandic spring gases may 

 therefore for the present be regarded as not containing any 

 slowly decaying radio active emanation except radium emanation. 

 Rapidly changing radio active emanations such as, for 

 instance, thorium and actinium emanation, cannot of course 

 be examined in the same way. I therefore endeavoured to 

 examine them in the following manner. 



The spring gases were conducted from the collecting funnel, 

 which was placed in the spring, through the tube a (Fig. 16) 

 into the tin vessel B. From B the spring gases were passed 

 Fig. 16. 



