160 Scientific Proceedings, Boj/al Dublin Societij. 



direction in the amount of emanation accumulating beneath tlie surface — a 

 result which might be anticipated. When rain chokes tlie soil, the amount 

 of emanation beneath begins to accumulate, as Grockel has pointed out. 

 The choking of the capillaries correspondingly reduces the amount of 

 emanation escaping at the surface. Hence wlien the one quantity is on the 

 increase, the other is on the decrease. We conclude, therefore, that fine 

 weather tends to diminish, and wet weatlier to increase, the richness of the 

 ground-gases. It is probable that after prolonged dry weather the amount 

 exhaled reaches a steady state. Further simultaneous expei'iments on the 

 amounts of emanation being exhaled and accumulating are desirable. It is 

 also desirable to investigate the rate of exhalation at various times in the day 

 and night. Our observations were in nearly all cases made in the forenoon. 



The most interesting feature of these experiments is the large amounts of 

 emanation which are found to escape from the surface of the soil. We have 

 already pointed out that the results obtained by several observers indicate an 

 amount of emanation in the atmosphere which, on average conditions, would 

 be in equilibrium with 80 X 10"'" gram radium per cubic metre ; and that 

 from this we must conclude that there must decay each hour the equivalent 

 of 2880x10-'° gram radium over each square metre of the land-surface, 

 assuming the radioactively homogeneous atmosphere to extend to a height 

 of 5 kilometres. This figure is frequently exceeded by our observations near 

 Milltown. It will remain for further experiments to show whether similar 

 high results are of common occun-ence. In the College Pai-k it is in no 

 case reached. It must be remembered, however, that not only is the 

 atmospheric content of radium emanation found to be very variable, but 

 we are by no means sure of our assumption that the atmosphere is radio- 

 actively homogeneous to a height of 5 kilometres. It appears as if the 

 foregoing observations support tlie conclusion that tlie gases u-liich eschale from the 

 soil are the chief and, pivbably, only considerable source of the emanation found 

 in the atmosphere. 



It is difficult to avoid the speculative conclusion tliat such large amounts 

 of emanation in the soils — and it must be remembered we have attended to 

 the emanation of radium only — exert an important influence on organic 

 activity. For instance, it seems probable tliat vegetable life is largely affected 

 by ionizing activities which have been shown to be capable of decomposing 

 carbon dioxide and other stable substances. Some experiments upon the 

 bearing on vegetable life of the soil-gases have been commenced. The subject 

 is attended with many difficulties, and it is too soon to report upon the results. 

 Since our experiments were commenced a paper has reached us recording 

 ;-esults obtained by Professor Ewart and Mr. Nightingall at Melbourne, on 



