JoLY AND Smyth — Amount of Radium Emmuition in the Soil. 159 



tioii is that the earlier observations were made at the conohisiou of a long 

 period of drought, during which the escape of gases from the soil had been 

 unimpeded by free moisture choking tlie capillaries. A period of rainy 

 weather then set in, and the emanation began to accumulate. Near the 

 beginning of May fair, dry weather again set in, when the radioactivity of 

 tlie ground-gases began to decline, and continued to fall throughout the 

 earlier part of the long spell of fine weather which succeeded. The experi- 

 ments ceased on May 17th. Careful comparison with tlie barometric curves 

 of the period covered by the experiments shows no direct influence of 

 changing pressure upon the readings. 



The results obtained from depths of 100 cms. show what appears to be a 

 lag on tliose from tlie lesser depth — just such a lag as changes of temperature 

 arising from diurnal or seasonal changes at the surface would show. The 

 points of minimum and maximum emanation richness are at a later date 

 than those observed at the depth of 25 cms. Followed up to June 7th they 

 show that a rapid rate of loss of emanation was prevailing, even at this 

 depth, during the phenomenal drought of May and June this year. 



When, lastly, we select the observations referring to a depth of 150 cms., 

 we see indications of a still greater lag behind those of 25 cms. The 

 recovery from the initial depression seems displaced about ten days later, 

 and the partial depression of May 1st also to ten days later. The readings, 

 as might be expected, showed on the whole a less degree of fluctuation. 



The readings at Milltown were only commenced when the fine weather 

 was just coming in. The absolute values of the readings are so high that 

 they have to be plotted to one-tenth the scale of those taken in Trinity 

 College. They agree in their tendency with those at a similar depth in the 

 city. 



Mr. A. L. Fletcher was so kind as to make a determination of the radium 

 content of the soils in the College Park and at Somerset House. As it is 

 only the finer constituents which can supply any large amount of emanation 

 to tlie ground-gases, the material examined was obtained by sifting from 

 the soils tlie finer particles. A mesh of 60 to the inch was used. The 

 powders so obtained were treated in the electric furnace by the fusion 

 method. The radium content of the fine constituents from the College Park 

 was found to be 2-8 gram per gram ; that from Somerset House 5-2 gram 

 per gram. Tlie quantity of the finer constituents in the two soils was 

 46 per cent, and 56 per cent, respectively. 



Coming now to the exhalation experiments in Trinity College, the 

 interesting fact appears that progressive variations in the amount of emana- 

 tion exhaled from the soil are attended by progressive changes in the other 



