158 



Seientific Proceedings, Royal Dublin Society. 



Taki.e VI. - 



&2}erimeiits on the Exhalation of Emanation of Radium in the Groundu 



of Somerset House. 



The first four of these results were obtained when the collector was on 

 grass ; the remainder wlien it stood on open, compact soil. 



Throughout these exhalation experiments there is a source of error which 

 has to be considered. The air drawn tlirough the charcoal tube is derived 

 from the atmosphere, and accordingly contains the amount of emanation pre- 

 vailing at the time. It is easy to see that the error is small. The average 

 rate of the air-current involves the passage through the charcoal of about 15 

 litres in the hour. This will be found to involve a correction on the figures 

 tabulated of about 30 x 1 0"^-. As doubtless other sources of uncertainty of more 

 considerable magnitude prevail, and as it is probable that the method on the 

 whole underestimates the escape of emanation uuder normal conditions, we 

 have not made this correction. 



The results now given can best be studied by plotting them on loga- 

 rithmic paper. As there is a certain relation between the several series of 

 experiments, all are plotted upon the one sheet. There are some points of 

 special interest. 



The results for ground-gases from a depth of 25 cms. selected from 

 Table I are seen to rise from a relatively low to a high value. The explana- 



