Joi.Y AND Smyth — Amount of Hadium Emanation in the Soil. 157 



In tliis manner the observations given in Table IV were carried out in 

 the College grounds at a point close to the outer wall of the Laboratory on 

 the east side and in grass. The area covered by the collector being just about 

 one twenty-fiftii part of a square metre, the amount of emanation in the eleeti o- 

 seope multiplied by 25 is entered in the second column as the amount of 

 emanation escaping per square meti'e per hour. 



'J'abi.e IV. 



E.ri)erimentt; on tlie Extnildfioii of Rddiuiii Emanation in tlie Grounds 



of Triniti) College. 



It was thought desirable to make similar observations at Somerset House. 

 The observations were partly in grass, partly in open soil, at a pouit adjoin- 

 ing the tennis-court. It will be seen that these results are in keeping with 

 those on the ground-gases. In these experiments the rate of flow of the air- 

 draught through the collector was not very different from that used generally 

 in the experiments recorded above, the amount of negative pressure at a point 

 between the charcoal tube and the water-pump being sensibly the same in both 

 eases ; that is, it was found to be such as would balance a head of from 10 to 

 20 cms. of water. The pump was always run with this gauge in operation, 

 both in the ease of the experiments made in College and those made at 

 Somerset House. The exact measure of the air-flow in the case of the former 

 experiments was ascertained by finding the time required for a certain volume 

 of air contained in an indiarubber bag to be withdrawn by the pump. 



2 a2 



