Emanation in the Lower Regions of the Atmosphere. I: 



charcoal behind to absorb the emanation. Experiments, 

 however, were made to test whether the amount of emanation 

 absorbed depended upon the dryness or wetness of the air, 

 and it was found to be practically independent of the amount 

 of moisture present. 



In the present series of experiments to measure the amount of 

 emanation in the air, two silica tubes each containing the same 

 amount of charcoal were used, and they were laid side by 

 side upon the bench. The left-hand end of each tube was 

 joined to the side-arms of a T-piece (see fig. 2), the leg of 



Fig. 2. 



JIL 



3-* 



the T communicating by a long glass tube to the outer air, 

 its extremity being about 6 feet above the ground. The 

 right-hand ends of the tubes were joined to gauges which 

 measured the air-stream, and these communicated with a large 

 bottle from which a pipe led to the water-pump. During the 

 experiments, air-streams of the same magnitude (half a litre 

 per minute) were drawn through the two tubes ; so that if 

 the charcoal in the tubes is in the same condition as regards 

 size of particles and packing, the tubes ought to absorb and 

 consequently to yield when heated the same amount of 

 emanation. Usually, as will be seen from the tables 

 (pp. .10-17), the amounts were very nearly equal ; but in a 

 few cases there were unaccountable discrepancies between 

 them. At any rate one tube served as a check on the other. 



The tubes having been first cleared of emanation by heating 

 to a red heat and drawing air through them between 2 and 

 4 p.m^ were connected up as described above, and the air- 

 stream started at about 5 p.m. After an hour's reading of 

 gauges and regulating of clips the air-streams were obtained 

 steady at half a litre per minute, and the tubes were left for 

 the night. At about 8 A.M. next morning the gauges were 

 read ; and if there had been any wandering away from the 

 mark the air-streams were again adjusted to half a litre per 

 minute. Just about 2 p.m. the gauges were again read and the 

 air-stream stopped. The exposure had thus lasted for about 21 

 hours, and about 630 litres of air had passed through each tube. 



The tubes were then heated in turn, and the emanation was 

 tested as described above. The heating and testing took 

 from 2-6 P.M., but the tubes were cold by 5 P.M., and they 

 were then reconnected up and the air-stream set running for 



