Emanation from the Soil to the Atmosphere. 635 



Experiments were attempted with a view of getting some 

 idea of the variation of emanation outflow from hour to hour. 

 The current of air from the collector was led directly through 

 an electroscope, and the rate of discharge observed con- 

 tinuously. The length of tube (45 feet) connecting the 

 collector with the electroscope, and the slow rate of air-flow 

 necessary in order that the draught might not disturb the 

 gold-leaf, ensured the decay of thorium emanation before 

 reaching the electroscope. 



Before attaching the end of the suction-tube to the col- 

 lector, the former was supported about 5 ft. above the surface 

 of the soil, so that a current of atmospheric air flowed through 

 the electroscope for a few hours. The rate of discharge was 

 observed during this time. The tube was then attached to 

 the collector, and the rate of discharge read again during 

 some hours. 



It was found that, in most cases, the emanation was too 

 dilute to produce any appreciable effect on the rate of dis- 

 charge. The following three experiments, however, gave 

 results : — 



1912. 



12 Jan. ... 



14 Jan. ... 



2 May... 



Eate of discharge in scale-divisions per hour. 



Before attaching collector. 



After attaching collector. 



Length of time observed. 



Rate. 



1st hour. 



2nd hour. 



3rd hour. 



\\ hours 



50 mins. 



2 hours 



5-3 



6-1 

 50 



12-4 

 9-4 

 6-6 



8-7 

 100 



7-5 



8-4 

 8-6 



These meagre results at least show that there may be 

 considerable differences from hour to hour in the amount of 

 emanation escaping from the soil, and that too much signi- 

 ficance must not be attached to the details of the exhalation 

 curve. 



We may, I think, conclude from a study of the curves 

 that there is no seasonal factor involved. 



The condition which seems to have the most distinct effect 

 is wind strength. A strong wind is very frequently accom- 

 panied by an increase in the amount of emanation escaping 

 and a diminution in the amount registered below the surface. 

 This phenomenon may be traced on the following dates (see 

 curves) : Aug. 24-26, Sept. 1, 23, Oct. 21, Nov. 6, 14, 30, 



