[CLINEj 



RADIATION AT THE SURFACE OF THE EARTH 



119 



mean were not greater than 1.5%, while in the other two they did not 

 exceed 3%. 



Further, the curves shown in Figs. II, III, IV, V, VI and VII 

 indicated, it will be seen, but little variation during the periods of taking 

 the readings. The readings from day to day, however, shewed con- 

 siderable variation but these were no doubt due to variations in the 

 amount of radioactive emanation present in the atmosphere. As the 



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Fig. 6. 



receiver was not hermetically sealed, the free interchange of air which 

 this condition permitted could easily account for the differences noted. 

 A point of interest in connection with these observations and one 

 which has been observed by other investigators was that the ionisation 

 was greater when the barometric pressure was low than when it was 

 high. A faUing barometer would promote the effusion of gases 





îïT^rcz 



Pig. 



occluded in the soil, and this process of effusion would consequently 

 result in an increase in the amount of emanation present in the air and 

 so account for the higher conductivity. 



