Earth' 8 Penetrating Radiation at Different Altitudes. 045 



the ionization began to increase when the receiver was about 

 14 or 15 metres from the wall. At the centre of the lawn 

 the reading was L5'l_, while at 13'7 metres from the wall it 



































Ions 











































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© 





























































X 



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V. 



































w— _ 



— © 





































14- 

































A7 e/rei 



was 15*4. At a distance of 10*7 metres the reading was 1G*4 

 ions per c.c. per second, and at 7*7 metres it was 16' 7. From 

 there on to the wall the readings remained practically steady. 

 As it had been shown previously that at any one place 

 readings could be taken with the apparatus which did not 

 show a variation greater than 3 per cent., it is clear from the 

 numbers given above that the wall emitted a radiation whose 

 range extended out in the air from the wall to a distance of 

 between 14 and 15 metres. The absorbing power of this 

 amount of air is roughly equivalent to between 6'5 and 

 7 millimetres of aluminium, nnd this thickness, it has been 

 pointed out, is practically what Pound * found necessary to 

 cut off all the radiations of the /3 type issuing from a sample 

 of radium in equilibrium. 



It follows then that the wall emitted a radiation of the ft 

 type which produced a conductivity in the air in the zinc 

 receiver corresponding to about 1*5 ions per c.c. per second. 



From the nature of the observations it is impossible to 

 determine whether this radiation was emitted directly by the 

 wall or was a secondary radiation produced at the wall by the 

 penetrating rays present at the surface of the earth. In 

 either case it seems justifiable to conclude that a similar 

 radiation was probably emitted by the soil of the lawn and 

 contributed to the ionization obtained in the receiver when 



* Pound, loc. tit. 

 Phil. Mag. S. 6. Vol. 22. No. 130. Oct. 1911, 



2 U 



