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BELL SYSTEM TECHNICAL JOURNAL 



of sixteen kilometres, in air at standard pressure, is of the order of 

 200 ions per cc. per second! This is considerably greater than the 

 modest value of 1.5 prevailing at the level of the ground. 



I must make at least a passing allusion to the fluctuations of the 

 intensity of the cosmic rays — fluctuations which are smoothed over 

 by some of the experiments and missed by others, for they are too 

 small to be certainly detected by measurements of low precision, and 

 many are too rapid to be noticed by measurements on the amount of 

 discharge of an electroscope over a period so long as one or two hours. 



I0°( 

 770 1 



12 18 6 12 18 6 12 18 6 12 16 6 12 18 6 12 18 6 12 16 6 12 16 



TIME *-■ 



Fig. 9 — Fluctuations of cosmic-ray intensity and attendant fluctuations of barometric 

 pressure and temperature (Hoffmann). 



4.17 ±0.09 



4.0 — 



-5.10 + 0.14 

 -5.0 



Fig. 10 — Fluctuations of cosmic-ray intensity observed at high altitude in the Alps 



(von Salis). 



Figs. 9 and 10 display examples of these: to appreciate the ratio of 

 their average amount to the mean value of the ionization, one must 

 take note of the scale of ordinates on the left. The former is especially 

 instructive, for both the uppermost and the lowermost of the curves 

 display the ionization of the air near the ground (in a basement at 



