234 



0. C. Lester — Emayiation Electroscopes. 



which varies with the pressure in exactly the same way as the 

 "constant" expressed in curies. The values of h for various 

 pressures may be taken from a curve easily derived from the 

 activity-pressure curves (ii^. 2) or better from the constant- 

 pressure curve (fit>;. 3). The latter curve and the 5-curve have 

 exactly the same form since the value of h is directly propor- 

 tional to the value of the " constant" at a given pressure. For 

 cliamber No. 2 the values of h at pressures of 40, 50, 60, 70 

 and 80 cm., are respectively 1-41, 1-166, 1-025, 0-949, and 

 0-905. On putting in the pressure factor equation (5) becomes 



I = 0-635 X IO- 



CS) 



This again must be multiplied by 1000 in calculating mache 

 units. Hence from the ionization current 



Mache units = 0-635 b 



771 



(7) 



But from the generally accepted relation between the mache 

 unit and the curie and from the calibration of the chamber 

 directly in curies we have 



77% 



Mache units = (2-7 X 10') X (curies) = 2-7 X 10' /^ — (8) 



Where k is the constant of the electroscope defined by equa- 

 tion (2). 



In Table lY are given a few results of the calculations in 

 mache units by both methods for chamber JSTo. 2. The data 

 given are based upon observations taken in the field. 



Table IV. 





Mache 



units 



Bar. Pr., cm. 



m 



V 



Kx 10-10 



b 



From eq. (7) 



From eq. (8) 



64 



7-965 

 40-60 



2-307 



0-989 

 1-025 



5-0 



4-97 



60 



2-39 



26-40 



26-20 



a 



5-58 



a 



u 



3-63 



3-60 



57-3 



5-245 



2-462 



1-0575 



3-64 



3-60 



54-35 



51-60 



2-557 



1-099 

 1-110 



36-0 



35-61 



53-6 



267-70 



2-583 



188-7 



186-7 



It will be noted that the values computed from equation (7) 



run slightly higher than those from equation (8). If we equate 



the two expressions for mache units writing x in place of 



2-7 X 10^ we get 



0-635 b 

 X = = — (9) 



