0. C. Lester — Emanation Electrosco])es. 233 



the air in them, and the difference of potential between the 

 electrodes and walls that there was neither opportunity for the 

 production of all the ions possible nor a sufficiently strono- elec- 

 tric Held to remove all those that were produced. This makes 

 no difference for measurements in curies^ if the chambers have 

 been properly calibrated. However, it is possible from the 

 work of Duanef and of Dnane and Laborde;}: to calculate for 

 such chambers as were used the relation between the maximum 

 ionization current actually observed and the number of curies 

 which would produce it if the radiations had been completely 

 absorbed and saturation had obtained. >J In this way it was 

 found that the loss, due to lack of raiige and saturation, in the 

 ionization current upon which the mache unit is based, amounted 

 to 4S per cent in chamber No. 2, to 46-7 per cent in chamber 

 No. 3, and to -1-tl: per cent in chambers No. 6 and 7. Hence in 

 all the chambers used except No. 2 it happens that the loss in 

 activity due to the above-mentioned causes is almost exactly 

 counterbalanced by that added by the active deposit. 



The ionization current in electrostatic units is given by 



i ^ gem 



300^ (3) 



where g is the drop in potential in volts per scale division, m 

 is the number of scale divisions passed over by the leaf in t 

 seconds, and c is the electrical capacity of the instrument. In 

 the case of chamber No. 2, q = 1-22, C = 8*4:, and if 7n is the 

 number of divisions per minute passed over by the leaf at 

 maximum activity due to emanation from v liters of water or 

 gas (3j becomes 



. ^ (l-22)(8-4) m ^ ^..333 ^^^3 jn KSJL ^.^ 



(30u)(6U; • V V hter 



^hen corrected by Duane's factor for the absorption due to 

 the walls of the vessel and for the activity due to the decay 

 products according to the percentages given above (-1) becomes 



I = 0-635 10-' — (5) 



V 



where I denotes the total ionization current which could be 

 produced by the emanation alone if all its radiation was 

 absorbed in air. 



Equation (5) holds for a barometric pressure c»f 62-5''^ only 

 and the observed values of m must be corrected by a factor b 



* W. E. Barss, this Journal, vol. xxxiii, p. 546, 1912. 



f Log. cit. | Loc. cit. 



^G. Berndt, Ann. der Phys. (4), vol. xxxviii. p. 958, 1912. See also 

 Gockel, loc. cit.. Chap. VIII, and H. Mache and St. Meyer Phys. Zeitschr., 

 vol. xiii, p. 320, 1912. 



