0. C. Lester — Emanation Eleetroscopes. 



225 



Art. XYIII. — On the Calibration and the Constants of Emana- 

 tion E(eotroscoj)es ; by O. C, Lester. 



In the summer of 1914 the author began a fairly exhaustive 

 investigation of the radioactivity of the numerous mineral 

 springs found chiefly in the mountainous region of Colorado. 

 Most of the work was done in the held with instruments of the 

 usual types constructed in oar laboratory. However, owing to 

 certain peculiar conditions encountered in Colorado, it was 

 found necessary to make a careful study of the behavior of the 

 apparatus employed and to determine the significance of cer- 

 tain calibration constants. Further emphasis was given to this 

 study when it was found often practically impossible to com- 

 pare the work of different observers not only in different coun- 

 tries but even in the same country. This is particularly true 

 of the work of observers who express their results in terms of 

 the mache unit. Such a state of affairs ought not to exist in 

 any branch of science and an attempt is here made to point out 

 the reasons for the discrepancies, the remedy for which is 

 suggested by a study of the calibration constants and the cor- 

 rections which should be applied in the use of emanation elec- 

 troscopes. 



The emanation electroscopes used consisted of several ioniza- 

 tion chambers of different sizes, to each of which could be 

 attached the same electroscope head, including microscope, leaf, 

 and electrode. In general the apparatus is similar to that 

 described by S. C. Lind^ except that there is only one insula- 

 tion plug instead of two. Its essential features are shown in 

 fig. 1. I is an air-tight cylindrical brass ionization chamber 

 having stop cocks Y near the top and bottom. Altogether 

 four such chambers were used, all of them taking the same 

 electroscope head but each having its own electrode E. The 

 inside dimensions of the chambers and the outside dimensions 

 of their electrodes are given in the following table. The elec- 

 trodes are made of light brass tubing capped at each end. 



Table I. 





Length, cm. 



Diam,, cm. 



Electrodes 



I 



Length, cm. 



Diam., cm. 



No. 2 

 No. 3 

 Nos. 6 & 7 



24-8 

 25-1 

 21-2 



11-1 

 15-6 

 13-6 



19 



19-6 



13-1 



1-6 

 1-G 

 1-6 



* U. S. Bureau of Mines, Tech. Paper 88, Mineral Tech. 6, p. 17, 1915. 

 Am. Jour. Sci.— Fouuth Series, Vol. XLIV. No. 261.— September, 1917. 

 16 



