0. C. Lester — Emanation Electroscopes. 235 



If we now substitute correspond in o^ values of 1> and k from 

 the above table and compute the several values of x we find 

 that they agree closely and give as a mean value 



X = 2-726 X 10' (10) 



which is the relation between the mache unit and the curie 

 necessary for exact agreement between the results by the two 

 methods if we assume that the saturation ionization current is 

 accurately determined by the constarts found and the correc- 

 tions applied. This value is about half way between the theo- 

 retical value 2*75 X 10' sometimes used and the value 2-7 X 10" 

 usually taken. 



To be exact, 2*75 X 10' gives the theoretical relation between 

 the mache unit and the curie on the Rutherford-Boltwood 

 standard. According to Rutherford* it is 2*89 X 10' on the 

 International Standard and Mache and St. Meyerf give it as 

 2*67 X 10' on the Vienna Standard. Of course this relation is 

 nothing but the saturation ionization current due to one curie 

 of emanation without disintegration products, multiplied by a 

 thousand. 



Among investigations in the radioactivity of mineral springs, 

 and in particular among those on European mineral springs, 

 there can be found often the results of several observers on the 

 same water or gas. It is rarely that these results agree 

 closely and those of one observer may range anywhere from 

 many times to a fraction of those given by another. With 

 precautions field work can be made practically as accurate as 

 that done in the laboratory. Hence discrepancies in the work 

 of equally careful observers have often been attributed to varia- 

 tions in the activity of the source. On the other hand, there 

 are springs which have shown no appreciable variation in 

 activity when examined systematically at different times of the 

 year by the same observer using the same apparatus. Undoubt- 

 edly some springs do vary in activity but the question of their 

 variability and even the amount of their activity can scarcely 

 be determined from the work of different observers so long as 

 there is no uniformity in standards, in methods, and in the 

 nature and the number of the corrections to be applied to the 

 observations. This is particularly true of results expressed in 

 mache units based upon ionization currents. In many cases 

 mache units are apparently calculated from the observed ioni- 

 zation current and not from the saturation ionization current 

 when all radiation is absorbed in the air of the chamber. In 

 the first case the mache unit is dependent upon the dimensions 

 of the jDarticular apparatus used and upon the potential applied 



*Phil. Mag. (6), vol. xxviii, p. 330, 1914. 

 f Phys. Zeitschr, loc. cit. 



