770 Mr. A. L. Fletcher on the Radioactivity of 



obtained direct, unmistakable evidence that the act of ionization 

 of air molecules by both primary and secondary X rays of 

 widely varying degrees of hardness, as well as by and 7 rays, 

 uniformly consists, under all conditions which toe have been able 

 to investigate, in the detachment from a neutral molecule of one 

 single elementary electrical charge. 



Byerson Physical Laboratory, 



University of Chicago, 



February 14, 1911. 



XCI. The Radioactivity of some Igneous Rocks from Antarctic 



Regions. By Arnold L. Fletcher, B.A.I. , Research 



Assistant to the Professor of Geology in the University of 



Dublin*. 



HHHE question of the mean radioactivity of the Earth's 



JL surface materials is of sufficient importance, and at the 



same time so far from being definitely agreed upon, that 



experimental data tending to increase our knowledge of the 



subject seem deserving of record. 



The accompanying analyses of rock-specimens from the 

 Antarctic region of South Victorialand were determined upon 

 a series of rocks collected on the recent Expedition under 

 Lieutenant Shackleton, and kindly obtained and lent to me 

 by Professor Joly. They embrace rock-types of varied 

 chemical and petrographical characters. The determinations 

 were made by the solution method of Professor Strutt in 

 the manner described in a former communication. 



An examination of the constants of the two new electro- 

 scopes used was made by the standard uraninite solution 

 used in former experiments, and by a standard radium solu- 

 tion sent by Prof. Rutherford. It was found that two expe- 

 riments with Prof. Rutherford's solution on the constant of one 

 of the electroscopes read 0*63 and 0'62, and with Prof. Joly's 

 solution 0*61; and in the case of the other electroscope the 

 constant read 0*83 and 0*80 respectively with the two 

 solutions. The truth of the Uraninite Standard as used all 

 along in the calibration of the electroscopes is therefore 

 supported by these experiments. 



It is not without interest to note that on first comparing 

 these standards, that coming from Prof. Rutherford gave a 

 higher constant for the electroscopes referred to above, i. e. 1*1 

 and 1*7 respectively. This was traced to insufficient acidifi- 

 cation when diluting the standard solution sent. On adding 

 an additional quantity of HC1 and warming, the almost 

 perfect agreement recorded above was obtained. The con- 

 cealment of the emanation in the perfectly limpid solution 

 * Communicated bv the Author. 



