by the Gamma Radiation from Radium. 395 



which is more than 60 per cent, higher than the mean of 

 the three above determinations. As no account of the ex- 

 periments of Moseley and Robinson has been published, up 

 to the time of writing this note, it is premature to make any 

 suggestions as to the explanation of the divergence of values, 

 but it seems surprising that there should be so large a 

 discrepancy for a constant which should surely be known 

 within a few per cent. 



The matter is of some importance inasmuch as the constant 

 K enters into the calculation of the ionization energy of the 

 y radiation, and the consequent heating effect due to y rays. 



Moreover, L. V. King* has used Moseley and Robinson's 

 value (N = 13xl0 14 ions, leading to K = 6 X 10 9 ) in his 

 estimate of the calculated diminution of the penetrating 

 radiation, due to radioactive matter in the earth, with in- 

 crease of altitude above the earth's surface. The diminution 

 with altitude as determined by Gockel and Hess f during 

 balloon flights is not in good agreement with the calculated 

 variation, but it is not suggested that the discrepancy has any- 

 thing to do with the value assigned to K. Hess has determined 

 the values of this constant for the testing vessels and Wulf 

 electrometers used in his balloon voyages, and the values 

 found for K, for the ionization within the vessels, are 

 5-67 xlO- 9 , and 4'87xl()- 9 . The materials of his testing 

 vessels do not appear to be stated in his paper, but assuming 

 them to be brass or copper or zinc, the corresponding values 

 for K in air J would be about 4 x 10 9 and 3*5 x 10 9 , which 

 are in fair agreement with my values. 



The writer has just made a fresh determination of K with 

 a thin cardboard testing vessel, lightly coated inside with 

 lamp-black, on a Wulf electrometer, and found K = 3"8 X 10 9 , 

 in good agreement with his three previous determinations. 



It is possible that the determinations of Moseley and 

 Robinson were made with radium emanation and active 

 deposit contained in a thin-walled glass vessel, and that 

 consequently their value of N(13 x 10 14 ) included the ions 

 produced by the softer radiations attributed to radium B§. 



It must be remembered that the values for K given above 

 by the writer do not include the ionization due to these 

 easily absorbed rays. 



For the purpose of calculation of the atmospheric ioniza- 

 tion, due to radium and its equilibrium products in the earth, 

 * Phil. Mag. October 1913. 

 t Pkys. Zeit. xiv. p. 614 (1913). 

 X Phil. Mag-. September 1912. 



§ Moseley & Robinson, Phil. Mag. xxiii. p. 312 (1912). Rutherford & 

 Richardson, Phil. Mag-. May 1913. ' 



