Danysz and Duane — Electric Charges of a- and $ Rays. 301 



indicating that the /3-rays do not produce secondary rays of 

 small velocity. 



The above results are similar to and confirm results obtained 

 several years ago* in experiments on the secondary rays due to 

 the a-rays from radium itself and from radium C. 



The curves in figure 3 indicate an increase in the current, 

 starting from field strengths of about 115 gauss, until a maxi- 

 mum value is reached in the neighborhood of 3000 gauss. 

 The increase is due to the progressive suppression of the /3-rays 

 by the magnetic field, and the maximum represents the charge 

 carried by the a-rays alone. 



The smallest velocity of the /3-rays may be estimated by the 

 formula of Lorentz 



mw ix 



Hr = " 



where /x is the ratio of the velocity v of the /3-particle to the 

 velocity w of light. We have seen above that a ray will not be 

 stopped by the field, if the radius of curvature of its path is 

 greater than 10 cm ; and since a field of 115 gauss begins to stop 

 the /3-rays, the value of B> for the slowest of them is 1150, 

 corresponding to a velocity of about 1*7 X 10 10 . This value is of 

 the same order of magnitude as that (1*85 XlO 10 ) of the slowest 

 beams of rays previously observed coming from a thin -walled 

 glass tube containing' radium emanation, f and we conclude 

 that there are no /3-rays from our source stopped by fields 

 smaller than that corresponding to the minimum of curve 1 

 (figure 3). 



On account of the flatness of the curves the maximum 

 velocity of the /3-rays is difficult to estimate. Those that are 

 just suppressed by a field of 2500 gauss have a velocity of 

 about 98 per cent of that of light, and 5000 gauss is sufficient 

 to stop the fastest /3-rays the velocity of which has been 

 measured. 



We assume, therefore, that the current observed with a field 

 of 8000 gauss corresponds to the charge carried by the a-rays 

 alone, and that the minimum corresponds to the a-ray charge 

 diminished by that of all the /3-rays capable of penetrating the 

 glass of these thin spheres. 



Messrs. Hahn and v. Baeyer and Miss Meitner have observed 

 a few rays slower than the above, which they attribute to 

 radium B. These rays, however, probably do not get out of 

 the little sphere and are not measured in these experiments. 



* Duane : Science, xxiv, 48, 49, 1906 ; Le Radium, February, 1908 ; 

 Comptes rendus, July, 1908. 

 •{■Danysz, Le Kadiuin, 1911. 



Am. Jour. Sci.— Fourth Series, Vol. XXXV, No. 207.— March, 1913. 

 21 



