Velocity of Swiftly Moving Electrified Particles. 601 



recently been very limited on account of the great difficulties 

 in the measurements. Much light, however, is brought upon 

 this question by the study of the homogeneous groups of ft 

 rays emitted from certain radioactive substances. 0. v. 

 Baeyer* observed that the lines in the " ft ray spectrum/' 

 produced when the rays are bent in a magnetic held, were 

 shifted to the side of smaller velocities when the radioactive 

 source was covered by a thin metal foil. The question has 

 recently been more closely investigated by Danyszf, who 

 •extended the investigation to a great number of the groups 

 of homogeneous rays emitted from radium B and 0. The 

 first two columns in the table below headed by Hpand A(Hp) 

 contain the values given by Danysz for the product of the 

 magnetic force H and the radius of curvature p lor a number 

 of groups of homogeneous ft rays, and the corresponding 

 values for the alteration in this product observed when the 

 rays have passed through an aluminium sheet of 01 gr. 

 per cm. 2 The limit of error in the values for A(Hp) is 

 stated to be about 15 per cent. 



Hp. 



A(Hp). 



0. 



/3 3 A(H f ,). 



1391 



124 



0-635 



31 



1681 



95 



0704 



33 



L748 



90 



0-7)8 



33 



1918 



66 



0750 



28 



1983 



61 



700 



27 



2047 



i>i\ 



0-770 



26 



2224 



57 



0-795 



28 



2275 



48 



0-802 



25 



2939 



37 



0-8G7 



24 



3227 



48 



0-885 



33 



4789 



39 



0-942 



32 



5830 



32 



0-960 



28 



The values for Hp are connected with the velocity of the 

 ft particles through the equation 



-H= rra 



■('-?)• 



deduced on the expression for the momentum of an electron 

 which follows from the theory of relativity. Denoting V/c 

 by ft, we get 



* Phy$, Zettsehr. xiii. y. 485 (1912). 

 t Journ. de Phyaique } iii. ; . 941) 1913). 



(U) 



