Velocities of a Particles from Radioactive Substances. 569 



once deduced from the relation found by Geiger, viz. v ? =KE, 

 where R is the range of the a particle in air. The results 

 are included in the following table : — 



! 



Substance.' 



Range of a ray 



in air at 15° C. 



and 76 cm. 



Velocity in 

 cm./sec. 



mv | electromag- | 

 "jf \ netic units -1 J 



nv 2 energy 

 E e 



= Arrange. 



U*i 



Ur 2; 



Ionium 



Ra 



Ra Em 



RaA 



2-50 cm. 

 2-90 ., 

 300 „ 

 3-30 „ 

 4-16 „ 

 4*75 „ 

 6-94 ., 

 3-77 „ 



1-37x10° 

 1-44 „ 

 145 „ 

 1-50 „ 

 162 „ 

 1-69 „ 

 1-92 „ 

 1-57 „ 



1-41 xl0 ,J 

 T58 „ 

 1-64 „ 

 T72 „ 

 1'80 „ 

 1-70 „ 

 206 ,. 



2-84x10? 

 298 „ 

 301 „ 

 3-11 „ 

 3-36 „ 

 3-51 „ 



3-88 Xl0 u 

 4-28 „ 

 4-38 „ 

 4-67 ., 

 5-44 „ 

 5-95 .. 



RaC ... 



RaF 



3-985 „ | 7-66 „ 

 3-25 ., i 5-10 „ 







Th 



Radio Tli ... 

 ThX 



2-72 cm. 

 3-87 „ 

 4-30 „ 

 500 „ 

 570 „ 

 4-80 „ 

 8-60 ., 



2-92 xlO 5 

 3-28 „ 

 3-40 „ 

 357 „ 

 373 „ 

 352 „ 

 4-28 „ 



410 Xl0 u | 

 519 „ 



5-57 ., 



| Th Em 



Th A ... . 



6-16 „ 

 6-72 „ 

 5-99 „ 



8-84 „ 



ThC^ 



ThC 2 



Radio Act... 460 cm. 



ActX 4-40 ., 



Act Em ... 570 „ 



Act A 6-50 „ 



1 Act C 5-40 „ 



1-68x10* 

 1-65 „ 

 180 „ 



1-88 ., 

 1-77 „ 



3-48 x 105 

 3-42 „ 

 373 „ 

 3-90 ,, 

 366 „ 



5-82 X 10 u 

 5-65 „ 

 6-72 „ 

 7-33 „ 

 6-48 „ 



Heating effect of the a. particles from radium. 



It is of interest to calculate from the present data the 

 total energy associated with the a particles expelled per 

 second from one gram of radium and its products, and to 

 compare it with the observed emission of energy in the form 

 of heat. 



The rate of emission of energy in the form of a rays is 

 ^ 2 nmv 2 , where n is the number of a particles emitted per 

 second from each product, and v the velocity. Since in 

 equilibrium, the same number of a particles is emitted from 

 each product per second, 



1 V 2 1 T? ^ mi ' 2 • 



\ 2, nmc~ = pihi 2, ^r 



for each product is obtained from the 



mvr 



The value 

 above table. 



The value of 11E = 10*54 x 10" 10 e.m. units was found 

 directly by Rutherford and Geiger by measuring the charge 

 carried by the a particles. The number so obtained has 



