a Particles from Thorium Active Deposit. 709 



The mean value of the ratios 



p x : p 2 : p z h 1 : 0*932 : 0-832. 



If we compare the values of the velocities as tabulated by 

 Rutherford and Robinson we get 



Vl : v 2 : v 3 :: 1 : 0*932 : 0*826. 



We may thus conclude that the value of the velocity (i\) of 

 the a-particles of range S'6 cm. given in the table is correct, 

 assuming the accuracy of the velocity for radium C, whilst 

 the value given for the velocity of a-particles of range 

 4*8 cm. is slightly low, i. e. the range 4*8 cm. is a little too 

 small. Assuming the correct ranges of the a-particles from 

 ThC 2 and RaC to be 8*60 cm. and 6*94 cm. respectively, 

 and using the value of the ratio of the velocities 0*832 

 obtained in the present experiments, we deduce from Geiger's 

 relation that the range of the a-particles from thorium C is 

 4*95 cm. 



Taking the velocity 1*922 x 10 9 cm. per sec. as the velocity 

 of the a-particles from radium C we obtain, as the mean of 

 all observations 



(a) Velocity of a-particles (of range 8*6 cm.) emitted 



from thorium C 2 , 



= 2'060 xl0 9 cm./sec. 



(b) Velocity of a-particles (of range 4*8 cm.) emitted 



from thorium Ci, 



= 1*714 xl0 9 cm./sec. 



Summary of Results. 



(1) By measuring their relative deflexions in a magnetic 

 field, an accurate comparison has been made, by the photo- 

 graphic method, between the velocities of the two groups of 

 a-particles (ranges 4*8 cm. and S'6 cm.) expelled from 

 thorium active deposit. 



(2) The mean value of the ratio of these velocities is 

 found to be 1 : 0*832, whereas the value calculated from 

 Geiger's relation (v 3 = kR) gives 1 : 0*826. To explain this 

 difference it is suggested that the value 4*8 cm., previously 

 accepted as the range of a-particles from thorium C, should 

 be increased to 4*95 cm. 



