114 Prof. E. Rutherford on the Velocity and 



We see from the above tables that 



(1) The initial velocities of expulsion of the a particles 



from the products of the radioelements all lie between 

 1"56 X 10 9 and 2*25 X 10 9 cms. per second, i. e. the 

 maximum velocity of expulsion is only T14 times 

 the minimum velocity. Of all products, the a. par- 

 ticles emitted from thorium C have the greatest 

 velocity, and those from uranium and radium the 

 least velocity. 



(2) The average velocity and average energy of the 



a. particles from thorium and actinium families are 

 very nearly the same, and are greater than the corre- 

 sponding values for the radium family. The average 

 velocity of expulsion of the a particles from the 

 radium family (excluding radium F) is about 6 per 

 cent, less than that- of the a particles from thorium 

 and actinium e 



(3) The total energy liberated in consequence of the 



successive disintegrations of a radium atom is less 

 than the corresponding value for the thorium atom, 

 but is greater than that for actinium. 



Notwithstanding the smaller number of a. ray products in 

 thorium, the total energy liberated for the disintegration of 

 one atom of thorium is practically the same as the energy 

 liberated for an atom of uranium, including in the latter 

 radium as its product. 



Connexion of the velocity of expulsion of the a particle from 

 a product ivith the period of transformation. 



In considering the possibility of some relation existing 

 between the velocity of expulsion of the a particle and the 

 character of the transformation which accompanies it, it is 

 noteworthy that in a large proportion of the products, the 

 velocity of expulsion of the a particle for each of the radio- 

 active families increases progressively as the period of trans- 

 formation decreases. Since the period of transformation of 

 a product may be considered to be an inverse measure of the 

 stability of the atoms composing it, this would show that the 

 velocity of the expulsion of the particle is a function of 

 the stability of the atoms and is least for the most stable 

 atoms. 



This is well exemplified in the case of the products 

 uranium, radium, radium F, and radiothorium, which are 

 transformed slowly compared with the other a ray products. 

 The particles from uranium and radium have the minimum 



