30 Velocity of Electrified Particles passing through Matter. 



in question takes the same form as the one found by Wilson. 

 From Wilson's Table II. (loc. cit. p. 147) we get 



for V = 2*8.10 10 , ^= -8-0.10- 6 . 



ax 



From the equation (3) on p. 19, we get for this velocity, and 

 using the same values for r and X log n s as above, 



^ = _8-8.10- 6 , 



ax 



a value which is in satisfactory agreement with Wilson's value. 

 The better agreement between theory and experiments for 

 fast /3-rays than for slower ones and for cathode rays is- 

 probably connected with the simpler experimental conditions 

 for the fast rays, for the latter keep their original uniformity 

 in velocity to a much higher degree in passing through 

 matter than is the case for the slower rays. 



Conclusions. 



In this paper the theory pf the decrease of velocity of 

 moving electrified particles in passing through matter is 

 given in a form, such that the rate of the decrease in the 

 velocity depends on the frequency of vibration of the electrons- 

 in the atoms of the absorbing material. 



It is shown that the absorption of a-rays in the lightest 

 elements can be calculated from the information about the 

 number and frequencies of the electrons in the atoms which 

 we get from the theory of dispersion, and that the values are 

 in good agreement with experiment. For elements of higher 

 atomic weight, it is shown that the number and frequencies 

 of the electrons which we must assume, according to the 

 theory, in order to explain the absorption of a-rays are of 

 the order of magnitude to be expected. 



It is further shown that the theory can account for the 

 form of the relations between the velocity of the rays and 

 the thickness of matter traversed, found by experiments with 

 cathode- and /3-rays. The absolute agreement as to tbe- 

 magnitude of the constants entering in the relations in 

 question, is very good for the fastest /3-rays, but not so good 

 for slower /3-rays and for cathode rays ; a fact which may 

 be due to the very difficult experimental conditions for these 

 latter rays. 



Adopting Prof. Rutherford's theory of the constitution of 

 atoms, it seems that it can be concluded with great certainty,. 



