﻿Ahsorption and Scattering of the u Rays. 907 



and call k the parameter of the curve. It depends on a and 

 V and is taken in this form to facilitate the use of logarithms. 

 The functions E 1? E 2 were evaluated by quadrature. The 

 velocity curve obtained from E x is shown : 



in the figure for 























































4^ 







^ 







^u 



$• 



























f^T" 

































































































































































<a 







































\ 











































■\ 













































































\ 





V 











































\ 









0-3 0-6 0-9 1-2 1-5 1-8 



<D/ST/)NCE. 



To avoid confusion each curve has been started 03 from the last. 



parameters 1,2, 3, 5. Those for E 2 are almost indistinguish- 

 able on the scale of the drawing. The curve for k = 3 is within 

 ■J per cent, of the curve ?/ 3 = l — '99a 1 from x = to a? = '95, 

 which is well within the experimental errors. Ihat for /c = 2 

 is nearly as good but diverges rather more at the end. For 

 parameters greater than 2 it will be seen that the curve of 

 velocity falls very steeply near #==1, and this corresponds to 

 the existence of a range, which is so important a feature 

 of the motion of the a rays. As the velocity diminishes 

 there comes a point of inflexion and the final loss of 

 velocity is exponential. Actually this part probably does 

 not exist, as the a particles, which are straggling consider- 

 ably, will undergo large deviations frequently, and it is very 

 likely will pick up charges and become common gas mole- 

 cules. 



Equation (6) is thus capable of qualitatively representing 

 the motion of the a rays. A great danger of basing a theory 

 to account for experiments on a given law of force of the 

 elementary parts, is that the supposed mechanism should not 

 be the only one capable of accounting for the phenomena. 

 This has caused trouble in such matters as viscosity, surface 

 tension, etc. It would be hard, in the present case, to show 

 that no other law of force could produce the same velocity 

 curve, but that the curve cannot be obtained by merely sup- 

 posing the a particles to surge through the atom with any 



