the a Particles of Radii 



337 



These results are shown graphically in fig. 3, in which 

 the ordinates and abscissae represent the numbers in the first 













Fig 



3. 

























/tor 



-A 











T" 













/ 

 / 





£C 



h 







*? 













4 



6?t-x 



/ 



x-C 4 



H,o° 









5 









/ 



/ 



' / 



\ c 





















Cu 



/ 





W 7 Br 



ff 3 t 



CI 













c 





M* 



, / 











































+■ ■ 



/ / 



s 





















s 





i 





p 



4- 





3 





4 









and second columns respectively. It is curious that the 

 metals and gases seem to lie on rather different lines. Pos- 

 sibly this is due to the difference between solid and gas; 

 possibly again to the fact that the gases tested have such 

 complex molecules. Further research may make the point 

 clearer. Several other points arose in the course o£ the 

 experiments, which deserve further inquiry. For instance, 

 the metal films did not cause exactly the same drop through- 

 out all the curve ; the slower a particles were a little less 

 affected than the swifter. 



§iv, 



From these results it appears that the following law is 

 true for certain elements, at least to a first approximation. 



The energy spent by an a particle in its passage through 

 an atom is proportional to the square root of the atomic 

 weight. It can never be said that this is a law which is 

 general to all the elements until all the elements have been 

 experimented upon. In the case of many of them, the ex- 

 perimental difficulties will be very great. Since, however, 

 the law holds with some accuracy in several cases, it becomes 

 desirable to consider whether any physical interpretation can 

 be placed upon it. 



