54 Prof. Thomson, On the positive electrification of a rays, etc. 



an important bearing on the determination of ejm for the a rays. 

 In these determinations it has been assumed that the a ray 

 retained its positive charge during the whole of its path under 

 the electric and magnetic forces, in the light of the above experi- 

 ments it seems by no means certain that this is the case. The 

 point could be tested by making experiments with different 

 lengths of paths ; if the a ray retains its charge, alteration in the 

 length of path would not affect ejm, if the ray lost its charge it 

 would. 



I wish to acknowledge my obligation to my assistant, Mr E. 

 Everett, for the help he has given me with these experiments. 



