Experiments on Delta Rays. 529 



given potential difference) was changed. The electrodes 

 were covered with aluminium, and the distance between 

 them could be altered in the ratio of 1 to 2 '5 (apprcx.) 

 without violating the necessary geometrical conditions. The 

 following table shows that the relation between current and 

 potential difference is independent of the field strength, and 

 that, when the electrodes are of aluminium, the form of the 



Table I. 



P.D. 



Current. 



Electrodes 05 era. apart. 



Electrodes- 12 cm 



apart. 



10 



1000 

 •987 

 •968 

 •948 

 •926 

 •889 

 •839 

 •755 

 •634 

 •412 

 



1-000 

 •985 

 •968 

 •950 

 •927 

 •889 

 •837 

 •759 

 •643 

 •423 

 





9 



8 



7 



6 



5 



4 



3 



2 



1 









relation is determined by the velocity of the rays. It is not 

 proved that, in this case, the " simple theory " of that rela-? 

 tion, given in the first p;iper, is adequate, for the possibility 

 of a reflexion of the rays, which depends upon the velocity, 

 has to be taken into account Nevertheless, these two exr 

 periments do much to remove the uncertainties which were 

 previously attached to interpretations of the experiments 

 based on that theory ; it appears that some small proportion 

 of the rays, at least, must have an initial velocity as great as 

 10 volts . 



4. It was concluded from the previous work that the 

 relation between current and potential difference, and there- 

 fore the distribution of the initial velocities of the rays, 

 was independent of the velocity of the exciting alpha rays. 

 The velocity of the exciting rays had been varied only by 

 inserting absorbing layers in the path of the rays from 

 polonium. A variation over a wider range was now ohr 

 tained by substituting for the polonium the active deposit 

 of thorium obtained from a preparation of mesothorium. 

 The range of the polonium rays is 3'9 cm., that of the rays 

 from ThB and ThP 5*0 and 8*6 cm. The experiments 



