﻿Ionization by Alpha Rays. 465 



was taken down. In all cases the positive current (i. e. that 

 with A positive) teas greater than the negative ; so that the 

 figures in the columns marked " dirT." have always the same 

 sign. 



5. It will be observed that the difference of the currents 

 in the two directions is never zero. Such a result is to be 

 expected, for the a rays give up their charge to B, and the 

 current due to this cause is not reversed when the field is 

 reversed. But part of the difference is due to Volta diL 

 ferences of potential in the measuring apparatus ; the mag- 

 nitude of this part was quite constant over long periods of 

 time, but was apt to change when alterations were made in 

 the apparatus. Measurements of its magnitude were made, 

 but they are unimportant for the present purpose. 



It will be observed that in Tables III. and IV., when the 

 electrodes are covered with the same material, the difference 

 between the currents is almost or quite constant for all values 

 of V. The difference may decrease slightly, which means 

 that the delta rays from B produce slightly less ionization 

 than those from A ; an effect of this nature may be attri- 

 buted to an absorption of the a, rays in passing between A 

 and B. But it may be confidently concluded (1) that the 

 apparatus is satisfactory in that ail the rays which emerge 

 from A strike B, and (2) that there is no difference to be 

 detected between the "emergence" and "incidence'* radia-. 

 tion of delta rays; for the rays from A are "emergent/' 

 those from B "incident." Any difference in the two forms 

 of radiation, which was indicated in the former experiments, 

 must be attributed, as was suggested before, to the many 

 sonrces of uncertainty to which the interpretation of the 

 measurements was liable, 



In Tables I. and II., however, the differences between the 

 currents change markedly when the potential difference is 

 increased. But this change cannot be attributed to a difference 

 in the ionization caused by the delta rays from gold and 

 aluminium, because it does not change its sign when the 

 position of those materials is reversed. In Table II. the 

 increase of the positive current relatively to the negative, if 

 attributed to a difference in the delta rays from the two 

 electrodes, would signify that more ionization is produced by 

 the delta rays from aluminium ; in Table II, it would signify 

 that more ionization is produced by the rays from gold. The 

 current flowing from A to B always increases relatively to 

 that flowing from B to A with whatever material the elec- 

 trodes are covered. The effect could bo attributed to some 

 geometrical asymmetry, were it not apparently dependent on 



Phil. Mag. S. 6. Vol. 23. No. 136. April 1912, 2 1 



