248 On Rays of Posit ice Electricity. 



one unit ; the attraction, however, between A and B due to 



their electric charges has been increased, so that the system 

 AB is less likely to break up into atoms than it was before 

 the collision took place. Suppose, however, that B and not 

 A is struck by the cathode particle, then after the collision 

 B will be uncharged, while A has one unit of positive charge, 

 the total charge on the system is again one unit of positive 

 electricity ; but as B Las been deprived of its charge the 

 electrical attraction between A and B is very much less than 

 it was before the collision took place, so that the system 

 will be much more likely to break up into separate atoms 

 and supply us with a charged atom A. The negatively 

 electrified atom B will be a little less likely to be struck by 

 a negatively electrified cathode particle than the positively 

 electrified one A. On the other hand, when a collision did 

 take place, it would be easier to detach a corpuscle from the 

 negatively electrified B than from the positively electrified A. 



Similar considerations would apply to compounds as well 

 as to elements. We might in certain cases get some of the 

 atoms of a compound molecule liberated and not others. 

 Thus, if the hydrogen atoms in marsh-gas CH 4 are negatively 

 charged, and if one of them is struck by a cathode particle, 

 it would lose its charge and be easily detached, the other 

 hvdroo-en atoms which retained their charge would cling to 

 the carbon atom. 



The photographs hitherto described were made with 

 discharge-tubes whose volume was considerably greater 

 than 1000 c.c. ; I have also made some photographs when 

 the tube was very much smaller, the diameter being about 

 2 cm. The feature of these photographs is, that unless the 

 pressure is reduced very low, when the potential differ- 

 ence between the electrodes is very large, almost the only 

 thing to be seen on the plate, whatever gas may be in the 

 tube, is the secondary radiation, negatively as well as posi- 

 tively charged, corresponding to the hydrogen atom ; the 

 negative portion is not infrequently almost as bright as the 

 positive. 



When the tube is rilled with air, a very faint curve corre- 

 sponding to the oxygen atom can with difficulty be detected 

 on the plate ; it is, however, much too faint for reproduction 

 from a photograph. Though this line is so faint, it is remark- 

 able that it is generally the first to appear when the photograph 

 is developed ; the hydrogen line, though so much stronger 

 in the end, takes a much longer time to develop. It appears 

 as if the hydrogen atoms had penetrated much more deeply 

 into the film than the oxygen ones, but that close to the 



