226 Sir J. J. Thomson : Furtl 



lev 



to combine is merely the velocity o£ the positive rays them- 

 selves. In the dark space in front of the cathode there is an 

 intense electric field in which the corpuscles are moving far 

 faster than the positive rays, so that the relative velocity of 

 the positive rays and the corpuscles is very much greater 

 than on the other side of the cathode. Thus the union of a 

 positive ray and a negative corpuscle is far less likely to 

 occur in the dark space than when the positive ray has 

 passed through the cathode. 



The third suggestion, that the loss of kinetic energy is due 

 to collisions between the positive rays and the molecules 

 through which they are moving in the discharge-tube, is open 

 to the objection that it would produce effects of the same 

 general character on all the lines on the plate. As a matter 

 of fact, however, we find that some of the lines, notably 

 those of compounds formed by the action of the electric 

 discharge when it passes through mixed gases, are quite short, 

 showing that all the rays have much the same kinetic energy. 

 On the other hand, many of the lines are long and of nearly 

 equal intensity along the whole of their length ; while fre- 

 quently abrupt alternations of intensity occur along the lines, 

 giving them a beaded appearance. It is remarkable that 

 this beading may occur on some lines, while other lines on 

 the same plate are free from it. 



The second explanation seems to me to be the most probable 

 one, viz., that the positive rays are produced at different 

 places in the dark space, and so fall through different 

 potential differences and acquire different velocities. 



One of the most striking things brought to light by the 

 photographs is the extent to which the molecules of the gas 

 filling the tube are broken up by the electric discharge. 

 The dissociation which occurs in the gas is far greater than 

 that required to make the gas a conductor of electricity ; for 

 all that would be required for this purpose would be for some 

 of the molecules to lose a corpuscle and thus become 

 positively charged : these would be able to carry the positive 

 electricity, while the negative could be carried by the cor- 

 puscles or by molecules on which corpuscles had settled ; a 

 process of this kind would not involve the disintegration of 

 molecules into atoms. The photographs show, however, that 

 something much more complicated than this goes on in the 

 dark space and the negative glow, for on all the photographs 

 there are lines indicating atoms as well as those corresponding 

 to molecules, and instead of there being only one type 

 of carrier for the positive electricity, there are in general a 



