670 Sir J. J. Thomson on 



same condition, and so acquired the same amount of kinetic 

 energy. 



The question now arises as to how the mercury atom 

 acquires these very various charges. When a mercury atom 

 is ionized, can it lose any number of corpuscles from one to 

 eight? Taking for example a mercury atom with 5 positive 

 charges, has it got into this condition by losing 5 corpuscles 

 when it was ionized, or did it originally lose the maximum 

 number 8 and regain 3 subsequently ? The photographs 

 prove, I think, that the second supposition is the correct one, 

 and that in the discharge-tube there are two, and only two, 

 kinds of ionization; in one of these kinds the mercury atom 

 loses 1 corpuscle, while in the other kind it loses 8, and that 

 there are no indications of ionization of such a character as 

 to deprive the mercury atom of 7, 6, 5, 4, 3, or 2 corpuscles. 



The evidence for this is as follows : let us suppose for a 

 moment that atoms with any charge from 1 to 8 were pro- 

 duced by the ionization of the mercury atoms in the discharge- 

 tube. Consider now the parabola due to the mercury atom 

 which, when it passed through the electric and magnetic 

 fields, had one positive charge. This parabola would result 

 from atoms of the following kinds : — 



1. Atoms which had lost 8 corpuscles on ionization and 



regained 7 ; 



2. Atoms which had lost 7 and regained 6 ; 



3. Atoms which had lost 6 and regained 5, 



and so on, the eighth and last members of the series being- 

 atoms which had lost one corpuscle on ionization and had 

 not regained it. 



The parabola on the photographic plate would be due to 

 the superposition of the 8 parabolas due to these types of 

 atoms. 



If 8d is the horizontal distance from the vertical axis of 

 the head of the parabola due lo the atom which lost one 

 corpuscle on ionization, the horizontal distances of the heads 

 of the parabolas due to atoms of the 1st, 2nd, 3rd types will 

 be respectively 8d[$, 8d\l , 8d/6, 8d/5, 8djf4, 8<*/3, 8d/2, 8d. 

 Thus up to the horizontal distance Sd/7 there would be only 

 one parabola, at Sd/7 another parabola would be added, this 

 would produce an abrupt increase in the intensity of the 

 photograph, there would be another abrupt increase at 8d/G, 

 another at 8d/5, and so on. Thus the intensity of the para- 

 bola on the photograph would not be continuous, there would 

 be places where the intensity was suddenly increased giving 

 a beaded appearance to the photograph. The abrupt increase 

 at 8d is very marked on this parabola, the others are not 



