144 Professor Sir J. J. Thomson [April 7, 



The atomic weights represented in this 



18-5 C1++ 

 27-7 CO 

 36-0 C1+ 

 46-5 CC1+ 

 63 (?) faint 

 81 CClo+ 

 102 Hg++ 

 201 Hg+ 



The carriers with atomic weights 1*5 and 3 have not been iden- 

 tified. They are of freqnent occurrence. I have here two sHdes, one 

 of SiH4 and the other of the residual gas in tube after the air has 

 been pumped out, in which they are well marked, though at their 

 best they are only faint lines. 



Let us now consider some of the results brought to light by these 

 photographs. In the first place, they show that a gas through which 

 an electric discharge is passing is a much more complex thing than 

 a collection of molecules all equal to each other. Even an elementary 

 gas becomes under these circumstances a mixture of a great many 

 different substances. Thus, to take oxygen as an example, the 

 photographs show tljat when a current of electricity passes through 

 it, we may have present simultaneously oxygen in the following 

 states : — 



1. Ordinary molecular oxygen, O2. 



2. Neutral atoms of oxygen, 0. 



3. Atoms of oxygen with 1 positive charge, 0+. 



4. Atoms of oxygen with 2 positive charges, 0^+. 



5. Atoms of oxygen with 1 negative charge, 0_. 



6. Molecules of oxygen with 1 positive charge, O2+. 



7. Ozone with a positive charge, Og^. 



8. Og with a positive charge, Og. 



And, in addition, there are free negative corpuscles. Thus in the 

 elementary gas there are at least nine (the list has no claim to be 

 exhaustive) separate substances present when the discharge passes 

 through it. Each of these substances has almost certainly different 

 properties, possibly a characteristic spectrum. If we took any other 

 gas we should find that the same thing would be true : thus in 

 hydrogen we have H, Ho, H+, H_, Hj.^, even if we do not ascribe 

 to hydrogen the lines giving m/e = 1*5 or 3. In nitrogen we have 

 jST, Nsj ^+) N++) ^2+5 carbon occurs as C+, 0+^., C_, chlorine as 

 CI, CI2, C1+, C1++ and Cl_, mercury as Hg, Hg+, Hg++, and pro- 

 bably as Hg++, as there is a very persistent line for which m/e is 

 about 66. 



