236 Sir J. J. Thomson 



on 



in fact so near as to make it difficult to distinguish between 

 them, but the measurements I have made of the value of m/e 

 for the radiation in this case have consistently given me 

 values much nearer 7 than 6. and distinctly higher than 

 those with carbon compounds. If the electric atomic weight 

 is 7, it may possibly be the atom of nitrogen w T ith a double 

 charge, though nitrogen is, as a rule, loth to appear in the 

 positive rays. It only occurs with a positive charge, which 

 makes it unlikely that it is an atom of oxygen with a double 

 charge, as oxygen has a great tendency to appear with a 

 negative charge. In some cases this secondary radiation is 

 the strongest on the plate. 



In helium the strongest radiation of the type we are con- 

 sidering is one with an electric atomic weight equal to 12 ; 

 this is indicated by the continuous line passing through the 

 origin in fig. 11. The experiments already described show 

 that this radiation is due to particles which are charged when 

 they pass through the opening in the cathode, but some of 

 which lose their charges as they pass through the electric and 

 magnetic fields. We have thus here a case of recombination 

 rather than that of a true secondary radiation or dissociation 

 such as that which produces the radiation with atomic 

 weights 1, 3, 6. The radiation with atomic weight 12, when 

 the gas is helium, has not been found with a negative charge. 

 Its atomic weight suggests that the carrier of this radiation 

 is the aggregate (He) 3 + . 



In oxygen I have noticed three kinds of radiation of the 

 type we are considering, having respectively the electric 

 atomic weights 16, 48, 96. The first of these corresponds 

 to the atom of oxygen — it is much the strongest of the three ; 

 the second to (0 3 ) + , a molecule of ozone with one positive 

 charge ; while the third corresponds to (0 6 ) + . It is in- 

 teresting to note that Ladenburg and Lehmann (Ann. tier 

 Phys. xxi. p. 315) found that a more complex polymer of 

 oxygen than ozone was produced w r hen the electric discharge 

 passed throuch oxygen at a low pressure. They succeeded 

 in freezing this modification out of the gas with the aid of 

 liquid air, and ascribed to its molecule the composition 6 . 

 The secondary radiation corresponding to 3 and 6 is feeble. 

 1 have not yet been able to detect any of it with a negative 

 charge. The secondary radiation with a negative charge 

 corresponding to the oxygen atom is extremely w r ell marked; 

 indeed, after H_ it is generally the most pronounced con- 

 stituent of the negatively charged radiation. In the primary 

 radiation in oxygen the radiation consists of + and (0 2 ) + . 

 The rays for oxygen are showm in fig. 16. 



