380 



Dr. G. J. Stoney on the 



excess of energy, or the combination with oxygen takes place, 

 whichever event comes first. 



The summary of the results of this recent investigation 

 have been here translated into molecular language, to serve 

 as an example of the additional insight which we may already 

 hope to gain into the chemistry of nature by adopting the 

 molecular standpoint; and whenever the secret of the motions 

 of electrons within molecules becomes known this insight will 

 doubtless be vastly increased. Through the spectroscope we 

 seem to be on the borderland of this great discovery. 



Reference has been made to chemical reaction, friction, and 

 the disruption of a crystal, as events which may bring into a 

 state of activity some of the electrons associated with Bb 

 motions. Another event which seems to have this effect is 

 the gaseous encounter between two molecules of the same 

 kind. A suggestive experiment was made in the laboratory 

 of the Royal Dublin Society, when Professor Emerson Rey- 

 nolds, F.R.S., and the present author were engaged in 

 examining the spectra of coloured vapours (Philosophical 

 Magazine, July 1871, p. 41). We had examined the 

 splendid absorption-spectrum of chlorochromic anhydride 

 mixed with air. Here the encounters that the molecules of 

 the vapour met with were most of them encounters with 

 molecules of air, the minority only being encounters between 

 molecules of the vapour. If the vessel containing the vapour 

 be freed from air, the encounters between molecules of the 

 vapour will be present in the same number as before, while 

 all encounters between air and vapour will be absent. Hence 

 we argued (for at that time we supposed the motions in the 

 molecules to have been evoked by the undulation in the 

 aether)*, that the molecules being less knocked about should 

 produce a spectrum of lines that would be less diffuse. On 

 trying the experiment, however, we found that the spectrum 

 was sensibly the same as before. From this observation it 

 would appear that the motions to which the spectrum is due 

 are affected by the encounters between molecules of the 



* The amplitude of the EZ> motions which the undulation in the aether, 

 if acting alone, can develop is apparently tco email ; and this is probably 

 because, at this 'small amplitude, the transference of energy from 136 

 motions to Ba and A motions is inconspicuous. "Where this is the case 

 the aMhcrial undulation acting alone upon the gas cannot suffer any 

 sensible amount of absorption. Lut the coi ditions are altogether differ- 

 ent if some other agency produces an amplitude which can freely part 

 with its energy by conduction, and which at the same time can be acted 

 on by the (ether in the direction which tends to keep the amplitude up. 

 Under these circumstances there will be active withdrawal of energy 

 from the aether, and an absorption-spectrum will result. This seems to 

 be what happens in coloured gases. 

 [Added September 1895. — What seems a simpler and therefore more 



