96 



Prof. Tyndall on a New Series of 



[Recess, 



atoms ? Is the vis viva of the intercepted waves transferred to the molecule 

 as a whole, or to its constituent parts ? 



The molecule, as a whole, can only vibrate in virtue of the forces exerted 

 between it and its neighbour molecules. The intensity of these forces, and 

 consequently the rate of vibration, would, in this case, be a function of the 

 distance between the molecules. Now the identical absorption of the 

 liquid and of the vaporous nitrite of amyl indicates an identical vibrating 

 period on the part of liquid and vapour, and this, to my mind, amounts to an 

 experimental demonstration that the absorption occurs in the main within 

 the molecule. For it can hardly be supposed, if the absorption were the act 

 of the molecule as a whole, that it could continue to affect waves of the 

 same period after the substance had passed from the vaporous to the liquid 

 state. 



In point of fact the decomposition of the nitrite of amyl is itself to some 

 extent an illustration of this internal molecular absorption ; for were the ab- 

 sorption the act of the molecule as a whole, the relative motions of its 

 constituent atoms would remain unchanged, and there would be no me- 

 chanical cause for their separation. It is probably the synchronism of the 

 vibrations of one portion of the molecule with the incident waves which 

 enables the amplitude of those vibrations to augment until the chain which 

 binds the parts of the molecule together is snapped asunder. 



The liquid nitrite of amyl is probably also decomposed by light ; but the 

 reaction, if it exists, is incomparably less rapid and distinct than that of 

 the vapour. Nitrite of amyl has been subjected to the concentrated solar 

 rays until it boiled, and it has been permitted to continue boiling for a 

 considerable time, without any distinctly apparent change occurring in the 

 liquid *. 



I anticipate wide, if not entire, generality for the fact that a liquid and 

 its vapour absorb the same rays. A cell of liquid chlorine now preparing 

 for me will, I imagine, deprive light more effectually of its power of causing 

 chlorine and hydrogen to combine than any other filter of the luminous 

 rays. The rays which give chlorine its colour have nothing to do with this 

 combination, those that are absorbed by the chlorine being the really effec- 

 tive rays. A highly sensitive bulb containing chlorine and hydrogen in 

 the exact proportions necessary for the formation of hydrochloric acid was 

 placed at one end of the experimental tube, the beam of the electric lamp 

 being sent through it from the other. The bulb did not explode when the 

 tube was filled with chlorine, while the explosion was violent and im- 

 mediate when the tube was filled with air. I anticipate for the liquid 

 chlorine an action similar to but still more energetic than that exhibited by 

 the gas. If this should prove to be the case, it will favour the view that 



* On the 21st of October, Mr. Ernest Chapman mentioned to me in conversation 

 that he once exposed nitrite-of-amyl raponr to the action of light. With what result 

 I do not know. 



