104 FBAGMENTS OF SCIENCE. 



be regarded as an assemblage of such molecules, 

 question now before us is this : In the act of absorptio: 

 is it the molecules that are effective, or is it their co 

 stituent atoms? Is the vis viva of the intercep 

 light-waves transferred to the molecule as a whole, or 

 its constituent parts ? 



The molecule, as a whole, can only vibrate in virt 

 of the forces exerted between it and its neighbour mol 

 cules. The intensity of these forces, and consequent! 

 the rate of vibration, would, in this case, be a functi 

 of the distance between the molecules. Now the iden 

 tical absorption of the liquid and of the vaporous nitri 

 of amyl indicates an identical vibrating period on 

 part of liquid and vapour, and this, to my min 

 amounts to an experimental proof that the absorpti 

 occurs in the main within the molecule. For it 

 hardly be supposed, if the absorption were the act o 

 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 in- 

 ternal molecular absorption ; for were the absorption 

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

 of its constituent atoms would remain unchanged, and 

 there would be no mechanical cause.for their separation. 

 It is probably the synchronism of the vibrations of one 

 portion of the molecule with the incident waves, that 

 enables the amplitude of those vibrations to augment, 

 until the chain which binds the parts of the molecule 

 together is snapped asunder. 



I anticipate wide, if not entire, generality for th 

 fact that a liquid and its vapour absorb the same rays 

 A cell of liquid chlorine would, I imagine, deprive ligh 

 more effectually of its power of causing chlorine an 



