XVII 



CONTRIBUTIONS TO MOLECULAR PHYSICS 1 



HAYING on previous occasions dwelt upon the 

 enormous differences which exist among gaseous 

 bodies both as regards their power of absorbing 

 and emitting radiant heat, I have now to consider the 

 effect of a change of aggregation. When a gas is con- 

 densed to a liquid, or a liquid congealed to a solid, the 

 molecules coalesce and grapple with each other by forces 

 which are insensible as long as the gaseous state is main- 

 tained. But, even in the solid and liquid conditions, the 

 luminiferous ether still surrounds the molecules: hence, 

 if the acts of radiation and absorption depend on them 

 individually, regardless of their state of aggregation, the 

 change from the gaseous to the liquid state ought not ma- 

 terially to affect the radiant and absorbent power. If, on 

 the contrary, the mutual entanglement of the molecules 

 by the force of cohesion be of paramount influence, then 

 we may expect that liquids will exhibit a deportment 

 toward radiant heat altogether different from that of the 

 vapors from which they are derived. 



The first part of an inquiry conducted in 1863-64 was 

 devoted to an exhaustive examination of this question. 

 Twelve different liquids were employed, and five different 



1 A discourse delivered at the Royal Institution, March 18, 1864 supple- 

 menting, though of prior date, the Rede Lecture on Radiation. 



(407) 



