1864.] Vvof.TyndaW—'Contnbutioiis fo Molecular Physics, 161 



intangible and mysterious ether in which that matter is immersed. The 

 natural philosophy of the future must mainly consist in the examination of 

 the relations of these two substances. The hope of being able to come 

 closer to the origin of the ethereal wayes, to get some experimental hold of 

 the molecules whence issue the undulations of light and heat, has stimulated 

 the author in the labours which haye occupied him for the last five years, 

 and it is this hope, rather than the desire to multiply the facts already 

 known regarding the action of radiant heat, which prompted his present 

 inyestigation. 



He had already shown the enormous differences which exist between 

 gaseous bodies, as regards both their power of absorbing and emitting 

 radiant heat. AYhen a gas is condensed to a liquid, or a liquid congealed 

 to a solid, the molecules coalesce, and grapple with each other, by forces 

 which were insensible as long as the gaseous state was maintained. But 

 though the molecules are thus drawn together, the ether still surrounds 

 them : hence, if the acts of radiation and absorption depend on the indi- 

 yidual molecules, they will assert their power eyen after their state of 

 aggregation has been changed. If, on the contrary, their mutual entangle- 

 ment by the force of cohesion be of paramount influence in the interception 

 and emission of radiant heat, then we may expect that liquids will exhibit a 

 deportment towards radiant heat altogether different from that of the yapour 

 from which they are derived. 



The first part of the present inquiry is devoted to an exhaustiye examina- 

 tion of this question. The author employed twelve different liquids, and 

 operated upon five different layers of each, which varied in thickness 

 from 0"02 of an inch to 0*2 7 of an inch. The liquids were enclosed, not 

 in glass vessels, which would have materially modified the heat, but between 

 plates of transparent rock-salt, which but slightly affected the radiation. 

 His source of heat throughout these comparative experiments consisted of 

 a spiral of platinum wire, raised to incandescence by an electric current of 

 unvarying strength. The quantities of radiant heat absorbed and trans- 

 mitted by each of the liquids at the respective thicknesses were first deter- 

 mined ; the vapours of these liquids were subsequently examined, the 

 quantities of vapour employed being proportional to the quantities of liquid 

 trayersed by the radiant heat. The result of the comparison was that, for 

 heat of the same quality, the order of absorption of liquids and that of 

 their vapours are identical. There was no exception to this law ; so that, to 

 determine the position of a vapour as an absorber or radiator, it is only 

 necessary to determine the position of its liquid. 



This result proves that the state of aggregation, as far, at all events, as 

 the liquid stage is concerned, is of altogether subordinate moment — a con- 

 clusion which will probably prove to be of cardinal moment in molecular 

 physics. On one important and contested point it has a special bearing. If 

 the position of a liquid as an absorber and radiator determine that of its 



