92 ATOMS, MOLECULES, 



tion of radiant heat was determined, first for the liquid 

 layer, and then for its equivalent vaporous layer. As 

 before, a representative experiment or two will suffice for 

 illustration. When the substance was sulphuric ether, 

 and the source of radiant heat an incandescent platinum 

 spiral, the absorption by the column of vapour was 

 found to be 6 6 -7 per cent, of the total beam. The 

 absorption of the equivalent liquid layer was next de- 

 termined, and found to be 67 '2 per cent. Liquid and 

 vapour, therefore, differed from each other only 0'5 per 

 cent. : In other words, they were practically identical 

 in their action. The radiation from the lime-light has 

 a greater power of penetration through transparent 

 substances than that from the spiral. In the emission 

 from both of these sources we have a mixture of obscure 

 and luminous rays ; but the ratio of the latter to the 

 former, in the lime-light, is greater than in the spiral ; 

 and, as the very meaning of transparency is perviousness 

 to the luminous rays, the emission in which these rays 

 are predominant must pass most freely through trans- 

 parent substances. Increased transmission implies dimi- 

 nished absorption ; and, accordingly, the respective ab- 

 sorptions of ether vapour and liquid ether when the 

 lime-light was used, instead of being 6 6 '7 and 67*2 per 

 cent., were found to be 



Vapour . . 33-3 per cent. 



Liquid .... 33'3 



no difference whatever being observed between the two 

 states of aggregation. The same was found true of 

 hydride of amyl. 



This constancy and continuity of the action exerted 

 on the waves of heat when the state of aggregation is 

 changed I have called 'the thermal continuity of 

 liquids and vapours.' It is, I think, the strongest 



