ADDRESS. 23 



the end of the chain as another.' It is interesting to observe, however, 

 that Black was evidently well acquainted with the work of Amontons, 

 and strongly supports his inference as to the nature of air. Thus, in dis- 

 cussing the general cause of vaporisation, Black says that some philoso- 

 phers have adopted the view • that every palpable elastic fluid in nature 

 is produced and preserved in this form by the action of heat. Mr. 

 Amontons, an ingenious member of the late Royal Academy of Sciences, 

 at Paris, was the first who proposed this idea with respect to the atmo- 

 sphere. He supposed that it might be deprived of the whole of its 

 elasticity and condensed and even frozen into a solid matter were it in 

 our power to apply to it a sufficient cold ; that it is a substance that 

 differs from others by being incomparably more volatile, and which is 

 therefore converted into vapour and preserved in that form by a weaker 

 heat than any that ever happened or can obtain in this globe, and which 

 therefore cannot appear under any other form than the one it now wears, 

 so long as the constitution of the world remains the same as at present.' 

 The views that Black attributes to Amontons have been generally asso- 

 ciated with the name of Lavoisier, who practically admitted similar 

 possibilities as to the nature of air ; but it is not likely that in such 

 matters Black would commit any mistake as to the real author of a parti- 

 cular idea, especially in his own department of knowledge. Black's own 

 special contribution to low-temperature studies was his explanation of the 

 interaction of mixtures of ice with salts and acids by applying the doctrine 

 of the latent heat of fluidity of ice to account for the frigorific effect. In 

 a similar way Black explained the origin of the cold produced in Cullen's 

 remarkable experiment of the evaporation of ether under the receiver of 

 an air-pump by pointing out that the latent heat of vaporisation in this 

 case necessitated such a result. Thus, by applying his own discoveries to 

 latent heat. Black gave an intelligent explanation of the cause of all the 

 low-temperature phenomena known in his day. 



After the gaseous laws had been definitely formulated by Gay-Lussac 

 and Dalton, the question of the absolute zero of temperature, as deduced 

 from the properties of gases, was revived by Clement and Desormes. 

 These distinguished investigators presented a paper on the subject to the 

 French Academy in 1812, which, it appears, was rejected by that body. 

 The authors subsequently elected to publish it in 1819. Relying on 

 what we know now to have been a faulty hypothesis, they deduced from 

 observations on the heating of air rushing into a vacuum the temperature 

 of minus 267 degrees as that of the absolute zero. They further en- 

 deavoured to show, by extending to lower temperatures the volume or the 

 pressure coefficients of gases given by Gay-Lussac, that at the same 

 temperature of minus 267 degrees the gases would contract so as to 

 possess no appreciable volume, or, alternatively, if the pressure was under 

 consideration, it would become so small as to be non-existent. Although 

 full reference is given to previous work bearing on the same subject, yet, 

 curiously enough, no mention is made of the name of Amontons. It 



