469 



May 10M, I860. 

 Sir BENJAMIN C. BRODIE, Bart., President, in the Chair. 



The following Gentlemen were proposed by the Council for .Elec- 

 tion as Foreign Members, and it was announced that they would be 

 balloted for at the ensuing Meeting of the Society, viz. 



Alexander Dallas Bache. 



Hermann Helmholtz. 



Albert Kolliker. 



Philippe Edouard Poulletier de Verneuil. 



The Bakerian Lecture was then delivered by Mr. Fairbairn, F.R.S. 



The Lecturer gave a condensed exposition of the experiments and 

 results detailed in the following Paper. He also exhibited the appa- 

 ratus employed, and explained the methods followed. 



" Experimental Researches to determine the Density of Steam 

 at all Temperatures, and to determine the Law of Expan- 

 sion of Superheated Steam." By WILLIAM FAIRBAIRN, Esq., 

 F.R.S., and THOMAS TATE, Esq. 



(Abstract.) 



The object of these researches is to determine by direct experiment 

 the law of the density and expansion of steam at all temperatures. 

 Dumas determined the density of steam at 212 Fahr., but at this 

 temperature only. Gay-Lussac arid other physicists have deduced 

 the density at other temperatures by a theoretical formula true for a 



perfect gas : 



VP_459 + T 



VJP, 459 + T X 



On the expansion of superheated steam, the only experiments are 

 those of Mr. Siemens, which give a rate of expansion extremely high, 

 and physicists have in this case also generally assumed the rate of 

 expansion of a perfect gas. Experimentalists have for some time 

 questioned the truth of these gaseous formulae in the case of conden- 

 sable vapours, and have proposed new formulae derived from the 

 dynamic theory of heat ; but up to the present time no reliable direct 



