108 



Anniversary Meeting. 



[Nov. 30, 



meter with the mercurial thermometer, upon the elastic force of aqueous 

 vapour, upon the determination of the density of gases, and upon hygro- 

 metry must excite the astonishment of all who can estimate the difficulty of 

 the problems attacked, the precision of the results attained, and the funda- 

 mental character of the data which he has determined. 



These researches were published before the year 1850 ; many of them 

 were embodied in the first volume of his 1 Relation des Experiences pour 

 determiner les lois et les donnees physiques necessaires au calcul des Ma- 

 chines a Feu." The Royal Society marked their sense of the importance 

 of these earlier labours of M. Regnault by the presentation of the Rumford 

 Medal in the year 1848. 



He has since published the second volume of that great work, to 

 which more especially the Copley Medal is now awarded. It embraces a 

 series of researches even more delicate and difficult ; to use the words of 

 one whose recent loss we all deplore, and whose opinion on this subject 

 possesses a weight which is equalled by few, viz. the late Mr. Graham, " in 

 these researches a degree of precision is attained, where precision is all- 

 important, which appears never to have been surpassed, or perhaps even 

 approached before in similar inquiries. The results are data of a funda- 

 mental character, to the completion of which chemists and natural philoso- 

 phers have been looking anxiously for years past, and which they have 

 now received from the hands of M. Regnault with a feeling of entire 

 confidence." 



The researches on the specific heat of gases and vapours, alone, consti- 

 tute a monumental work. Upon this subject the most discordant results 

 had been obtained by experimental investigators of tried skill and inge- 

 nuity ; and the problem, notwithstanding its importance, exhibited a series 

 of perplexing contradictious. 



Before commencing his own experiments, M. Regnault submitted the 

 various methods of previous inquirers on the subject to a minute compa- 

 rison and criticism, particularly those of Delaroche and Berard, of Hay- 

 craft, and of Apjohn and Suesman. M. Regnault finally adopted a method 

 based upon the one proposed by Delaroche and Berard. The principle 

 of it may be explained in a few words. 



A current of the compressed gas under experiment is made to traverse 

 at a uniform velocity a metallic worm maintained at a uniform temperature. 

 The heated gas is then transmitted through a calorimeter, and the amount 

 of the following quantities determined, viz. : — 1, the weight of the gas 

 employed ; 2, the cooling of the gas ; 3, the rise of temperature of the 

 water in the calorimeter. From these data the specific heat of the gas is 

 calculated. 



Amongst various special contrivances required for avoiding error, it w;is 

 necessary to have the means of regulating the escape of the gas with suffi- 

 cient uniformity, and for preventing its issue from the calorimeter at vary- 

 ing pressures. 



