307 



May 26, 1853. 

 The EARL OF ROSSE, President, in the Chair. 



The following communications were read : — 



1. A letter from Mr. Joule to Colonel Sabine. Communicated 

 by Col. Sabine, Treas. V.P.R.S. &c. 



Acton Square, Salford, May 23, 1853. 



My dear Sir, — I notice in the Proceedings of the Royal Society 

 for April 21, a letter from M. Regnault in which some experiments 

 of my own are referred to in a manner which I feel does me injus- 

 tice. M. Regnault says, " Le nombre trouve par M. Joule pour la 

 chaleur specifique de I'air sous pression constante (0"226) est beau- 

 coup trop faible. Celui qui resulte de mes experiences tres nom- 

 breuses, et faites dans des circonstances variees, afin de reconnaitre 

 et d'eliminer les erreurs constantes, est 0"237." 



Now, in my paper on the air-engine, Phil. Trans. 1852, part i. 

 p. 74, I have given the results of three series of experiments, viz, 

 0-23008, 0-22674, and 0-2325, and remark, " The mean of the three 

 results is 0*22977, or nearly 0-23, which we may take as the specific 

 heat of air at constant pressure determined by the above experiments." 



I had been informed that M. Regnault v/as w^orking on the spe- 

 cific heat of gases, and on that account did not feel it desirable to 

 enter upon the laborious investigation which would have been re- 

 quisite in order to add a couple of decimal figures to the number I 

 had arrived at, and which was sufficient for the object I had in view, 

 viz. to show that the discrepancy between the actual and theoreti- 

 cal velocity of sound arose from the incorrectness of Delaroche and 

 Berard's determination of the specific heat of air (2-67), and not 

 from any notable error in my number for the mechanical equivalent 

 of the thermal unit. Having succeeded in doing this, I calculated 

 the Tables 3 and 4 of my paper, using 0'238944 for the specific heat 

 of air under constant pressure. I feel much gratified that the result 

 arrived at by so eminent an experimentalist as M. Regnault confirms 

 the accuracy in the main of the number I adopted. 



I have only to add that Professor Thomson and myself, in pursu- 

 ing our research on the thermal effects of rushing elastic fluids, are 

 following up the views on the relation between mechanical and 

 thermal phenomena originated by ourselves ; and we shall feel most 

 happy if M. Ptegnault's results, in the important line of investiga- 

 tion he has adopted, will facilitate our labour. 



I have the honour to remain, dear Sir, 



Yours most truly. 



Colonel Sabine, &;c. &;€. 8fC. J. P. Joule. 



2. " Experimental Researches on Vegetation." By M. Georges 

 Ville. Communicated by The Earl of Rosse, P. U.S. Received 

 May 26. 



After stating that it has often been asked if air, and especially 



