5 



4. On the Mechanical Action of Heat. By W.J. Macquorn 

 Rankine, Esq. Note as to the Dynamical Equivalent of 

 Temperature in Liquid Water, and the Specific Heat of 

 Atmospheric Air and Steam. 



In the author's paper on the Mechanical Action of Heat (Trans. 

 Roy. Soc. Edin., Vol. xx., Part 1), the calculations depending on 

 the dynamical equivalent of temperature in liquid water were founded 

 on the experiments of De la Roche and Berard on the ratio of the 

 apparent specific heat of atmospheric air under constant pressure to 

 that of water. The equivalent thus obtained was about one-tenth 

 part less than Mr Joule's. Since then, the author, having become 

 acquainted with the details of Mr Joule's experiments, has come to 

 the conclusion that Mr Joule's equivalent is correct to about 5J5 of 

 its amount, and that the discrepancy in question originates chiefly 

 in the experiments of De la Roche and Berard. The calculations 

 requiring correction from this circumstance are contained in the se- 

 cond and third sections of the above-mentioned paper, articles 14 

 and 20, equations 28, 34, and 36. The following is a summary of 

 the corrected results : — 



Dynamical specific heat of liquid water, as determined by Mr 

 Joule from experiments on friction (Phil. Trans., 1850) — 



Metres. Feet. 



Per centigrade degree, . 423-54 1389-6 



Per degree of Fahrenheit 772 



Specific heat of atmospheric air, that of liquid water being taken 

 as unity — 



Real, 01717 



Apparent, under constant pressure, .... 0*2404 

 (The same, according to De la Roche and Berard, 0-2669) 



Dynamical specific heat of steam — 



Metres per Feet per Ft. per deg. 



Centig. degree. Centig. degree. of Fahr. 



Real, 82-40 269-35 149-64 



Apparent, under constant pressure, 129-18 422-83 23546 



Ratio of those two specific heats, I : 1'57. 



