THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



JANUARY 1854. 



I. On the Mechanical Action of Heat. By William John 

 Macquorn Rankine, C.E., F.R.SS. Lond. and Edinb. ^"c* 



Prefatory Remarks. 



BY the permission of the Council of the Royal Society of 

 Edinburgh, the following series of communications are 

 republished, which, having been i-ead to the meetings of that 

 body at various periods during the sessions of 1849-50 and 

 1850-51, were first printed in the First and Second Parts of 

 the Twentieth Volume of their Transactions. 



These investigations may be considered under a twofold 

 aspect, — either as determining the theoretical and practical re- 

 sults, so far as heat and expansive power are concerned, of the 

 law of the mutual convertibility of physical powers, or as deve- 

 loping the consequences of an hypothesis respecting the consti- 

 tution of matter, called that of Molecular Vortices, whereby that 

 law, as respects heat and elasticity, is made a particular case of 

 the mechanical principle of the conservation of vis viva. 



The law of the mutual convertibility of physical powers has 

 long been a subject of abstract speculation, and may appear to 

 some minds in the light of a necessary truth. As we cannot, 

 however, expect it to be generally received as such, its practical 

 demonstration must be considered as having been effected by 

 the experiments of Mr. Joule. 



In the following paper, as it originally appeared, the mecha- 

 nical equivalent of the heat required to raise the temperature of 

 a given mass of liquid water by one degree was calculated inde- 

 pendently of those experiments, from the observed velocity of 

 sound in air, and from the specific heat of air under constant 



* CoiTimunicatcd I)}' the Author. 

 Phil. May. S. 4. Vol. 7. No. 42. Jan. 1854. B 



