THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



OCTOBER 1865. 



XXXII. On the Second Law of Thermodynamics. By W. J. 

 Macquorn Rankine, C.E., LL.D., F.R.SS.L.fyE. §•<?.* 



1. TT has long been established that all the known relations 

 J- between heat and mechanical energy are summed up in 

 two laws, called respectively the first law and the second law of 

 thermodynamics : viz., 



First Law. — Quantities of heat and of mechanical energy are 

 convertible at the rate very nearly of 772 foot-pounds to the 

 British (or Fahrenheit-avoirdupois) unit, or 424 kilogrammetres 

 to the French (or Centigrade-metrical) unit of heat. 



Second Law. — The quantity of energy which is converted 

 from one of those forms to the other during a given change of 

 dimensions and condition in a given body, is the product of the 

 absolute temperature into a function of that change, and of the 

 kind and condition of the matter of the body. 



By absolute temperature is here to be understood temperature 

 measured according to a scale so graduated that the tempera- 

 ture of a homogeneous body shall vary in the simple proportion 

 of the quantity of energy it possesses in the form of sensible or 

 thermometric heat. 



2. The laws of thermodynamics, as here stated, are simply 

 the condensed expression of the facts of experiment. But they 

 are also capable of being viewed as the consequence of the sup- 

 position that the condition of bodies which accompanies the 

 phenomena of sensible heat consists in some kind of motion 

 amongst their particles. 



3. The first law would obviously follow from the supposition 



* Communicated by the Author, having been read to the British Asso- 

 ciation, Section A, at Birmingham, September 1865. 



Phil Mag. S. 4. Vol. 30. No. 203. Oct. 1865. R 



