
( 565.) 
XL.—On the Mechanical Action of Heat. By Wittiam JoHn Macquorn RANKINE, 
Civil Engineer, F.R.S.E., F.R.S.S.A., &c. 
(Read January 17, 1853.) 
Section VI.—A Review oF THE FUNDAMENTAL PRINCIPLES OF THE MECHANICAL 
THEORY OF HEAT; WITH REMARKS ON THE THERMIC PHENOMENA OF CURRENTS 
oF ELastic FLUIDS, AS ILLUSTRATING THOSE PRINCIPLES. 
(Article 46.) I have been induced to write this Section, in continuation of a 
paper on the Mechanical Action of Heat, by the publication (in the Philosophical 
Magazine for December 1852, Supplementary Number) of a series of experiments 
by Mr Joute and Professor Wittiam Tomson, on the Thermal Effects expe- 
rienced by Air in rushing through small Apertures. Although those authors 
express an intention to continue the experiments on a large scale, so as to obtain 
more precise results; yet the results already obtained are sufficient to constitute 
the first step towards the experimental determination of that most important 
function in the theory of the mechanical action of heat, which has received the 
name of Carnot’s Function. 
By the theoretical investigations of Messrs CLausius and Taomson,—which are 
based simply on the fact of the convertibility of heat and mechanical power, 
the determination of their relative value by Mr Jous, and the properties of the 
function called temperature, without any definite supposition as to the nature of 
heat,—Carnor’s function is left wholly indeterminate. 
By the investigations contained in the previous sections of this paper, and in 
a paper on the Centrifugal Theory of Elasticity,—in which the supposition is made, 
that heat consists in the revolutions of what are called Molecular Vortices, so 
that the elasticity arising from heat is in fact centrifugal force,—a form is assigned 
to Carnot’s function; but its numerical values are left to be ascertained by expe- 
riment. 
The recent experiments of Messrs JouLe and THomson serve (so far as the 
degree of precision of their results permits) at once to determine numerical values 
of Carnot’s function for use in practice, and to test the accuracy with which 
the phenomena of heat are represented by the consequences of the hypothesis 
of molecular vortices, from which the investigation in this paper sets out. 
VOL. XX. PART IV. 70 
