(e409 
VIII.—WNote as to the Dynamical Equivalent of Temperature in Liquid Water, and 
the Specific Heat of Atmospheric Air and Steam, being a Supplement to a Paper 
On the Mechanical Action of Heat. By Witt1am Jonn Macquorn RankINE, 
Civil Engineer, F.R.S.E., F.R.S.S.A., &c. 
(Read 2d December 1850.) 
(33*.) In my paper on the Mechanical Action of Heat, published in the 1st 
Part of the 20th Volume of the Transactions of the Royal Society of Edinburgh, 
some of the numerical results depend upon the dynamical equivalent of a degree 
of temperature in liquid water. The value of that quantity which I then used, was 
calculated from the experiments of DE La Rocur and Bérarp on the apparent 
specific heat of atmospheric air under constant pressure, as compared with liquid 
water. 
The experiments of Mr You.e on the production of heat by friction, give, for 
the specific heat of liquid water, an equivalent about one-ninth part greater than 
that which is determined from those of De ta Rocur and Bérarp. I was for- 
merly disposed to ascribe this discrepancy in a great measure to the smallness of 
the differences of temperature measured by Mr Jouts, and to unknown causes 
of loss of power in his apparatus, such as the production of sound and of electri- 
city; but, subsequently to the publication of my paper, I have seen the detailed 
account of Mr Jouxe’s last experiments in the Philosophical Transactions for 
1850, which has convinced me, that the uncertainty arising from the smallness 
of the elevations of temperature, is removed by the multitude of experiments 
(being forty on water, fifty on mercury, and twenty on cast iron); that the agree- 
ment amongst the results from substances so different, shews that the error by 
unknown losses of power is insensible, or nearly so; and that the necessary con- 
clusion is, that the dynamical value assigned by Mr Jou te to the specific heat of 
liquid water, viz. :—772 feet per degree of Fahrenheit, does not err by more than 
two, or, at the utmost, three feet; and therefore, that the discrepancy originates 
chiefly in the experiments of Dz La Rocuz and Brrarp. 
I therefore take the earliest opportunity of correcting such of my calculations 
as require it, so as to correspond with Mr Joun’s equivalent. They relate to the 
specific heat of atmospheric air as compared with liquid water, and to that of 
steam, and are contained in the second and third Sections of my paper, Articles 14 
and 20; Equations 28, 34, and 36. 
VOL. XX. PART IL. 5 3 E 

