150 
MR. MACQUORN RANKINE ON THERMO-DYNAMICS. 
whose real specific heat is equal to its specific heat at constant volume, being 
[234-6 feet of fall per Centigrade degree, or 
U K y \ 
[130*3 feet of fall per degree of Fahrenheit ; 
whose specific heat at constant pressure (as determined by M. Regnault) is 0 - 238x 
the specific heat of liquid water, or 
K P = 
[330’8 feet of fall per Centigrade degree, or 
[ 183*8 feet of fall per degree of Fahrenheit ; 
the ratio of these two quantities being 
g = I+N=l-41, 
as calculated from the velocity of sound. 
The volume occupied by an avoirdupois pound of air, at the temperature of melting 
ice, under the pressure of one pound on the square foot, as calculated from the ex- 
periments of M. Regnault, is 
P 0 V 0 =26214*4 cubic feet. 
This represents also the length in feet of a column of air of uniform density and 
sectional area, whose weight is equal to its elastic pressure on the area of its section 
at the temperature of melting ice. 
It will be found convenient, in expressing the temperature, as measured from the 
point of absolute cold, to make the following substitution : — 
r—K— T+T 0 , (41.) 
where T represents the temperature as measured on the ordinary scale from the tem- 
perature of melting ice, and T 0 the height of the temperature of melting ice above 
the point of absolute cold, as already stated. 
Then we have Nk=^-° . (41 a.) 
0 
According to these data, the equation of the isothermal curve of air for any tem- 
perature T is 
PV=P„V,.'^ =Nk(T+T„) (42.) 
The thermo-dynamic functions are — 
for quantities of actual heat, F=hyp. logQ+N hyp. logV ; 
for temperatures, d>=feF+constant=K v {hyp. log (T-f-T 0 )+N hyp. log V} ^ 
= K v hyp. log (T+T.) . hyp. log V ; 
(42 a.) 
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