586 
DB. J. P. JOULE Am) PBOFESSOK W. THOMSON ON 
Table VI. 
No_. of 
experiment. 
Proportions of 
mixtures. 
Temperature 
of bath. 
Thermal effect 
for air. 
Deduced thermal 
effect for pure COj. 
1 
Air. 
68-42 
00^. 
31-58 
^36 
O 
—88 
O 
— 4-51 
2 
89-16 
10-84 
7-36 
—-88 
-4-61 
3 
3-52 
96-48 
7-38 
-•88 
-4-46 
4 
62-5 
37-5 
7-41 
—88 
— 4-19 
5 
88-13 
11-87 
7-43 
—•88 
-3-98 
6 
97-46 
2-54 
7-61 
—88 
-3-89 
16 
1-83 
98-17 
35-6 
—75 
-3-44 
14 
67-7 
32-3 
49-7 
-- 7 
—3-04 
15 
87-77 
12-23 
49-76 
-• 7 
“2-77 
13 
0-83 
99-17 
54 
-•66 
-2-96 
10 
2-11 
97-89 
93-52 
—•51 
-2-19 
11 
56-78 
43-22 
91-26 
—•51 
—2-21 
12 
77-77 
22-23 
91-64 
—•51 
— 3-08 
17 
1-66 
98-34 
97-55 
-•49 
— 2-16 
1 2 3 4 5 
The agreement for each set of results at temperatures nearly agreeing (with one excep- 
tion, No. 12), shows that the assumption m : m ' : : 1 : *7 cannot be far wrong within our 
limits of temperature. 
[Beceived subsequently to tbe reading of the Paper.] 
Ajjjylication of the p'eceding results to deduce apijfoximately the- Equation of Elasticity 
for the gases experimented on. 
The “ equation of elasticity ” for any fluid is the most appropriate name for the equa- 
tion expressing the relation betAveen the pressure and the volume of any portion of the 
fluid. As this relation depends on the temperature, the equation expressing it invoh'es 
essentially three variables, AA^hich, as in our previous communications on this subject, we 
^all denote byy;, -r, t. Of these, p is the pressure in units of force per unit of area, 
V the volume of a unit mass of the fluid, and t the temperature according to the abso- 
lute thermodynamic system of thermometry Avhich Ave have proposed. As before, we 
shall still adopt a degree, or thermometric unit, agreeing approximately with the degree 
Centigrade of the air-thermometer ; according to which, as we haA'e demonstrated by 
experiment f , the value of t for the freezing-point is Avithin a feAV tenths of a degvee of 
273 ’7 (its A'alue at the standard boiling-point being, by definition of the Centigrade 
scale, 100° more than at the freezing-point). 
Instead of, as in our previous communications, taking v and t as independent variables, 
we shall now take^j and t‘, and we shall accordingly consider the object of the equation 
of elasticity as being to express v explicitly as a function of p and t. WhateA^er may be 
the relation betAveen these elements, the thermal effect, d^ (reckoned as positNe when 
it is a rise in temperature), produced by forcing the fluid in a continuous stream through 
a narrow passage or porous plug by an infinitely small difierence of pressures, ((p, Avill 
* PhilosopLical Transactions, 1854, p. 350. t Ibid. p. 352. 
