
CARNOT’S THEORY OF THE MOTIVE POWER OF HEAT. 565 
clusion, the actual methods of obtaining mechanical effect from heat are briefly 
examined with reference to their economy. 
I. On the values of pb derived by Carnot and Clapeyron from observations on Air, and on the 
Vapours of various liquids. 
43. In Carnot’s work, p. 80-82, the mean value of u between 0° and 1° is 
derived from the experiments of DeELARocHE and BERARD on the specific heat of 
gases, by a process approximately equivalent to the calculation of the value of 
10} Eon et 
lay 
°F 
of the values of u from observations on the vapours of alcohol and water; but a 
table given in M. CLapEyRon’s paper, of the values of » derived from the data 
supplied by various experiments with reference to the vapours of ether, alcohol, 
water, and oil of turpentine, at the respective boiling-points of these liquids, afford 
us the means of comparison through a more extensive range of temperature. In 
the cases of alcohol and water, these results ought of course to agree with those of 
Carnot. ‘There are, however, slight discrepancies which must be owing to the 
uncertainty of the experimental data.* In the following table, CarNovt’s results 
with reference to air, and CLAPEYRON’S results with reference to the four different 
liquids, are exhibited, and compared with the values of uw which have been given 
above (Table I.) for the same temperatures, as derived from REGNAULT’s observa- 
tions on the vapour of water. 
v a t : , 
* for the temperature 4°. There are also, in the same work, determinations 
Values of « de- 
duced from 
Regnault’s 
Observations. 
Names of the Media. Temperatures. Values of « Differences. 


Air, . 0°5 (Carnot) 4-377 4-960 
Sulphuric Ether, (Boiling point) 85°5 |(CLapzyron) 4° Eas 4:510 
Alcohol, . 78°8 4:030 
Water, : 4 | 3°337 
Essence of Turpentine, ; : 3449 




44. It may be observed that the discrepancies between the results founded on 
the experimental data supplied by the different observers with reference to water 
at the boiling-point, are greater than those which are presented between the re- 
sults deduced from any of the other liquids, and water at the other tempera- 
tures ; and we may therefore feel perfectly confident that the verification is com- 
* Thus, from Carnovt’s calculations, we find, in the case of alcohol, 4:035; and in the case of 
water, 3°648, instead of 3:963, and 3°658, which are CLApEYRon’s results in the same cases. 
VOL. XVI. PART V. 7G 
