NATURAL PHILOSOPHY. 147 



final conditions only were considered, the two experiments would seem 

 to be the same, and the cause of the difference of the caloric effects 

 produced in the two cases, would pass unperceived. But if inquiry 

 be made of available labor produced, it would be found to be consider- 

 able in the circumstances where the temperature fell, while in the 

 other case, it was null. When the capacity of the first vase is doubled 

 in volume, the side which withdraws, undergoes an effort which would 

 be capable of raising a weight placed outside of the furnace, while at 

 the moment the two reservoirs are placed in communication, the es- 

 cape of air can engender only currents of air, which die in the interior 

 of the reservoir, without transmitting anything outside. No experi- 

 ment could be made to demonstrate more clearly the close connection 

 existin^ between heat and the result of its transformation into mechan- 



o 



cal labor. 



In a recent communication to the French Academy, M. Regnault 

 continues the subject. In all fire machines heretofore employed, heat 

 acts through the medium of an elastic fluid, gas or vapor, saturated or 

 not saturated. This elastic fluid is only a vehicle to which heat is con- 

 fided, for it has need of a substratum wherein to fix itself, and without 

 which it would instantly escape in its radiating form ; consequently it 

 is necessary to ascertain the quantity of heat the different vehicles will 

 take or leave in passing from one to another temperature. This quan- 

 tity of heat, easily determined in solids and in liquids, may serve to 

 characterize the different bodies in nature, and it has been felicitouslv 



i 



named specific heat : water is in this regard characterized among all 

 other bodies in a very remarkable manner; it possesses (to use the 

 received phrase), the greatest capacity for heat ; i.e. it can contain in 

 the same weight a greater quantity of caloric than any other known 

 body in nature. Consequently, if any one had to distinguish water in 

 the midst of other liquids, all enclosed in- sealed bottles, it could be 

 discerned by this single characteristic : to raise its temperature ten, 

 twenty, thirty degrees, more heat, and consequently more fuel would 

 be required than for all the others. It is in consequence of its great 

 capacity for heat that water is so convenient to fill heating apparatus 

 in which the experimenter does r^ot wish to make a fire. If the feet- 

 warmers ladies place in their pews or carriages during the winter, 

 were filled with alcohol or oil, or mercury, they would complain of 

 the rapidity with which they cool, even more than they do now. It is 

 also partly to the greatness of this coefficient that the sea owes its 

 equality of temperature. Its mass taking a great deal of time to fill 

 with heat, is also very slow in dischargement, so that winter comes be- 

 fore its reheating is concluded, and reciprocally summer returns before 

 the cooling has made very great progress. The difference between 

 the capacities of solids and liquids for the " storing " of heat must, ac- 

 cording to all probability, also exist in gases, but as these may besides 

 be treated in two different ways, as they are forced, during the change 

 of temperature, to keep the same volume or the same pressure, there 

 are two different specific heats to be considered in each gas, namely, 

 specific heat under constant pressure, and specific heat under constant 



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