474 M. Regnault's Researches upon the 



quantities of heat were dependent only on the initial and final 

 conditions of temperature and of pressure, and that they were 

 independent of the intermediate circumstances through which 

 the fluid had passed. In 1824, Camot published, under the 

 title of Rejleocions sur la Puissance Motrice du Feu, a work which 

 did not in the first instance attract much attention, and in which 

 he assumed as a principle that the motive power produced in a 

 steam-engine is due to the passage of heat from its source to the 

 colder condenser by which it is finally collected. M. Clapeyron 

 has developed the hypothesis of Carnot mathematically, and he 

 has shown that the quantities of heat' gained or lost by any one 

 gas does not depend solely upon its initial state and its final 

 state, but likewise upon the intermediate states through which 

 it passes. 



Within the last few years, the mechanical theory of heat has 

 met with more favourable consideration, and at the present 

 moment occupies the attention of a great number of mathemati- 

 cians. But an important modification has been made in the 

 px'inciple of Camot ; it has been assumed that heat may be con- 

 verted into mechanical work, and reciprocally that mechanical 

 work may be converted into heat. According to Carnot's theory, 

 the quantity of heat possessed by the elastic fluid at its entrance 

 into the steam-engine is found undiminished in the elastic fluid 

 which is discharged from it, or in the condenser ; the mechanical 

 work being produced solely by the passage of heat from the 

 boiler to the condenser in traversing the engine. According to 

 the new theory, the whole of this quantity of heat does not 

 remain in the state of heat ; a portion of it disappears during 

 the passage through the engine, and the motive work produced 

 is in all cases proportional to the quantity of heat lost. Thus in a 

 steam-engine, with or without condensation, working or not work- 

 ing expansively, the mechanical work is proportional to the difi*er- 

 ence between .the quantity of heat which the vapour possesses at 

 its entrance into the engine, and that which it possesses at its 

 discharge, or at the moment when it is condensed. According 

 to this theory, to obtain from the same quantity of heat the 

 maximum mechanical eficct, an arrangement should be adopted 

 in which that loss of heat should be as great as possible, that is 

 to say, the elastic force which the vapour retains at the moment 

 when it enters the condenser should be as small as possible. 

 But in every case referring to the steam-engine, the quantity of 

 heat rendered available for the mechanical eficct would only be 

 a very small fraction of that which it is necessary to communi- 

 cate to the boiler. In a high-pressure engine without a condenser, 

 into which the vapour enters under a pressure of five atmospheres 

 and escapes under the ordinary atmospheric pressure, the quan- 



