234 GREAT MEN OF SCIENCE 



importance for the steam engine and all other heat engines 

 since constructed; also, already without the further know- 

 ledge contributed by Robert Mayer and then Clausius, 

 Carnot is able, at the conclusion of his essay, to add a per- 

 tinent discussion concerning possible improvements in the 

 steam engine as a result of his work. We may also mention 

 that, in addition, he developed very finely thought-out 

 conclusions as regards the heat properties of gases. 



Carnot's ideas are well linked together and with ex- 

 perience; nevertheless this connection is not completely 

 rounded off. Carnot feels this himself, and he notes at 

 several points certain open questions. These particularly 

 relate to the assumption of the invariability in quantity of 

 heat, which Carnot takes for granted, but not without re- 

 markingi that this assumption, which is the 'foundation of 

 the whole theory of heat' nevertheless still 'needs attentive 

 investigation,' since 'several facts of experience seem to be 

 almost inexplicable according to the theory in its present 

 state.' According to this assumption, made at that time for 

 want of better knowledge, the quantity of heat leaving the 

 boiler with the steam would in the steam engine be given up 

 in undiminished quantity to the condenser, though reduced 

 to a lower temperature, just as the water in a turbine does 

 not diminish in amount, but does its work merely by falling 

 in level. This is not correct, as Robert Mayer showed in 

 1842.2 The heat does become less; it is partly transformed 

 into work. It later appeared from Carnot's posthumous 

 papers^ that he himself had already arrived at a recognition 



^ Footnote to Carnot's essay. 



2 Two years before Carnot's publication, the invariability of quantities 

 of heat had been successfully maintained in the large work of Founer, 

 Thiorie de la Chaleur, which appeared in 1822. This work, however, 

 which is distinguished by wonderful clarity and great mathematical 

 power, only deals with processes of heat conduction, for which the invar- 

 iability is also sufficiently true. 



3 These were first published in the year 1878 by his brother, as ap- 

 pendix to a second edition of the essay Reflexions sur la puissance motrice 

 du feu. 



