NATURAL PHILOSOPHY. 145 



material universe, or would regard it as suggesting a possible and con- 

 cievable, rather than a probable, mode of counteracting the constant 

 dispersion of heat from its existing centers. He has not, I think, 

 attempted to work out the consequences of the hypothesis as applied 

 to light, to which it must, I conceive, be necessarily considered 

 applicable if it be so to heat. In such case the foci of the reflected 

 heat would be coincident with those of the reflected light, proceeding 

 originally from the same luminous bodies. These foci would thus 

 become Visible as the images of stars ; so that the apparent number 

 of stars would be constantly increasing with the increasing number 

 of images of each star produced by successive reflexions. This will 

 scarcely be considered the actual order of nature. It would be easy 

 to trace other consequences of the application of this hypothesis to 

 light ; but I would at present merely state that my own convictions 

 entirely coincide with those of Prof. Thomson. 



In the year 1824, M. Carnot, of Paris, published a pamphlet entitled 

 Reflexions sur la puissance motrice du feu, which contains ideas, 

 (ciearly expressed) which have long been current, and still maintain 

 authority in some minds. This person advanced that in every fire 

 machine the labor effected is due simply to the passage of heat through 

 the moving power. The imponderable fluid acted somewhat like the 

 water which feeds an hydraulic wheel, and whose motive power de- 

 pends upon the difference of the level whence the water flows. As 

 after having produced its effects the water may be found in the same 

 quantity below as above the wheel, so, notwithstanding the fall of the 

 temperature occasioned by its diffusion, the caloric was said to exist 

 without loss when it came out of the fire machine. In reasoning in 

 this manner about the steam-engine, the boiler was compared to the 

 mill-dam basin, and the condenser represented after a fashion by the 

 lower basin. To complete the analogy, the word " fall" was employed 

 to express the passage of the heat from the boiler to the condenser, 

 and the height of this " fall" corresponded to the differences of tem- 

 perature. The greater was this difference or height of the fall, meas- 

 ured according to the degrees of the thermometric scale, the greater 

 was the amount of heat which passed in the same time, and the more 

 powerful was the machine. To submit this theory to a rigorous veri- 

 fication, it would have been necessary exactly to measure the quanti- 

 ties of heat really contained in the steam before and after it had per- 

 formed its functions, and to see if in truth the equality was maintained. 

 At that date an experiment of such great precision could not well be 

 made. They contented themselves w T ith reasoning a priori. And yet, 

 if they had only thought of a very common phenomenon : caloric de- 

 veloped by percussion, they would have seen its weakness. The phil- 

 osophical impossibility of the truth of this theory is escaped in a new 

 theory, by considering the intervention of heat from another point of 

 view. In the new theory, the quantity of heat communicated to the 

 boiler, and which from that moment belongs to the machine, is not 

 kept in toto in a state of caloric ; a portion instantly disappears, and in 

 its place they receive an equivalent quantity of motive power. This 



