238 EECENT PEOGRESS IN RELATION TO THE THEORY OF HEAT. 



lislied — one at tlie bottom, the other 60 centimetres higher up. By regulating the 

 heat, the water of the latter region is maintained at a temperature a little below 

 103 degrees, and therefore cannot boil ; but if the strata of the bottom are raised 

 to 105 degrees, they are thrown into ebullition, and the steam raises the middle 

 stratum. This is immediately reduced to vapor, and the erruption takes place. 

 The mixture of water and steam falls back into the basin, re-enters the tube, and 

 a certain interval elapses before the fires can re-establish the temperatures requi- 

 site for a new eiTuption. 



In thus presenting to my auditors a view of some of the recent researches of 

 physicists, I have endeavored to indicate the philosophic tendency of those 

 researches. They lead us to presage new advances which will draw closer the 

 bonds which science has discovered between the various forces of nature. Is it 

 enough for us to picture to ourselves the mechanism of phenomena by the help 

 of ingenious hypotheses ? Hypotheses are useful to the physicist for the dis- 

 covery of the nuinerical laws, which reveal to us the harmony of the imiverse ; 

 they do not suffice for the philosopher who wishes to ascend higher in the search 

 for causes. But to the data of experimental science it is necessary to join prin- 

 ciples of a wholly other order, the geim of which has been implanted in our souls 

 by the Creator. The origin and essence of natural forces are questions of phi- 

 losopliy whose solution, if it is possible, exacts all the powers of investigation 

 of which the human mind is capable. 



THE PRINCIPAL SOURCES OF HEAT.* 



In selecting as the subject of this discourse the principal sources of Jicaf, I 

 have proposed to give a very simple example of the connection which exists 

 between natural phenomena, even those to which we might, if we contented our- 

 selves with a superficial examination, deny a community of origin. But when 

 mental practice has habituated us to observe what surrounds us, and to draw gen- 

 eral conclusions from our observations, when we have learned to read, in some 

 sort, the gr?at book of nature, we hesitate no longer to recognize the connec- 

 tions which escaped us at first, and we seek an expression for those connections ; 

 when we have found that expression, we have constructed a physical theory. 

 The theory which will serve me to show the connection of the sources of heat 

 is very recent ; it is alluring from its very simplicity. But being a work purely 

 human, it is but a rough portraiture, a pale reflection of the grand unity which 

 reigns throughout nature. All the merit of this theory consists in its being bet- 

 ter than those which preceded it, and in seeming to approach nearer to the truth. 

 This must justifj^ us in adopting it. 



Let us understand, then, the limits to which we are restricted ; as far as con- 

 cerns us at present, to explain a phenomenon is to show the connection which 

 exists between that phenomenon and a general principle whicli is the expression 

 of a fact more simple than experiment has revealed to us. I shall commence by 

 establishing the fundamental principle on which I propose to sustain myself. 



When a ball of ivory falls on a horizontal plane of marble, it rebounds and 

 returns almost to its point of departure. Repeat the experiment, by replacing 

 the ivory with lead, and the ball will rise to a less height in rebounding ; but 

 now it will grow warm, which was not the case with the ball of ivory. Cause 

 soft bodies or liquids to fall ; these will no longer rebomid, and if we measure 

 their temperature we shall find the heat created by the impact to be greater than 

 in the previous instance. 



It is now known that every pound of every ponderous body, which loses its 

 velocity by falling from a height of about 720 feet, and which does not rebound, 

 disenages a quantity of heat capable of raising by one degree the tempcraturo 



* Conf6renco de M. Cazin. "Soiree scientifique de Chartres." Revue des cours scientifiqucs 

 de la France, Sfc, July, 1867. 



