24:2 RECENT PROGRESS IN RELATION TO THE THEORY OF HEAT. 



oriijin, and consequently tlie connection wliicli it has with the sources previously 

 spoken of is suflicicntly established. 



It remains for me to show how the Voltaic circuit realizes the highest tempera- 

 ture known. AVe attach to the extremities of our two copper wires cylindrical 

 pieces of charcoal ; we then bring these cylinders into c<intact with one another. 

 The circuit is now closed. If we separate these two }iieces of charcoal, a mass 

 of dazzling light tills the interval between them and re-establishes the continuity 

 of the circuit. What is this light, which has received the name of the Voltaic 

 arch ? It is a volume of incandescent particles of charcoal, rfvhich acts in like 

 manner with the platina wire of the preceding experiment. This mass of par- 

 ticles is vehemently heated by the ])assage of the cuiTcnt. In order that its 

 enormous temperature mav be appreciated, we project it on a tablet by means of 

 lenses, having first enclosed it in a suitable box, that the eyes of the spectators 

 may be sheltered from its blinding brightness. By this expedient, we are enabled 

 to view all the details of the Voltaic arch. On the tablet we may see the reversed 

 image of the sticks of charcoal, themselves heated to white-red, as well as that 

 of liie arch, which appears as a violet flame. Let us place a sheet of platina in 

 this thimc ; it melts rapidly, and the fused platina collects iu a sparkling globule 

 on one of the pieces of charcoal. Thus, the heat is at least as strong as in the 

 furnace which, an instant ago, we heated by a chemical process. But it is much 

 stronger, and if we placed a diamond instead of jdatina in the Voltaic arch, it 

 would be seen to become soft and begin to melt. AVere we to conduct this opera- 

 tion in a vacuum, the vapor of the diamond and that of the charcoal of the 

 api>aratus would be deposited on the walls of the vase. This experiment Avas 

 made for the first time by Despretz, at the Sorbonne, with a battery of adequate 

 power. 



The sources of heat which I Ikivc thus far noticed are at the disposal of man, 

 who can regulate them at his pleasure ; these arc arfiticial sources. It remains 

 to speak of the natural sources — of those whose power the Creator has regulated, 

 in order to constitute the universal harmony of natvire. 



It is impossible to explain iu this short discourse, by what admirable laws heat 

 is incessantly generated by animals. It suflices to recall the fact that this heat 

 has a cheuiical origin, in order to comprehend that it is referable to the same fun- 

 damental principle with the others. In effect, the carbon and hydrogen furnished 

 by our aliments are placed in presence of the atmospheric oxygen by the act of 

 respiration, and their chemical combination is etl'ected in the blood, attended Avith 

 the customary disengagement of heat. I should add, however, that animals 

 further create heat by another process purely mechanical. When a man, for 

 instance, goes down stairs, his body is displaced and falls, as it were, from a 

 small height ; he displaces it anew, again falls, and continues doing so. Now, 

 each of these little descents creates heat, like the fall of every heavy body which 

 does not rebound. One of our most distinguished savants, M. Hirn de Colmar, 

 has succeeded in measuring the heat thus produced, and finds that it very com- 

 petently satisfies the general law. 



I might also speak of the heat disengaged by vegetables, at certain epochs, 

 when their organs are the theatre of intense chemical reactions ; at the same time, 

 I should say that it is much rather their rc)le to consume heat than to produce it, 

 and that in this the functions of vegetable life are made to compensate those of 

 animal life. But I am about to transport my audience into other regions, in 

 essaying to lift a corner of the veil which renders them so mysterious. 



The grand and most wonderful source of heat is the sun. The genius of man, 

 bursting at a bound its terrestrial shackles, has long since overleaped the dis- 

 tance which separates us from that marvellous luminary. It has measured, it has 

 weighed it, and we are to-day very remote from the time when men bowed in awci 

 before it as before a divinitv. Taking as a jiuide the observations conducted b}^ 



