236 RECENT PROGRESS IN RELATION TO THE THEORY OF HEAT. 



the physicpl and natural sciences. Admirable as lias been its previous career, it 

 tas before it tbe most brilliant future. When our illustrious Ampere had divined 

 the connection which exists between magnetism and electricity, electrodynamics 

 was founded, and brilliant discoveries arose on every side. Our own o-eneration 

 nas 710 cause to envy its predecessor; to the former pertains the credit of the 

 development and application of thermodynamics. The formulas deduced from 

 this branch of science have undergone the test of experimental scrutiny, applied 

 by M. Regnault and other physicists ; those formulas have other tests to undergo, 

 by suggesting new experiments which had probably never been attempted without - 

 them. 



The scientific association of France will contribute to this progress by facili- 

 tating and stimulating research. In this spirit its committee of physics has 

 charged me with the study of the properties presented by saturated vapors when 

 they undergo expansion or compression, and the results obtained have been pub- 

 lished. Tlie creation of new apparatus has led to other researches. It is thus 

 that M. Hirn and myself have recently solved an important problem, respecting 

 Avliich theie hud not, to our knowdedge, been any previous ex[)eriniental infor- 

 mation. I may be permitted here to give a statement of that problem : '' A 

 vapor supersaturated with heat is suddenly expanded by producing an external 

 labor, without addition or subtraction of heat; what is the relation of the pressure 

 to the temperature during the expansion ?" There is an agreement between the 

 results we have reached and the principles of thermodynamics ; they prove that 

 the changes of volume in vapors are accompanied by a considerable internal 

 labor. 



The laws which govern the internal labor of bodies are of the highest importance 

 towards a knowledge of the constitution of matter, and yet those laws have been 

 scarcely so much as surmised. To this day, experiments have had for their 

 principal object the relations of heat and of external labor; it is from these exper- 

 iments that have been deduced the numerical data now in use. The experi- 

 ments relative to internal labor are more dithcult and more rare. We have had 

 recently the researches of M. Edluug, in Germany, on the thermic effects of the 

 traction of metals. The principal experiment, and which the author lias submit- 

 ted to careful study, is the following : Along a stout piece of vertical wood is 

 arranged a bar of metal terminated below by a ring, and firmly fixed by its 

 upper extremity. Through the ring a strong iron lever is passed, one extremity of 

 which rests on an^axis attached to the piece of wood at a short distance from the 

 ring, and the other extremity bears a basin at nine times that distance from the 

 ring. When we place on this basin a weight of GO kilograms, we exert on the 

 bar of metal a traction of about 600 kilograms, the lever being of the second 

 order. A thermo-electric battery has one of its faces applied against the bar, and 

 a galvanometer shows the depression of the temperature. Let us now gradually 

 lift the weight hi order to allow the bar to return to its primitive length ; the 

 galvanometer indicates a corresponding elevation of temperature. Finally, if 

 we suddenly remove the weight, there is again an elevation of temperature ; 

 but this time greater than before. 



How is this phenomenon to be explained? Let us consider the bar as elon- 

 gated by the external traction; its particles have taken such positions that the 

 internal forces form an equilibrium to the external forces. If we suppress the 

 latter, the body resumes its original volume through the effect of the internal 

 forces, and there is an internal labor expended ; there is a manifestation, there- 

 fore, within the body itself of a quantity of heat proportional to that labor, and, 

 consequently, a spontaneous elevation of temperature ; it is here taken for granted 

 that the calorific action of neighboring bodies may be overlooked. 



In place of suddenly suppressing the traction, let us allow the molecular forces 

 to restore the body, little by little, to its original volume, by gradually dimin- 

 ishing the force oi' traction. The external labor thus produced will correspond 



