The Rev. J. M. Heath on Thermodynamics. 421 



itself between them according to their avidity and their number 

 of equivalents; the mode according to which this division is 

 effected is expressed with satisfactory exactitude by M. Guld- 

 berg's theoretical formula*. 



LX. On Thermodynamics. By the Rev. J. M. Heath f. 



THE variations in the temperature of a body which occur 

 during its expansion and condensation had long been re- 

 garded as a problem in physics, to be determined by purely 

 experimental and inductive methods. Until comparatively quite 

 recent times it was held that the cold produced in rapidly ex- 

 panded air, and the permanent cold in the permanently rarefied 

 air of the upper regions of the atmosphere, were alike caused by 

 the rarefaction itself, and that the capacity of a body for heat 

 increased with its rarity. This doctrine is now abandoned ; and 

 it is now held that the energy or quantity of action of a force 

 which causes a condensation is the cause and the measure of the 

 evolution of heat in the body w T hich is observed to follow. 



From the moment when this doctrine was regarded as esta- 

 blished by a sufficiently probable induction to entitle it to be 

 made the basis of future inquiry, the science, thenceforth to be 

 called the Science of Thermodynamics, had passed from the cate- 

 gory of inductive sciences and had virtually become a branch of 

 dynamics, the business of which is the deduction of the conse- 

 quences of previously admitted first principles in their applica- 

 tion to particular cases. The exhibition of heat was now a con- 

 sequence of the action of force; and it was apprehended that its 

 production would be found to follow the same laws as connect 

 the vis viva of a system of particles with the quantity of action 

 which generates it. Now the quantity of vis viva which a given 

 energy will generate is perfectly well known. It only remained, 

 therefore, to ascertain whether the empirical law connecting the 

 quantity of heat evolved in a given condensation with the con- 



* [It is probable that, if the author has considered himself able thus to 

 generalize conclusions from observations which only comprise so small a 

 number of cases, it is because these conclusions seemed to him justified by the 

 very great number of other experiments which he has made and intends to 

 publish shortly. Without that they would not be sufficiently proved. As we 

 have already remarked in a preceding note, the ratio according to which soda 

 divides itself between sulphuric acid on the one side, and nitric and hydro- 

 chloric acids on the other, might be explained simply by the tendency of the 

 first acid to form a bisulphate, without its being necessary to introduce a 

 difference of energy or avidity. In order, however, to be able to form a judg- 

 ment on this theorv, we must wait for the rest of the memoirs announced 

 by M. Thomseii.— C. M.] 



t Communicated by the Author. 



