2 THEORY OF HEAT. 







of Newton been confirmed : quod tarn paucis tarn multa prcestet 

 geometria gloriatur\ 



But whatever may be the range of mechanical theories, they 

 do not apply to the effects of heat. These make up a special 

 order of phenomena, which cannot be explained by the principles 

 of motion and equilibrium. We have for a long time been in 

 possession of ingenious instruments adapted to measure many 

 of these effects; valuable observations have been collected ; but 

 in this manner partial results only have become known, and 

 not the mathematical demonstration of the laws which include 

 them all. 



I have deduced these laws from prolonged study and at 

 tentive comparison of the facts known up to this time : all these 

 facts I have observed afresh in the course of several years with 

 the most exact instruments that have hitherto been used. 



To found the theory, it was in the first place necessary to 

 distinguish and define with precision the elementary properties 

 which determine the action of heat. I then perceived that all the 

 phenomena which depend on this action resolve themselves into 

 a very small number of general and simple facts ; whereby every 

 physical problem of this kind is brought back to an investiga 

 tion of mathematical analysis. From these general facts I have 

 concluded that to determine numerically the most varied move 

 ments of heat, it is sufficient to submit each substance to three 

 fundamental observations. Different bodies in fact do not possess 

 in the same degree the power to contain heat, to receive or transmit 

 it across their surfaces, nor to conduct it through the interior of 

 their masses. These are the three specific qualities which our 

 theory clearly distinguishes and shews how to measure. 



It is easy to judge how much these researches concern the 

 physical sciences and civil economy, and what may be their 

 influence on the progress of the arts which require the employ 

 ment and distribution of heat. They have also a necessary con 

 nection with the -system of the world, and their relations become 

 known when we consider the grand phenomena which take place 

 near the surface of the terrestrial globe. 



1 Phiiosophia naturalis principia mathematica. Auctoris prafatio ad lectorem. 

 Ac gloriatur geoinetria quod tarn paucis principiis aliunde petitis tarn multa 

 proestet. [A. F.] 



