538 HISTORY OF THERMOTICS. 



that Thermotics is a science, which, like Mechanics, 

 is to be established by experiments on masses capa- 

 ble of manipulation, but which, like that, has for its 

 most important office the solution of geological and 

 cosmological problems. I now return to the further 

 progress of our thermotical knowledge. 



Sect. 5. Correction of Newton's Law of Cooling. 



IN speaking of the establishment of Newton's as- 

 sumption, that the temperature communicated is 

 proportional to the excess of temperature, we stated 

 that it was approximately verified, and afterwards 

 corrected, (p. 520.) This correction was the result 

 of the researches of MM. Dulong and Petit in 1817, 

 and the researches by which they were led to the 

 true law, are an admirable example both of labor- 

 ious experiment and sagacious induction. They 

 experimented through a very great range of tem- 

 perature, (as high as two hundred and forty degrees, 

 centigrade,) which was necessary, because the inac- 

 curacy of Newton's law becomes considerable only 

 at high temperatures. They removed the effect of 

 the surrounding medium, by making their experi- 

 ments in a vacuum. They selected with great judg- 

 ment the conditions of their experiments and com- 

 parisons, making one quantity vary while the others 

 remained constant. In this manner they found, that 

 the quickness of cooling for a constant excess of 

 temperature, increases in geometrical progression, 



