CONDUCTION AND RADIATION. 



arc not absolutely cold, but have a "proper heat" independent of the 

 sun and of the planets. If there were not such a heat, the cold of the 

 polar regions would be much more intense than it is, and the alterna- 

 tions of cold and warmth, arising from the influence of the sun, wor.M 

 be far more extreme and sudden than we find them. As the cause of 

 this heat in the planetary spaces, he assigns the radiation of the innu- 

 merable stars which are scattered through the universe. 



Fourier says, 18 "We conclude from these various remarks, and 

 principally from the mathematical examination of the question," that 

 this is so. I am not aware that the mathematical calculation which 

 bears peculiarly upon this point has anywhere been published. But 

 it is worth notice, that Svauberg has been led 19 to the opinion of the 

 same temperature in these spaces which Fourier had adopted (50 cen- 

 tigrade below zero), by an entirely different course of reasoning, 

 founded on the relation of the atmosphere to heat. 



In speaking of this subject, I have been led to notice incomplete 

 and perhaps doubtful applications of the mathematical doctrine of con- 

 duction and radiation. But this may at least serve to show that Ther- 

 motics is a science, which, like Mechanics, is to be established by 

 experiments on masses capable of manipulation, but which, like that, 

 has for its most important office the solution of geological and cosmo- 

 logical problems. I now return to the further progress of our thermo- 

 tical knowledge. 



Sect. 5. Correction of JTcu'tons Law of Cooling. 



lu speaking of the establishment of Newton's assumption, that the 

 temperature communicated is proportional to the excess of tempera- 

 ture, we stated that it was approximately verified, and afterwards cor- 

 rected (chap, i., sect. 1.), This correction was the result of the re- 

 searches 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 laborious experiment and sagacious induction. They experimented 

 through a very great range of temperature (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 tempera- 

 tures. They removed the effect of the surrounding medium, by 

 making their experiments in a vacuum. They selected with great 



5 J/'wi. List, torn, vii. p. 581. 19 Berzel. Jahrcs Bcr'u-ht. xi. p. 50. 



