500 Radiation ofRoufrh and Polished Surfaces. 



variations sometimes exceed the ratio of two to one. Hence 

 a deduction has been drawn, that the observed increase is owing 

 to those inequalities which have been impressed upon the vessel, 

 and that, consequently, the superficial asperities of bodies have 

 the property of facilitating the exit of the heat which they con- 

 tain. I beg the honour of communicating to the Academy the 

 abstract of a series of researches, whence it seems decidedly to 

 follow that this proposition is wholly erroneous ; so that if the 

 superficial layers clearly and decidedly contribute to make a 

 difference in the quantity of heat emitted by a hot body, the 

 state of the surface has no part in the production of this phe- 

 nomenon. 



First, I must avow that, in spite of the authority of great 

 names, the influence of this polish in calorific emission, has al- 

 ways appeared to me very doubtful. It is said, the interior 

 heat experiences in quitting the body the same action of the 

 surface which it undergoes in penetrating it in the way of ra- 

 diation. Be ^it so. But why should these small shining j^- 

 cettes (facettes miroitantes ) which you produce by streaking 

 the polished plate, reflect interiorly less heat than the surface 

 uniformly polished? Take a vessel of copper, having two po- 

 lished sides slightly obscured by exposure to the air : make 

 with the graver on the one of these sides, a series of parallel 

 furrows ; the little furrows thus produced, will certainly be more 

 brilliant then the rest of the vessel, and, notwithstanding, the 

 furrowed surface will emit more heat than the smooth one. It 

 IS now nearly two years since I imparted this objection and 

 some other experiments of the same sort, to Messrs Bache, 

 Henry, and Locke, distinguished professors of physics from 

 the United States, who were then in Paris. Now, however, that 

 the question appears to me decided, I lay aside all indirect ob- 

 jections, and pass immediately to the exposition of results which 

 conduce directly to the proof of the alleged fact. 



I took a cubic vessel of copper, whose four faces were very 

 carefully formed ; externally, I soldered on its lower angles and 

 edges, grooves provided with springs, for the purpose of sup- 

 porting firmly against the vessel plates of two or three lines in 

 thickness ; and having afterwards procured two pairs of plates, 

 one pair of jet, and the other of ivory, I applied them to the 



