416 
ARTICLE XV. 
On the Cause of the Differences observed in the Absorbing Powers 
of Polished and of Striated Metallic Plates, and on the appli- 
cation of these Principles to the Improvement of Calorific Re- 
flectors. By M. Me wont. 
[-tnnales de Chimie et de Physique, 3me Série, vol. i. p. 861. March 1841.] 
In my last memoir* I often treated of plates whose temperature 
became gradually raised in consequence of their power of ab- 
sorbing calorific radiations. Under this head I particularly 
pointed out, that metals, and other substances capable of being 
made smooth and shining, were yet frequently so prepared as to 
present dead and completely unpolished surfaces. 
This was an essential condition in our experiments; for it 
was necessary to distinguish between the dispersion and reflec- 
tion, properly so called, in order to follow out, with any chance 
of success, the objects we then had in view. If, instead of using 
exclusively plates that are dead and uneven in surface, we 
experiment’ sometimes with polished and sometimes with un- 
polished surfaces, the calorific absorptions, compared with the 
nature of the plates, afford very curious results, of which we 
shall give a rapid sketch. 
A disc of brass, the surface of which is yet rough and granu- 
lar, becomes more strongly heated under the action of calorific 
radiation than a well-polished disc of the same metal. On the 
other hand, a metallic vessel of a rough surface, filled with hot 
water, cools more rapidly than a vessel made of burnished metal. 
These experiments have induced many experimental philoso- 
phers to admit that minute points and asperities in the surfaces 
of bodies increase both their absorbing and emissive powers. I 
have already endeavoured to prove, in a note communicated to 
the Academy}, that the emissive power of bodies does not de- 
pend on the degree of polish or of roughness communicated to 
their surfaces. 
({* Published in the Annales de Chimie et de Physique, vol. xxv. p. 337, for 
Dec. 1840. A traaslation of this Memoir will appear in a future Part.—Eb. ] 
| See Comptes Rendus des Séances de l’ Académie des Sciences, année 1838. 
