142 Experimental Investigations 



same form and dimensions, which is smooth or well 

 polished. 



This reasoning appears to me to be just, and, if I 

 am not deceived, the conclusions which may be drawn 

 from the facts in question, well confirmed by experi- 

 ment, ought to be considered as demonstrative. I 

 have taken every possible care to establish these facts ; 

 and the results of all my experiments have constantly 

 shown that more or less perfect polish, or the greater or 

 less brightness of the surface of a metallic vessel, does 

 not sensibly influence the time of its cooling. 



I took two equal vessels of brass, and polished the 

 external surface of one of them as highly as possible ; 

 and I destroyed the polish of the other by rubbing it 

 in all directions with coarse emery. When these two 

 vessels were filled with hot water, I did not find that 

 the unpolished vessel employed more or less time in 

 cooling than that which was polished. 



I was careful to wash the surface of the unpolished 

 vessel effectually with water, before the experiment ; as 

 I knew that if I did not take the precaution of remov- 

 ing all the dirt which might be lodged in the asperities 

 of the surface, the presence of these small foreign bod- 

 ies would influence the result of the experiment in a 

 sensible manner. 



We ought carefully to distinguish those surfaces 

 which appear unpolished to our eyes, but which in 

 fact are not so, from those which reflect little or no 

 light. 



It is more than probable that the surface of a metal 

 is always polished, and even always equally so in all the 

 cases wherein the metal is naked and clear and clean, 

 notwithstanding all the mechanical means which may 



