1 82 Reflections on Heat. 



If the results of these experiments do not furnish a 

 conclusive proof of the radiation from all bodies, and 

 that it is by means of these radiations from surrounding 

 objects that the temperature of a given body is changed, 

 they certainly lend to this conjecture a great degree of 

 probability. 



Several other similar experiments were undertaken in 

 order to throw light on this point, and results were in- 

 variably obtained which tended to confirm the hypothe- 

 sis in question. 



Of all known bodies the metals are the most opaque, 

 and it appears that they are so to an equal degree ; it 

 appears also that a naked metallic surface, or one that is 

 free from all dirt, is always polished in spite of those 

 irregularities of form by which the brilliancy of its metal- 

 lic lustre is broken up and apparently diminished. If 

 these conjectures are well founded, we may conclude that 

 all metals are equally competent to reflect from their 

 surfaces the rays that impinge upon them ; and if ob- 

 jects are heated and cooled by rays from surrounding 

 objects, we might conclude not only that of all known 

 bodies the metals ought to acquire heat or become cold 

 the least rapidly, but also that they ought to acquire 

 heat or become cold with the same degree of difficulty 

 or rapidity. 



To put these suppositions to the test of experiment, 

 I procured several cylindrical vessels, of the same form 

 and dimensions but of different metals, and I found 

 that they did indeed all cool or acquire heat in the 

 same time. There were vessels of brass, tin, lead, and 

 others covered with thin coatings of gold and silver ; 

 each vessel was four inches in diameter and four inches 

 high, and when filled with boiling water and exposed, in 



