346 Mr. R. W. Fox on some Phaenomena of Heat. 



These results show ; 

 1st. That the times oi cooling differed but little, whether 

 bright surfaces were opposed to each other, or bright 

 and black ones alternately. 

 2dly. That when No. 1 was inclosed in a case externally 

 bright, its cooling was not thereby retarded, but rather 

 the reverse. 

 3dly. That when two more cases were added to the above, 

 No. 1. cooled more rapidly in vamo, even when all the 

 cases were bright,although they were, I think, together, 

 nearly equal to the former in their capacity for heat. 

 4thly. That the cooling of No. 1. iii vacuo was still further 



accelerated when the outermost case was black. 

 Sthly. That the cooling of No. 2. was retarded in every in- 

 stance by the addition of a case. 

 6thly. That when the outside of a case was black, and the 

 inside bright, the times of cooling of Nos. 1. and 2. in 

 air, and in vacuo, were not very widely different. 

 The fact last mentioned may, I think, be attributed to the 

 influence or resistance of the air included between the inner 

 vessels and the cases. In corroboration of this explanation, 

 I found that when No. 1. was placed in a bright case, and 

 hermetically soldered to it at its upper rim, so as to prevent 

 the escape of the intervening air, it cooled more slowly in vacuo 

 than it afterwards did with a perforation in the case which ad- 

 mitted of the included air being exhausted under the receiver; 

 the ratio of the former to the latter having been as I'l to I'O. 

 When No. 1. was put into the large outside case, used in 

 Experiment 5, it cooled more slowly in vacuo than it did in 

 a smaller bright case ; and when an intermediate one was 

 added, the cooling was accelerated thereby. 



The size of the glass receiver seemed also to affect the time 

 of cooling of the included body in vacuo, it having been re- 

 tarded when a larger receiver was employed. I therefore 

 infer that the results of experiments on the transmission of 

 heat without the intervention of air will always have some re- 

 lation to the distances of the bodies at different tempei'atures 

 from each other; and that those I have stated would have 

 been subject to modifications, not only from using a larger re- 

 ceiver, but also from a more perfect exhaustion of the air than 

 I could obtain. 



I also made various experiments on the rate at which bodies 

 Laving different surfaces were heated in close vessels sur- 

 rounded by steam, which kept them at an uniform tempera- 

 ture; and on the effects of heat, accompanied by light, on po- 

 lished and unpolished metals : — one of the latter description 

 I may briefly mention. My apparatus consisted of two cylin- 

 drical 



