



10 RADIANT HEAT. 



(2.) The coated vessel had its cooling in all cases retarded ; and in 



this order — 



Insiile. Outside. 



Least retarded black black. 



bright black. 



black bright. 



Most retarded bright bright. 



II. In air : both vessels in all instances had their cooling retarded 

 by the cases. 



Mr. Fox also found the boiling of water in a bright vessel be/ore a 

 fire accelerated nearly doubly by a case blackened externally. 



He considers the results inexplicable, except on the hypothesis of 

 an attraction between matter and heat. 



Mr. Fox has also communicated to me in manuscript an account of 

 some further experiments of the same kind on iron raised to a red 

 heat, but which, nevertheless, are of such a nature as properly to 

 come under this division of the subject. 



The precise temperature to which the iron was raised in each 

 experiment was estimated by the remarkable cessation of its action 

 on a magnetic needle at a certain stage of- incandescence. 



The iron was enclosed in tin cases of two different sizes, within 

 w T hich the air could be exhausted, the inside being either plain or 

 coated with lamp-black. 



The whole was immersed in Ivater, and the temperature communi- 

 cated to the water in a given time noted. After observation the iron 

 was plunged in water, and the residual heat thus communicated to 

 the water noted. 



The general results were, that in the smaller case the cooling was 

 more rapid than in the larger; and in either the internal coating accel- 

 erated., the cooling; in no case was any material difference produced 

 by exhausting the air. 



10.) Dr. Ritchie (Ed/in. Phil. Journal, xxii, p. 281,) has shown that 

 when a hot non-luminous body is placed between the two bulbs of a 

 differential thermometer, blown out very large and thin, and both 

 remaining plain, the liquid is stationary; the outside half of one being 

 coated with black, the liquid sinks from that side. 



Hence he infers that the coating has here stopped the heat, which 

 otherwise radiates freely through the very thin glass. 



He varied the experiment by using portions of glass blown thin as 

 screens over an aperture: when blackened in a flame or coated with 

 silver leaf they intercepted heat; when transparent, not. That this 

 was not from increase of thickness was shown by using three thick- 

 nesses transparent, then removing the middle one, and blackening 

 the inner surface of the others. 



He explains the subject by the theory of material caloric and mu- 

 tual repulsion of its particles. 



The same author in another paper (Ann. of Phil., 2d series, xii, 

 123.) gives a variation of the experiment: the hot body is placed 

 between two large and very thin bulbs; one of the hemispheres of 



