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consequence of Prevost's theory of exchanges ; but if, on the other 

 hand, we do not admit that all the kinds of radiant light given out 

 by heated bodies possess this property, then in that case those facts 

 cannot be explained by Prevost's theory, but they will require a new 

 theory to account for them. 



This circumstance induces me to think that all the descriptions of 

 light radiated by heated bodies have the power of heating, more or 

 less, those bodies by which they are absorbed. Viewing the matter 

 in this light, I have constructed the following Table, in which the 

 logical consequences of Prevost's theory are stated in the first 

 column, while opposite these in the second column are detailed the 

 different experiments which they serve to explain. 



Table of the consequences of Prevost's theory, and the facts which 

 they explain. 



Consequences of Prevost's theory. 



The radiation of a thin plate or par- 

 ticle is equal to its absorption, and that 

 for every description of heat that is to 

 say, in quality as well as in quantity. 



Facts which these consequences explain. 



Rock-salt which absorbs little heat 

 of 212 F., gives out little ; while glass, 

 which absorbs much, gives out much. 



The heat radiated by rock-salt has 

 great difficulty in passing through a 

 screen of rock-salt the heat radiated 

 by glass in passing through a screen of 

 glass. 



Colourless glass, when heated, gives 

 out little light, opaque glass a great deal. 

 Red glass, which absorbs the greenish 

 rays, gives out greenish rays; while green 

 glass, which absorbs the red rays, gives 

 out red rays. 



When a plate of glass is coated on its 

 further side with lamp-black, its heat is 

 the same as lamp-black heat. 



All coloured glasses appear to lose 

 their colour in the fire, 

 f Metals radiate little, both of heat and 



Those opaque bodies which reflect 

 most, radiate least. Opaque bodies ge- 

 nerally give out the same kind of rays 

 at the same temperature : these words 

 also express the known fact. 



light. Table-salt, which is white for 

 heat of 212, radiates less than sugar, 

 which is black. When a black and white 

 china cup is heated in the fire and held 

 in the dark, the black of the pattern is 

 . more luminous than the white. 



