KNOCLAUCU OX RADIANT HEAT. 433 



The same might be said of the luminous rays of platinum at a 

 white, yellow and red heat. 



In the previous details I have purposely avoided all theoretical 

 remarks an the nature of the phaenomena of heat, so as not to 

 view the facts, which are the only permanent parts of science, 

 from the perishable basis of a hypothesis. I shall not even now 

 enter upon speculations of this kind, which can only lead to the 

 desired object when combined with a fundamental mathematical 

 treatment. Perhaps the observations contained in these essays 

 may contribute to establish greater unity of principle in the 

 theory of heat, in which greater discrepancy of theoretical views 

 has prevailed than in any other branch of physics. 



I shall therefore conclude this memoir by briefly summing up 

 the principal results which have been obtained from the experi- 

 ments detailed. 



1. There are two new means of deciding with certainty whether 

 any body transmits rays of heat or not. (See pp. 232, 236, 237.) 



2. The transmission of radiant heat by diathermanous bodies 

 has no direct relation to the temperature of its source, but 

 depends solely upon the propei'ties of the diathermanous sub- 

 stances, which are permeated by certain rays of heat in a greater 

 degree than by others, whether these are of a low or high tem- 

 perature. (See p. 203.) 



3. The absorption of radiant heat by a body, when the rays 

 permeating it are of the same uniform intensity, is perfectly in- 

 dependent of the temperature of its source, and is alone occa- 

 sioned by the nature of the absorbing body, which is more sus- 

 ceptible of some rays than of others. (P. 206 and 207.) 



4. A body becomes heated, within certain limits, in proportion 

 to its thickness, and in a degree which is greater the less it is 

 diathermanous to the rays transmitted to it. (P. 209-211.) 



5. Absorption and emission of heat correspond to each other 

 so far only as they are functions of one and the same body ; 

 and the nature of the rays of heat has no influence on it. 

 {P. 216 and 217.) 



6. The position advanced by Mclloni is confirmed, viz. that 

 scratching the surface of a body influences its power of radiating 

 heat merely so far as it modifies its density and hardness, and 



VOL. V, PART XIX. 2 G 



