in Fluids. 369 



Why should we not suppose that the Heat generated 

 by a ray of light, which, entering a mass of cold water, 

 accidentally meets with an infinitely small particle of any 

 solid and opaque substance which happens to be floating 

 in the liquid, and is absorbed by it, is not just as intense 

 as that generated in the focus of the most powerful burn- 

 ing mirror or lens? 



Mr. Senebier has given us an account of a great num- 



o o 



ber of interesting experiments on the effects produced 

 on different bodies by exposure to the direct rays of the 

 sun; but why may we not attribute all those effects to 

 the intense local Heat, generated by the light absorbed 

 by the infinitely small, and, if I may use the expression, 

 insulated particles of the bodies which were found to 

 be affected by it ? 



The surface of wood of various kinds was turned 

 brown. The same appearances might be produced in a 

 shorter time by the rays which proceed from a red-hot 

 iron, which change the surface of the wood to an imper- 

 fect coal. But were not the surfaces of the woods which 







were turned brown by the light of the sun in Mr. Sene- 

 bier's experiments changed to an imperfect coal ? And 

 is it possible for a Heat less intense than that of incandes- 

 cence to produce that effect ? 



Among the many facts that might be adduced to prove 

 that the most intense Heat may, and frequently does ex- 

 ist where we should not expect to find it, the following 

 appears to me to be very striking and convincing. It is, 

 I believe, generally imagined that the intensity of the 

 heat generated in the combustion of fuel is much less in 

 a small fire than in a great one ; but there is reason to 

 think that this is an erroneous opinion, founded on ap- 

 pearances that are not conclusive ; at least, it is certain 



VOL. I. 24 



