380 Of the Propagation of Heat 



steam, yet, from the extreme rapidity with which steam 

 condenses when in contact with cold water, it is evident 

 that it could not exist an instant under the circumstances 

 here supposed. Indeed, we have direct proofs that steam 

 cannot exist under such circumstances, by what is found 

 to happen when large masses of iron or steel, raised to 

 a most intense heat, in a blast furnace, are suddenly 

 plunged into cold water by smiths, in tempering edge- 

 tools ; for these masses of red-hot metal may be dis- 

 tinctly seen to be in actual contact with the cold water, 

 and did not a part of the water which is decomposed 

 by the hot iron make its escape in the form of inflam- 

 mable air, it is not probable that there would be any 

 visible appearance from which the formation of steam 

 could be suspected. 



Hence we see the possibility of the existence of in- 

 tense Heat in the midst of a mass of cold water, or of 

 any other transparent liquid, without producing any 

 visible effects, or leaving behind it any traces by which 

 its existence could be suspected. 



Let us now consider a case in which this intense Heat, 

 though perfectly imperceptible on account of the extreme 

 minuteness of the particles of matter in which it exists, 

 is capable, nevertheless, of producing very visible effects. 

 Let us suppose a solution of nitro-muriate of gold in 

 water to be exposed to the action of the sun's rays. If 

 this solution were perfectly transparent, no Heat could 

 possibly be generated in it by light ; but as it is not so. 

 Heat, in the highest degree of intensity, must necessarily 

 be generated by those opaque particles (of the oxyd of 

 gold) by which it is stopped. Now as gold is a very 

 heavy substance, it is evident that it must be reduced to 

 extremely small particles in order that, when changed to 



