268 Of the Propagation of Heat 



to swim on the Surface of the hot Water, — The melting 

 of Ice by Water standing on its Surface can be accounted 

 for^ even on the supposition that Water is a perfect Non- 

 conductor of Heat. — According to the assumed Hypothe- 

 sis^ Water only eight Degrees of Fahrenheit' s Scale above 

 the freezing Pointy or at the Temperature of 40°, ought to 

 melt as much ice, in any given Time, when standing on its 

 Surface, as an equal Volume of that Fluid at any higher 

 Temperature, even were it boiling hot. — This remarkable 

 Fact is proved by a great Variety of decisive Experiments. 

 — Water at the Temperature of ^\° is found to melt even 

 MORE Ice, when standing on its Surface, than boiling-hot 

 Water. — The Results of all these Experiments tend to 

 prove that Water is, in fact, a perfect Non-conductor of 

 Heat ; or that Heat is propagated in -it merely in conse- 

 quence of the Motions it occasions among the insulated or 

 solitary Particles of that Fluid, which, among themselves, 

 have no CommMnication or Intercourse whatever in this 

 Operation. — The Discovery of this Fact opens to our View 

 one of the grandest and most interesting Scenes in the Econ- 

 omy of Nature. 



AS the particles of water, as also of all other Fluids, 

 are infinitely too small to be seen by human eyes, 

 their motions must of course be imperceptible by us ; 

 but we are frequently enabled to judge with the utmost 

 certainty of the motions of invisible Fluids by the mo- 

 tions they occasion in visible bodies. Air is an invisible 

 Fluid, but we acquire very just notions of the motions 

 in air by the dust and other light bodies which are carried 

 along with it in its motions. Nobody who has ever seen 

 a whirlwind sweep over the surface of a ploughed field 

 in dry weather can have any doubt respecting the nature 



