366 Of the Propagation of Heat 



CHAPTER III. 



Probability that intense Heat frequently exists in the solitary 

 Particles of Fluids^ which neither the Feeling nor the 

 Thermometer can detect. - The Evaporation of Ice during 

 the severest Frost explained on that Supposition. Proba- 

 bility that the Metals would evaporate when exposed to the 

 Action of the Suns Rays were they not good Conductors of 

 Heat. Mercury is actually found to evaporate under the 

 mean Temperature of the Atmosphere. This Fact is a 

 striking Proof that FLUID MERCURY is a Non-conductor 

 of Heat. Probability that the Heat generated by the 

 Rays of Light is always the same in intensity ; and that 

 those Effects which have been attributed to Light ought 

 perhaps in all Cases to be ascribed to the Action of the 

 Heat generated by them. A striking Proof that the most 

 intense Heat does sometimes exist where we should not 

 expect to find it. Gold actually melted by the Heat which 

 exists in the Air of the Atmosphere^ where there is no 

 Appearance of Fire y or of anything red-hot. We ought 

 to be cautious in attributing to the Action of unknown 

 Powers, Effects similar to those produced by the Agency of 

 Heat. The most intense Heat may exist without leaving 

 any visible Traces of its Existence behind it. This im- 

 portant Fact illustrated by the necessary Result of an 

 imaginary Experiment. 



HOW far the possibility of the communication of 

 Heat between the integrant particles of a Fluid 

 may or may not be owing to the extreme mobility of 

 those particles, and to the infinitely short time that two 

 of them, of different specific gravities (owing to a dif- 



