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 meUed by the Heat which 

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

 Appearance of Fire, 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- 



