Life of Count Rumford. 459 



questionable it may appear, till it has been proved by 

 direct and decisive experiment." Thus, he had taken 

 for granted, as apparently everybody had done, " that 

 heat had a free passage in all directions, through all 

 kinds of bodies." But this assumption alike of the 

 learned and the unlearned, and which, to his knowledge, 

 had never been called in question, is erroneous. To 

 this mistaken belief he attributes " the little progress 

 that has been made in the investigation of the science 

 of heat, a science assuredly of the utmost importance 

 to mankind." He began his own experiments on the 

 subject under that delusion, and only an accidental dis- 

 covery convinced him of his error, and led him to 

 recognize first that air is a non-conductor of heat; and 

 even then he had been so blinded by his prepossession 

 as not at once to recognize the most evident proof that 

 liquids also would not admit of the free passage of heat 

 in all directions through them. Having in a previous 

 Essay announced his discovery that steam and flame are 

 non-conductors of heat, he proceeds to describe the ex- 

 periments which proved to him that " although the 

 particles of any fluid individually can receive heat from 

 other bodies or communicate it to them, yet among 

 these particles themselves all interchange and communica- 

 tion of heat is absolutely impossible." 



The Count had often burned his own mouth, and seen 

 other persons burn theirs, while eating at dinner of a dish 

 much used in England, namely, apple-pies, or apples 

 and almonds mixed. Apples thus cooked retained their 

 heat for a surprising length of time. Why was it so ? 

 There was also a great difference in this respect between 

 several other cooked foods. The philosopher tried to 

 account to himself for the fact which had engaged his 



