COUNT RUMFORD. 161 



caution. His conclusion from his experiments was that, 

 if heat be a substance a fluid sui generis it must be 

 something so infinitely rare, even in its condensed state, 

 as to baffle all our attempts to discover its gravity. 

 But " if the opinion which has been adopted by many of 

 our ablest philosophers, that heat is an intestine vibra- 

 tory motion of the constituent parts of bodies, should 

 be well founded, it is clear that the weights of bodies 

 can be in no wise affected by such motion." The weight 

 of a bell, he urges in another place, is not affected by 

 its sonorous vibration. 



Early in the year 1803, he being then in Munich, 

 Eumford broke ground in the domain of radiant heat. 

 He prepared bright metallic vessels, filled them with 

 hot water, placed them in a large and quiet room, and 

 observed the time required to cool them down a certain 

 number of degrees. Covering some of his vessels with 

 Irish linen and leaving others bare, he found, to his 

 surprise, that the covered vessels were more rapidly 

 chilled than the naked ones. Comparing in the same 

 room a thick glass bottle, filled with hot water, with a 

 tin bottle of the same shape and size, he found that the 

 water in the glass vessel cooled twice as rapidly as that 

 in the tin one. \Vhen, moreover, he coated his metallic 

 vessel with glue, the cooling process was hastened, as it 

 had been by the linen. Applying a second, a third, and 

 a fourth coating of glue, he found the chilling pro- 

 moted. Here, however, he came to a point where the 

 addition of any further coatings produced a retardation 

 of the chilling. Painting some of his vessels black and 

 some white, he found the times of cooling to be practi- 

 cally the same for both a result which he seems to 

 have afterwards forgotten. From these and other ex- 

 periments of the same kind he drew the just conclusion 



