270 ON HEAT. 



Experiments have demonstrafecl that the other must be a gas with which we 



and oberva- ^re still unacquainted, in a separate state. Jt must be speci- 

 tions on thein- ^ „ ,. , , ,, i , t , i . , 



flammable gas ncally lighter than carbureted hydrogen; must contain less car- 



trom peat. bon and more hydrogen. Were we to suppose it a species of 

 carbureted hydrogen, it would not be difficult to deduce its 

 specific gravity and its constituents, from the preceding expe- 

 riments. But if oxygen enters into its composition, as is 

 by no means improbable, the preceding experiments do not 

 furnish us with the requisite data. At any rate, it would be 

 premature, at present, to enter upon any such investigation till 

 a greater number of the inflammable gases yielded by vege- 

 tables be examined. 



II. 



Observations on Professor Leslie's Theory of Caloric. In a Let- 

 ter from Z)r . H A L L I D A y , of Ha lesworth. 



To Mr. NICHOLSON. 



S I R, 



Whether raai- ^^py£g^ reading Professor Leslie's very excellent treatise 

 ant caloric be ^ r ■,? ^ • ■ ■ r^^ 



propagated on heat, I confess 1 became a convert to his ingenious Theory 



with great ve- of Radiant Caloric, and then instituted a few experiments, not 

 much different from his, with the view of confirming my opi- 

 nions still more. These experiments, however, which I fear 

 were not performed with too tnuch accuracy, have somewhat 

 shaken my faith in the Professor's theory; and I am now 

 more than ever convinced of the truth of the generally- received 

 notion, viz. " that caloric is capable of being projected in 

 right lines with great velocity, and that these lines obey nearly 

 the same laws of motion as the rays of light." I shall not 

 enter into a detail of the experiments at present, but merely 

 state their results, and the reasons why I have been induced to 

 alter my sentiments; and I shall only advert to those from 

 which Mr. Leslie has inferred the theory he has formed of 

 radiant caloric. 



Mr. 



