526 On Heal €? Cold produced by Mechanical, ec. 
‘The experiments and observations hitherto 
related go principally to ascertain facts with- 
out any reference to the theory of them: This 
however may be given in a few words, and 1g 
the same that is ascribed to Mr. Lambert by 
Messrs. Saussure and Pictet and by them adopt- 
ed. He conceives that a vacuum has its proper 
capacity for heat, the.same as air, or any other 
substance; and that the capacity of a vacuum 
for heat is Jess than that of an equal volume 
of atmospherical air; also that the denser air is, 
the Jess is its capacity for heat: upon: these 
principles the phenomena are easily referable 
to that class of chemical facts where heat and 
cold are generated by the mixture of two dif 
ferent bodies.—If this theory be right, and I 
think there is little doubt of it, we may hence 
be led into a train of experiments, by which the 
‘absolute capacity of a vacuum for heat may be — 
determined; and likewise the capacities of the 
different gases for heat, by a method wholly 
new :—but this must be left to future inves- 
tigation. 
