4$T Dr. crawford on the Power that 
the degree of expanfion as proportional to the increafe of heat,, 
philofophers have endeavoured by means of the former to ren- 
der the latter obvious to the fenfes. 
To this important invention, the author of which cannot 
be diftindtly traced, we are indebted for all the iucceeding im- 
provements in the philofophy of heat. By means of it men. 
were enabled to edablifh a variety of interefling facls, and to 
bring fome of the mod: obfcure and intricate phenomena of 
nature to the ted: of experiment. The opinion, that the heats 
inherent in various heterogeneous fubdances differed from each- 
other in kind, as well as in degree, was now exploded, fince all 
were found to produce dmilar effects upon the thermometer 
The increafe and diminution of temperature in the different 
feafons and climates, the laws which nature obferves in the 
heating and cooling of bodies, the melting, the vaporific, and 
fhining points, and the degrees of heat in the animal, the 
mineral, and the vegetable kingdoms, were accurately deter- 
mined. In confequence of the attention that was paid to* 
this fubjed, many curious quedions arofe, w'hich have long 
exercifed the ingenuity of philofophers. That property of 
heat by which it is capable of expanding the denfed and harded 
bodies ; its power in producing fluidity ; its tendency to an 
equilibrium ; and the caufes of its various didribution through- 
out the different fubdances in nature, have become the objects 
of philofophical enquiry. It was obferved, that fome bodies 
on expofure to heat, become red and luminous, but are inca- 
pable of producing flame, or of maintaining fire : that, on 
the contrary, others, by the application of fire, and the eon- 
tad of frefh air, kindle into, flame, and continue to emit light 
and heat, apparently from a fource within themfelves, till they 
are confiunied* Hence arofe the quedions concerning the pabu- 
lum 
