4^2 Dr. CRAWFORD on the Power that 
the degree of expanfion as proportional to the increafe of hear, 
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 diftinctly traced, we are indebted for all the lucceeding im- 
provements in the philofophy of heat. By means of it men 
were enabled to eftablifh a variety of interefting fads, and to 
bring fome of the moll obfcure and intricate phenomena of 
nature to the teft of experiment. The opinion, that the heats 
inherent in various heterogeneous fubftances differed from each 
other in kmd, as well as in degree, was now exploded, fince all 
were found to produce fimilar effefts upon the thermometer. 
_ ® mcreafe and diminution of temperature in the different 
ieafons and climates, the laws which nature obferves in the 
heating and cooling of bodies, the melting, the vaporific, and 
mining 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 fubjeft, many curious queftions arofe, which have long 
exercifed the ingenuity of philofophers. That property of 
neat by which it is capable of expanding the denfeft and hardeft 
odies; its p 0Wer in producing fluidity; its tendency to an 
equilibrium ; and the caufes of its various diftribution through- 
out the different fubftances in- nature, have become the objefts 
of philosophical 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 con- 
tu ° ie a * r ’ kindle into flame, and continue to emit light 
eat, apparently from a fource within themfelves, till they 
axe con umed. Hence arofe the queftions concerning the pabu- 
