3*2 Dr. Fordyce’s Account of 
\ 
equally heated according to its capacity ; whether equal vi- 
brations excited fhall always produce the fame quantity of 
heat ; whether a chemical attra&ion taking place between an 
equal quantity of two fubflances fhall always produce an equal 
quantity of heat ? 
The importance of this enquiry is fufficiently evident, fince 
if the fame quantity of fuel being burnt the fame quantity of 
heat be always produced, our whole attention will be to take 
care that no part of the heat fhall be lofl ; but if burning the 
fuel under one fet of circumftances will adiually produce a 
greater quantity of heat than burning it in other circumftances; 
or if burning it, will produce a great heat in one place, which 
cannot be carried to another place, but will be again anni- 
hilated, a very different attention muff be paid. I was fir ft led 
into this train of thinking by obferving reverberatory furnaces* 
Formerly I had no doubt but that it was obvious, that the fame 
quantity of fuel burnt would produce the fame quantity of heat.; 
but having occafion to try fome experiments in reverberatory- 
furnaces, where great heat and cleannefs were required, I 
tried to heat the furna'ce with charcoal and coak, or pit-coal 
charred, that is, burnt till no fmoak arifes, but could never 
produce the heat required,, although I could do it eafily with 
coal. I infulated my furnace, fo that after twenty- four hours 
ftrongeft fire, it did not feel in the leaf! warm on the outfide. I 
heightened the chimney ; but all to no effect : in the fire-place 
the heat was fufficient to melt malleable iron, but in the labo- 
ratory, in the horizontal part of the chimney, the heat was 
trifling. Since that time I have made various experiments to 
afeertain the propofition laid down. The following one, which 
has been varied and repeated with the fame refult, may, per- 
haps,, draw the attention of chemifts to this point. 
5 
I formed 
