Dr, Fordyce’s Account, &c. jii 
Dr. Cullen, that cold was alfo produced by converting bodies 
into vapour. It has been fince that time found, that the oppo- 
se condenlations, viz, of vapours into fluids, or fluids into l'olids, 
generate heat. Cramer was the firft who took notice of the 
different conducting powers of different bodies, in his “ Ars 
“ Docimaftica,” P. I. § 274. Scholium. 
The power of animal bodies, of refifting the cold of the 
medium they are in, has been long known. Mr. Ellis took 
notice of their being alfo able to refift the heat. Dr. Cullen 
afcribed this power to a peculiar quality in animals different 
% 
from the powers of inanimate matter. You, Sir, faw a con- 
firmation of this power being very great when we kept a dog 
of no large fize (he might weigh, as far as I can recolleCt, about 
twenty-five pounds, not more) in air heated to 160 degrees 
of Fahrenheit’s thermometer for half an hour. We took 
him out with only the addition of a few degrees of heat; not 
from any unealinefs of the animal, but from being fatisfied 
with the experiment. This power has been fhewn by Mr. 
Hunter to extend to vegetables. The degree of heat one body 
is capable of impregnating another with, was hardly touched 
upon by any author before Dr. Crawford, who has done a 
great deal in this branch, and is ftill purfuing it. 
The fubjeCl of the prefent enquiry is different from all thefe. 
The propofition is, fuppofing we can make an application to a 
cold body, fo as to produce heat in it, and this application be made 
with the fame force to the fame body, whether by this means an 
equal quantity of heat will always be produced in an equal 
quantity of matter ? That is, for inftance, whether an equal 
quantity of the rays of the fun being thrown on an equal lur- 
face of the fame matter, fo that they fhall be equally loft, 
bent, or refle&ed, an equal mafs of matter below fhall be 
Vol. LXXVII. Z 2 equally 
