1 
Dr. Bell on the Generation of 
ing cold by fome occult operation. The expe¬ 
riments feem to have been made with fufHcient 
accuracy ; but the conclufion drawn from them 
is liable to ftrong objedlion. For, in forming it, 
feveral circumftances have been overlooked, 
which, in my opinion, afford an eafy explanation 
of all the phenomena, on principles already 
known, without referring them to a new law of 
the animal body, which probably does not exift. 
Thefe circumftances I fhall endeavour to point 
out. 
I. The firfl caufe which prevented their bodies 
from receiving a greater increafe of heat was, 
‘The rarefaction of the air with which they were fur- 
rounded. 
The quantity of heat which different fubftances 
contain, is, in general, in proportion to their 
denfity ; and, in this proportion, they communi¬ 
cate more or lefs of it to others. A cubical foot 
of water, contains a much greater quantity of 
heat, than a cubical foot of air, of the fame 
temperature: and, if a third fubftance be added, 
its temperature will be confiderably changed by 
the hot water, while by the hot air it will hardly 
be changed in any perceptible degree. Many 
fa£h may be adduced, which fcrve to illuftrate, 
and, at the fame time, are explained by this 
caufe. Thus, the fleam of boiling water will 
fcald a perlon’s hand, which can fupport the heat 
of air, of the fame temperature. And thus per¬ 
haps 
