no Count Rumford's Enquiry concerning the Nature of Heat , 
had been removed to more than 8 inches from the ball to which 
it was presented; the other vessel, which had not been blackened, 
remaining in its former situation, at the distance of 2 inches 
from its ball. 
The result of this experiment appeared to me to throw a new 
light on the subject which had so long engaged my attention ; 
and to present a wide and very interesting field for farther 
investigation. 
I could now account, in a manner somewhat more satisfactory, 
for those appearances in the foregoing experiments which were 
so difficult to explain, — for the acceleration of the passage of the 
heat out of my instruments, which resulted from covering them 
with linen, varnish, &c. and I immediately set about making 
a variety of new experiments, from which I conceived I should 
acquire a farther insight into those invisible mechanical opera- 
tions which take place when bodies are heated and cooled. 
Finding so great a difference in the quantities of calorific rays 
which are thrown off by the polished surface of a metal, when 
exposed naked to the cold air, and when blackened , I now pro- 
ceeded to make experiments, to ascertain whether or not all 
those substances with which the sides of my cylindrical vessels 
had been covered, and which had been found to expedite the 
cooling of those instruments, would also facilitate the emission 
of calorific rays from the surfaces of the instruments I presented 
to the balls of my thermoscope ; and I found this to be the case 
in fact. 
As the results of all these experiments proved, in. the most 
decisive manner, that all the substances which, when applied to 
the metallic surfaces of my large cylindrical vessels, had expe- 
dited their cooling, facilitated and expedited the emission of 
