Ill 
and the Mode of its Communication. 
calorific rays, I could no longer entertain any doubts respecting 
the agency of radiation , in the heating and cooling of bodies. 
Many important points however still remained to be investigated, 
before distinct and satisfactory ideas could be formed, respecting 
the nature of those rays, and the mode of their action. 
I had hitherto made use of but one metal (brass) in my ex- 
periments ; and that was not a simple, but a compound metal. 
The first subject of enquiry which presented itself, in the pro- 
secution of these researches, was to find out whether or not 
similar experiments made with other metals would give similar 
results. 
Exper. No. 14,. Procuring from a gold-beater a quantity of 
leaf gold and leaf silver, about three times as thick as that 
which is commonly used by gilders, I covered the surfaces of 
the two large cylindrical vessels, No. 1 and No. 2, with a single 
coating of oil varnish; and, when it was sufficiently dry for my 
purpose, I gilt the instrument No. 1 with the gold leaf, and co- 
vered the other, No. 2, with silver leaf. When the varnish was 
perfectly dry and hard, I wiped the instruments with cotton, 
to remove the superfluous particles of the gold and silver, and 
then repeated the experiment so often mentioned, of filling the 
instruments with boiling hot water, and exposing them to cool, 
in the air of a large quiet room. 
The time of cooling through the given interval of 10 degrees, 
was just the same as it was before, when the natural surface of 
these brass vessels was exposed naked to the air. I repeated 
the experiment several times, but could not find that the difference 
in the metals made any difference in the times of cooling. 
Exper. No. 15. Not satisfied to rest the determination of so 
important a point on a trial with three metals only, brass, gold, 
