Experiments upon Heat. 53 
over the divisions of the thermometer, marking 70° and every 
tenth degree from it, descending, to io° of the scale. I con- 
tinued the cooling to o°, or the temperature of the ice and 
water, in very few instances, as this took up much time, and 
was attended with no particular advantage, the determination 
of the times taken up in cooling 60 degrees of Reaumur's 
scale, that is to say, from 70 0 to io°, being quite sufficient to 
ascertain the conducting power of any body whatever. 
During the time of cooling in ice and water, the ther- 
mometer was constantly moved about in this mixture from 
one place to another ; and there was always so much pounded 
ice mixed with the w’ater, that the ice appeared above the 
surface of the water ; the vessel, which was a large earthen 
jar, being first quite filled with pounded ice, and the water 
being afterwards poured upon it; and fresh quantities of 
pounded ice being added as the occasion required. 
Having described the apparatus made use of in these expe- 
riments, and the manner of performing the different ope- 
rations, I shall now proceed to give an account of the expe- 
riments themselves. 
My first attempt was to discover the relative conducting 
powers of such substances as are commonly made use of for 
clothing; accordingly, having procured a quantity of raw 
silk, as spun by the worm, sheep’s wool, cotton wool, linen in 
the form of the finest lint, being the scrapings of very fine 
Irish linen, the finest part of the fur of the heaver, separated 
from the skin, and from the long hair, the finest part of the 
fur of a white Russian hare, and Eider down ; I introduced suc- 
cessively 16 grains in weight of each of these substances into 
the globe of the passage-thermometer, and placing it carefully 
