246 Mr. Cavendish’s Account of fame 
contraction by great degrees of cold, I fent a thermometer 
filled with oil of falfafras, and two others with fpirits of wine. 
One of thefe laft was filled with the higheft redtified fpirits I 
could procure, its fpecific gravity at 6o° of heat being ,8185 ; 
the other was intended to be filled with common fpirits, though 
from circumftances I am inclined to fufpedt that alfo to have 
been filled with the beft fpirits. Befides thefe, there was fent a 
mercurial thermometer, accurately adjufted, according to the 
directions of the Committee of the Royal Society, printed in 
the LXVlIth volume of the Tranfadtions ; and alfo the two 
fpirit thermometers ufed by Mr, Hutchins, which were filled 
with fpirits whofe fpecific gravity was ,8247. 
5. Thefe thermometers were compared together by expofing 
them to the cold, with their balls immerfed in a glafs veflel 
filled with diluted oil of vitriol. They were at times alfo com- 
pared in cold more violent than the natural cold of the climate, 
by adding fnow to the acid in which they were tried, in which 
cafe care was taken to keep the mixture frequently ftirred. Oil 
of vitriol was recommended for this purpofe, as a fluid which 
would moft likely bear any degree of cold without freezing, 
and whofe natural cold might be much iticreafed by the addition 
of fnow. It feems to have anfwered the purpofe very well, 
and not to have been attended with any inconvenience. 
During the firft comparifon of thefe thermometers, a whitifh 
globule, fuch as thofe which appear in frozen oil, was ob- 
ferved in the tube of the thermometer filled with oil of faffa* 
fras. This appearance of congelation did not much increafe ; 
but two days after a large air bubble was found in its ball, 
which prevented Mr. M c Nab from making farther obferva* 
lions with it. 
It 
