the Royal Society’s Injiruments . 379 
the ball, is much greater; as fpirits of wine expand much 
more by heat than quickfilver : for which reafon fpirit 
thermometers are not fo proper for trying the heat of 
liquors as thofe of quickfilver. 
Another circumftance which ought to be attended to 
in adjufting the boiling point of a thermometer is, that 
the ball fhould not be immerfed deep in the water; for, 
if it is, the fluid which furrounds it will be compreffed 
by confiderably more than the weight of the atmofphere, 
and will therefore acquire a fenfibly greater heat than it 
would otherwiie do. The moft convenient veflel I 
know for adjufting the boiling point is reprefented in 
fig. 1. abcd is the veflel; ab the cover, made to take on 
and off readily; e a chimney to carry off the fteam; fg 
the thermometer, paffed through a hole mm in the cover, 
and refting in a little bag fattened to the wire hk, in- 
tended to prevent the ball from being broken by acci- 
dentally falling to the bottom. This wire is made fo as 
to be raifed higher or lower at pleafure, and muft be 
placed at fuch a height that the boiling point fhall rife 
very little above the cover. The hole mm is flopped 
with bits of cork or tow. By this means, as the tube is 
inclofed in a veflel intirely filled with the fteam of boil- 
ing water, the quickfilver in it is heated to the fame de- 
gree as that in the ball ; and befides, that part of the tube, 
on which the boiling point is to be placed, is defended 
from the vapour, fo that it is eafy making a mark on the 
glafs with ink. If fuch a veflel as this is ufed, the 
thermometer will be found to ftand not fenfibly higher 
Vol. LX VI. E e e when 
