for adjufting thermometers. 835 
In making experiments with thermometers, it evi- 
dently is equally neceffary that the quickfilver in the 
tube fliould be of the fame heat as that in the ball, as it 
is in adjufting the boiling point: for this reafon, in trying 
the heat of liquors much hotter or colder than the air, 
the thermometer ought, if poffible, to be immerfed as 
far as to the top of the column of quickfilver in the tube. 
As this, however, would often be very difficult to exe- 
cute, the obferver will frequently be obliged to content 
himfelf with immerfing it to a much lefs depth. But 
then as the quickfilver, in a great part of the tube, will 
be of a different heat from that in the ball, it will be ne- 
ceffary, where any degree of accuracy is required, to 
make a correction, on that account, to the heat fliewn by 
the thermometer. If the heat of the quickfilver in the 
tube be known, the correction may readily be made by 
help of the annexed table ; the only difficulty lies in efti- 
mating what that heat may be. In all probability the 
heat of the quickfilver in the tube will not be very dif- 
ferent from that of the air which furrounds but as 
that 
(h) This mull evidently be the cafe, unlefs the quickfilver in the tube is 
confiderably heated by its conta£l with that in the ball. To fee whether this 
was the cafe, fome fand was heated in a fmall copper difh over a lamp to the 
heat of about 212 0 , and the abovementioned tube, without a. ball, laid hori- 
zontal with the end extending about half an inch over the fand; but, to prevent 
its being heated thereby, a piece of wood, about a quarter of an inch thick, 
5 M 2 was 
