for adjujling thermometers. 837 
racy, he may find the heat of the furrounding air by 
holding the ball of a fmall thermometer near the tube 
of 
the degree of heat of the fluid, and’ the quantity of fleam which it furnifhes* 
and according to the nature of the fire by which it is heated; yet as the 
experiments may perhaps ferve in fome meafure to redlify our ideas on this head* 
we will give the refult. When the abovementioned tube without a ball *, the 
length of the column of quickfilver in which was 15 inches, was held perpen- 
dicularly over the veflel of boiling water, with its bottom even with the fur face 
of the water, the heat of the quickfilver was in all the trials we made from 68' 
to 28° hotter than the air of the room. If the tube was held inclined to the 
horizon, in an angle of about 30°, with the bottom of the column of quick- 
filver reaching not more than three quarters of an inch within the circumference 
of the pot, fo that the column of quickfilver was as little heated by the fleam as- 
could eafily be done, it was from 30 to 7 0 hotter than the air. When a fhorter. 
tube of the fame kind, in which the column of quickfilver was feven inches,,, 
was ufed, the quickfilver was from 62 to 44 0 hotter than the air, when held-, 
perpendicularly, and from 49 to 36° hotter when held inclined. The water in. 
thefe trials frequently boiled pretty fafi, but never very violently. It was im 
general heated over a portable black lead furnace placed in the middle of the room ; 
but it was once heated over an ordinary chafing- difli, when the quickfilver in- 
the long tube, held perpendicularly, was found to be 64° hotter than the air* 
When the experiments were tried without doors, the heat of the quickfilver in* 
the tube would vary very much, according as the wind blew the fleam and hot; 
air from or towards the tube, but it fometimes rofe as high as it did within, 
doors. 
The moft convenient method we know of making thefe tubes without a ball is, 
to fill a thermometer in the ufual manner,. and heat the ball till there is a proper 
quantity of quickfilver in the tube, and then. to make the column of quickfilver 
feparate.at the neck of the ball,., and run to the extremity of the tube, fo as to 
leave a vacuum between the ball and the column of quickfilver, as is expreffed 
in fig. 2. where the (haded part ad reprefents the column of quickfilver, and 
ba that part in which there is a vacuum. The tube muff then be fealed fome.- 
See p. 830. h 1, 
where 
