Experiments upon Heat . 275 
to the end of a common barometer tube about 32 Inches in 
length, and by means of this opening the fpace between the 
internal furface of the glafs ball and the bulb of the thermo- 
meter was filled with hot mercury, which had been previoufly 
freed of air and moifture by boiling. The ball, and alfo the 
barometrical tube attached to it, being filled with mercury, the 
tube was carefully inverted, and its open end placed in a bowL 
in which there was a quantity of mercury. The inftrument 
now became a barometer, and the mercury defcending from 
the ball (which was now uppermoft) left the fpace fur- 
rounding the bulb of the thermometer free of air. The mer- 
cury having totally quitted the glafs ball, and having funk in 
the tube to the height of 28 inches (being the height of the 
mercury in the common barometer at that time), with a lamp 
and a blow-pipe I melted the tube together, or fealed it her- 
metically, about three-quarters of an inch below the ball, and 
cutting it at this place with a fine file, I feparated the ball 
from the long barometrical tube. The thermometer being 
afterwards filled with mercury in the common way, I now 
pofleffed a thermometer whofe bulb was confined in the center 
of a T orricellian vacuum , and which ferved at the fame time as 
the body to be heated, and as the inftrument for meafuring the 
heat communicated. 
Experiment N° r. 
With this inftrument (fee fig. 1 .Tab.VI.) I made the following 
experiment. Having plunged it into a veflel filled with water, 
warm to the 1 8th degree of Reaumur’s fcale, and fuffered it to 
remain there till it had acquired the temperature of the water, that is 
O o 2 to 
