VOL. LXXVI.] PHILOSOPHICAL TRANSACTIONS. 100 



bulb, the bulb of the thermometer remained fixed in the centre of the ball, and 

 consequently was cut off' from all communication with the external air. In the 

 bottom of the glass ball was fixed a small hollow tube or point, which projecting 

 outwards was soldered to the end of a common barometer tube about 3*2 inches 

 in length, and by means of this opening the space between the internal surface 

 of the glass ball and the bulb of the thermometer was filled with hot mercury, ' 

 which had been previously freed of air and moisture by boiling. The ball, and 

 also 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 instrument now became a barometer, and the mer- 

 cury descending from the ball, which was now uppermost, left the space sur- 

 rounding the bulb of the thermometer free of air. The mercury having totally 

 quitted the glass ball, and having sunk 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 lube together, or sealed it hermetically, about 

 -I- of an inch below the ball, and cutting it at this place with a fine file, I sepa- 

 rated the ball from the long barometrical tube. The thermometer being after- 

 wards filled with mercury in the common way, I now possessed a thermometer 

 whose bulb was confined in the centre of a Torricellian vacuum, and which 

 served at the same time as the body to be heated, and as the instrument for 

 measuring the heat communicated. 



Exper. 1. — Having plunged this instrument into a vessel filled with water, 

 warm to the 18th degree of Reaumur's scale, and suffered it to remain there till 

 it had acquired the temperature of the water, that is, till the mercury in the in- 

 closed thermometer stood at 1 8", I took it out of this vessel and plunged it sud- 

 denly into a vessel of boiling water^ and holding it in the water (which was kept 

 constantly boiling) by the end of the tube, in such a manner that the glass ball, 

 in the centre of which was the bulb of the thermometer, was just submerged, 

 I observed the number of degrees to which the mercury in the thermometer had 

 arisen at different periods of time, counted from the moment of its immersion. 

 Thus, after it had remained in the boiling water 1 min. 30 sec. the mercury had 

 risen from 18° to 27°; after 4 minutes had elapsed, it had risen to 44°^; and 

 at the end of 5 minutes it had risen to AS°-^. 



Exper. 2. — Taking it now out of the boiling water I suffered it to cool 

 gradually in the air, and after it had acquired the temperature of the atmos- 

 phere, which was that of 15°e. the weather being perfectly fine, I broke off a 

 little piece from the point of the small tube which remained at the bottom of the 

 glass ball, where it had been hermetically sealed, and of course the atmospheric 

 air rushed immediately into the ball. The ball surrounding the bulb of the 

 thermometer being now filled with air, I re-sealed the end of the small tube at 



