4 1 2 Of the Propagation of Heat 



coincided with the center of the globe in which it was 

 shut up. The end of the cylinder above the upper 

 choak being now heated and drawn out to a point, or 

 rather being formed into the figure of the frustum of a 

 hollow cone, the end of it was soldered to the end of a 

 barometrical tube, by the Ijelp of which the cavity of 

 the cylinder and globe containing the thermometer was 

 completely voided of air with mercury ; when, the end 

 of the cylinder being hermetically sealed, the barometri- 

 cal tube was detached from it with a file, and the ther- 

 mometer was left completely shut up in a Torricellian 

 vacuum, the centre of the bulb of the thermometer be- 

 ing confined in the centre of the glass globe, without 

 touching it in any part, by means of the two choaks in 

 the cylinder, and the button upon the end of the tube. 

 (See Fig. 2.) 



Of these instruments I provided myself with two, as 

 nearly as possible of the same dimensions ; the one, 

 which I shall call No. i, being voided of air, in the 

 manner above described ; the other, No. 2, being filled 

 with air, and hermetically sealed. 



With these two instruments (see Fig. 2) I made the 

 following experiments upon the nth of July last at 

 Manheim, between the hours of ten and twelve, the 

 weather being very fine and clear, the mercury in the 

 barometer standing at 27 inches n lines, Reaumur's 

 thermometer at 15, and the quill hygrometer of the 

 Academy of Manheim at 47. 



Experiments No. 3, 4, 5, and 6. 



Putting both the instruments into a mixture of 

 pounded ice and water, I let them remain there till the 

 mercury in the inclosed thermometers rested at the 



