refpetiing Heal or Caloric. 219 



is made, fhould be alfo determined-, that it may be known 

 how many ounces or pounds of metal have alfo been heated 

 to the fame degree. 



The converfe may be exhibited by the fame apparatus by 

 a different mode of operating. Detach the veffel A from the 

 veffel E; invert it, and fill it with water, previoufly deprived 

 of air bv boiling or b\ the air-pump, and, having (hut the 

 cock B, again invert it and join it to the veffel E. Fill the 

 latter with mercury in the mann'er that has been already de- 

 fcribed, and to the cock b adapt an iron tube, of 31 or 33 

 inches in length, to defccnd vertically into a bafon of mer- 

 cury. If the cocks B b be now opened, all the others being 

 fhut, mercury will defcend from E, through the tube fitted 

 to /;, into the bafon in which the lower extremity of the tube 

 is, and the water will pafs from A into E, leaving a vacuum 

 in A. When the water has all paffed out of A, fhut the 

 cock B. 



If one atmofphere be now introduced into E,- and, the 

 cocksy and b being fhut, be compreffed into a half, a fourth, 

 or a fifth of its original volume, by means of a proportionate 

 column of mercury in the tube FG, heat will be expreffed 

 from the air, which muft pafs off through the fides of the 

 veffel E. Allow the apparatus to ftand for fome hours, till 

 every thing connected with it has come to the common tem- 

 perature. Then open the cock B, and the compreffed air, 

 finding itfelf at liberty, will pafs up into the vacuum 

 in A, where it will find fpace to expand itfelf to its natural 

 volume, the quantity employed being one meafure, or, in 

 other words, equal exaftlv to the capacity of A. The 

 mercury fhould alfo be allowed, by opening the cock F, to 

 afcend till it reach the cock B. But the air, in refuming; 

 its original volume, will demand heat from the materials of 

 which A is conftructed, and from the thermometric fluid 

 of A, fafter than they can receive it from the atmofphere and 

 contiguous bodies, efpecially if defended by a covering made 

 of a bad conducting fubftance; and, as a neceffary con- 

 fcquer.ee of this, the thermometric fluid will fall in the 

 tube FG. 



If heat be thus detected paffing from or into air by mere 

 F f 2, preffure_, 



