[ 334 ] 



Hence fince, according to Mr. Watt, the fenfible heats of the 

 vapours of boiling water at different barometrical heights are as the 

 barometrical heights reciprocally, and the fpecific heats of the vapours 

 of w^ater boiling are as the fenfible heats reciprocally, it being 

 known, that the fpecific heat of the vapour of water heated to i8o 

 degrees above the freezing point is 940. The fpecific or latent heat 

 of the vapour of boiling water, whofe fenfible heat is known, (and 

 it may be known by the barometrical height as fhewn in the 

 above table and the notes) may alfo be difcovered. 



Thus the fenfible heat of the vapour of boiling water barometer 

 30 being 180° above the freezing point (212° — 32!'=i8oP) and 

 the fpecific or latent heat of vapour, whofe fenfible heat is 

 2o8'',56 (that is 176,56 above 32'') as it is when the barome- 

 ter ftands at 28 inches, is 958 for ^ 176,56. 180 :: 940.958*. 



As pure invifible vapour does not in my opinion (of which 

 1 have already flated the grounds) exift in the atmofphere when 

 its denfity is higher than 25, as it is in moft of the inhabited 

 parts of the globe, but is always in this cafe united to air, an 

 enquiry into its latent heat at different temperatures below ebul- 

 lition were fuperfluous. But as it does exift in air whofe denfity is 

 25 or lefs, fince it is found in air whofe denfity is 12,5, it becomes 

 necefiTary to examine its latent heat in fuch cafes, in all tempera- 

 tures 



* Hence 169206, being the product of l8o°X94o, is the common dividend of all 

 fenfible heats ielow iSo". when the latent heat of the vapour is fought at barometrical 

 heights below 30 inches. 



