ftihfiJTing in tie Atmofphere-. I45 



heats of the vapours of water boiling are as the fenfible lieats 

 reciprocally, it being known, that the fpecific heat of the va- 

 pour of water heated to 180 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 fliown in the above table and 

 the notes) mav alfo be difcovered. 



Thus the fenfible heat of the vapour of boiling water baro- 

 meter 30 being 180'' above the freezing point (2ia« — 32" = 

 180'^) 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 

 barometer (lands at 38 inches, is 958 for — J/6'^6. 180 : : 

 940958 *. ... 



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

 I have alreadv ftated the grounds) exift in the atmofphere 

 when its denfi'ty is higher than 25, as it is in mofl of the in- 

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

 air, an inquiry into its latent heat at ditferent temperatures 

 below ebullition were fuperflnous. ^ But as it does exift in air 

 whofe denfity is 25 or lefs, fince it is found in air whofe den- 

 lity is 12-5, It becomes ncceflary to examine its latent heat in 

 fuch cafes, in all temperatures inferior to that pf ebullition. 

 Now, by analogy, I apprehend this latent heat in all inferior 

 temperatures may thus be determined. 



As ih? fen/ible heat of ebullition, when the barometer is 

 at 25 or below 25, is to the latent heat of the vapour at ebul- 

 lition, fo is \.\\cfaijihle heat of water heated to any inferior 

 degree above 32' to the latent heat of its vapour, rnuUiplied 

 by 5-222. Thus the fenfible heat of water in ebullition baro- 

 meter 25 being 171-4" (= 203-4"'-32°) its fpecific heat is 



g.S? (= L2l£_) the latent heat of the vapour of water at 



^ '7''4 ' 

 22" above congelation (that is 52" on Fahr. fcale) is 657 

 for -H- I7i"4' 987 :: 22^ l;6 X 5*22 = 657. The latent 

 heat of vapour in fuch cafes cannot be detcr.nined by experi- 

 ment, on account of the admixture of atmofphcric air: we 

 uuid therefore rcfort to analogv, which in this cafe is perfeA. 

 The latent heat of pure vapour at greater heights is more 

 confiderablc: thus at heights, at which the baromeler ftimds 

 at 20 inches, the latent beat of vapour whofe temperature is 

 22" above 32", as in the hft cafe, is 730; for the heat of 

 ebullition is 194-8% per table, rz 163-8% above 32 : and 

 the latent heat of the vapour at ebullition is i039. Ndw -H- 

 163-8. J 039 : : 32. 140 and 140 X 5-33 •= 730. 



• Hcnc- /()()i?6, bciiiK I'lo proJuft of i!o°x<)4.o, i» the lommon di- 

 TidcnH of iill Icnhhic litac bih'.i> l>:o°, when tr t Littat licat Qt llit vajjour 



Vol. XIV. No. 54- ^ ^^ 



