210 STATE OF VAPOUR SUBSISTING Itf THE ATMOSPHERE. 



fible heat is 2Q8°,56 (that is 176,56 above 32°) as it is when 

 the barometer ftands at 28 inches, is 958 for -£f 176,56. 180 

 : : 940.958 *. 

 Untombined As pure invifible vapour does not in ray opinion (of which I 



vapour confiaer- nave already ftated the grounds) exift in the atmofphere when 

 its denfity is higher than 25, as it is in me# 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 neceflary to examine its latent heat in fuch cafes, in 

 all temperatures inferior to that of ebullition. Now, by ana- 

 logy, I apprehend, this latent heat in all inferior temperatures 

 may thus be determined : 

 Determination of As the fetifible heat of ebullition, when the barometer is at 25 



the latent heat of or De i ow 25 is to the latent heat of the vapour at ebullition, fois 

 pure vapour. r . 



the ftnfible heat of water heated to any inferior degree above 



32° to the latent heat of its vapour, multiplied by 5,222. Thus 

 the fenfible heat of water in ebullition barometer 25 being 

 171°,4 (= 203°,4-32°) its fpecificheat is 987 / = 169206 j 



the latent heat of the vapour of water at 22° above congela- 

 tion (that is 52 on Fahr. fcale) is 657 for 4r 171°, 4. 987 : : 

 22°. 126 x 5,22 = 657. The latent heat of vapour in fuch 

 cafes cannot be determined by experiment on account of the 

 admixture of atmofpheric air, we mud therefore refort to ana- 

 logy, which in this cafe is perfect. 



The latent heat of pure vapour at greater heights is more 

 confiderable : thus at heights, at which the barometer ftands at 

 20 inches, the latent heat of vapour whofe temperature is 22* 

 above 32°, as in the laft cafe, is 730 ; for the heat of ebulli- 

 tion is 194°,8, per table, == 162°,8 above 32°; andthelatent 

 heat of the vapour at ebullition is 1039. Now —• 162,8. 

 1039 : : 2°. 140 and 140 x 5,22 =730. 



As air is cooled by the reception of moifture diflfolved in it, 

 we muft infer that its capacity for containing heat is increafed, 

 and hence moift air is more difficultly heated or cooled than dry 

 air of the fame temperature. (For the cold proceeds from the 

 abforption and not from theexpulfion of caloric.) 



• Hence 169206, being the produft of 180° X940, is the com- 

 mon dividend of all fenfible heats belowo 180° . when the latent heat 

 •f the vapour is fought at barometrical heights below 30 inches. 



4 The 





