[ 33» ] 



the above circumftances, cools it one degree. If the faturability 

 of the air were greater, it would undoubtedly cool it more, and in a 

 fhorter time. 



Lei DEN frost's experiments on evaporation in very high degrees 

 of heat, fince -verified and extended by Ziegler, SaulTure, Spalanzani, 

 a*id D'Antic, and'Commented on by Lambert, are excealing curious; 

 but as they have no relation to meteorology, (and though I have 

 myfelf repeated them), I fhall not introduce them in this effay, but 

 pafs to the fecond objed of enquiry relative to the moiflure of 

 the atmofphere, namely the flate of -vapour when contained in it. 



CHAP. 



H. 



Of the State of Vapour fubjijling in the Atmofphere. 



Vapour or Moifture in the atmofphere may fubfiflin denfeair, 

 or in air highly rarefied : that it is found in the former is well known, 

 and that it may fubfift in the latter appears by the obfervalions 

 of Bouguer, for he faw clouds three or four hundred toifes above 

 Chiromboracho, and confequently at the height of twenty- two 

 thoufand five hundred and twenty-eight Englifh feet, or 4,3 miles 

 iOver the level of the fea ; a height at which in the temperature 



of 



•• 1 

 4- 



