345 Profe efor WiLLIAa ms s Account of cm. 
air heavy, and the winds {mall and variable for feveral days ; the 
vapours, inftead. of difperfing, muft have. been rifing-and con: 
ftantly collecting i in the air, until the atmofphere became highly: 
charged with. an uncommon quantity of them.. 
.A large quantity. of the. vapours, thus colleded.in the at» 
mofphere,. on the 19th of May, were floating near the furface: 
of the earth. Wherefoever, the fpecific gravity of any vapour: 
is lefs than the fpecific gravity of theair, by the.laws.of fluids;. 
füch a vapour. yi cain in the air. Where. Bde fonika : 
of the vapour and aira are Eq foi. cR vapour, will, ien ir 1 
reft,-—floating or fwimming in the atmofphere, without afcend..- 
ing or defcending.. From. the barometrical ob(ervations itp... 
pears,.. that. the, weight or. gravity, of the atmofphere was gradu 
ally growing lefs, from the morning of the 19th of May; until 
the. evening. And, hence. the vapours, in:moft places; were 
dening from, the, hi er parts.of the-atmofphere, towards 
a fs of, the cath... From the obfervation made at: Pepa. 
r ‘appears, that in fome places the vapours were afcend> ` 
ing, si they, arofe to an height in: which the air was-of the > 
x rag gni; whey, kp emn v and ec 
clude;, xig PR where the ire — heed; or bea 
came of the. fame, fpecifie: gravity- as: the: air,, muft:have beent 
| nd RE dicato: Amiens wag = 
ay pm feng i in the atmof= = 
