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very next SeB. he afcribes it to Rarcfadion, when he 
fays, ^‘That when a Wind blowing obliquely upwards 
« caufes a Cloud to rife into a thinner Air (/. e, fpe- 
« cifically lighter than it felf ) the 'Fire which by 
“ flicking to the Particles of Water rendered them light- 
“ er, extricates it felf from them, and afeending by its 
“ Lightnefs, the Water will become too heavy, not 
“ only to remain in this thin and light Air, but 
‘‘ even in a thicker and heavier near the Earth, and 
“ fo will be turned into a defeending DewJMifl, or Rain^ 
‘‘ or Snow, or the like, according as the watery Va* 
^ pours are either rarefied or compreffed”. 
The firft of thefe Caufes of Rain is contrary to Expe» 
rience \ for when two contrary Winds blow againfl 
each other over any Place of the Earth, the Barometer 
always rifes, and we have fair Weather. For then (as 
Dr, Halley fays, in Philofophical Tranf. No. 183) 
the Air being accumulated above, becomes fpecifically 
heavier about the Clouds, which (inftead of falling in- 
to Rain, as Dr. Nkwentyt fuppofes) afeend up into 
fuch a Part of the Atmofphere, as has the Air of the 
fame fpecifick Gravity with themfelves. 
If the falling of Rain might be attributed to the fe- 
cond of thefe Caufes, then every time a Cloud is encom- 
palfed with Air fpecifically lighter than it felf (whe- 
ther it be when by the blowing, away fome of the fupe- 
rior Air, that which is about the Qoud becomes ra- 
rer as it is lefs compreffed, or by the Cloud being dri- 
ven upwards) Rain mull neceffarily follow j whereas 
one may often fee the Clouds rife and fall without Rain, 
even when the Barometer fhews the Weight of the Air to 
be alter’d. For that happens only when by the great 
Diminution of the fpecifick Gravity of the Air about 
the 
