( SO ) 
Air be condenfed by any internal Caufe, for Inftance, 
Cold. 
It was this Proportion, as the Author informs 
' us, that put him upon enquiring more exactly in- 
to the Nature of Dews, which by their Fall in a 
cold or condenfed Air feemed to contradid this Part 
of his Theory. The Refult of his repeated and la- 
boured Enquiries is a Dijfertation, wherein he under- 
takes to prove by a Variety of Experiments, that Dews 
do not fall, as both the Vulgar and Learned believed 
before, but rife out of the Earth. Of this we (hall 
give a brief Account, as foon as we have obferved, 
that in Proportions IX and X, he confiders what will 
happen to Vapours in any external Dilatation of the 
■ Air ; and in Propofition Xf, (hows, that in that £afe 
the Clouds are tefolved into Rain ; and upon 
this he deduces, from the two laft Propofitions, the 
Reafon of the Defcent of the Mercury in the 
Barometer in rainy Weather, and, on the contrary, 
of its Afcent in fine Weather. 
The Defign of the Dijfertation annexed , is to en- 
quire into the Nature of Dens:, explain its Ori- 
ginal and Kinds. 
' ... \ , • ", 
All Dews, according to our Author’s Philofophy, 
owe their Original either to Vegetables or terrefirial 
afcending Exhalations. Such as derive their Origin 
from Vegetables, hejtakes to be only Exudations of 
their Leaves, &c. congealed by the Air. Before he 
enters upon the Proof of thefe Pofitions, he gives us 
three general Obfervations regarding the Circum- 
ftances that are requifite, in order to have a plentiful 
Dew 
