SOILS, MANURES, &c. 259 
obtain it: in fuch climates the very exig¬ 
ence of plants, in all probability, depends 
on them. 
It is difficult to define what are the 
component parts of dew, or to inveftigate 
S 
its peculiar properties; there can how- 
ever be no doubt, that it is produced 
• principally by exhalations from the earth, 
which when condenfed by the cold air of 
*» ' ! 
the night, become fpecifically heavier 
than the atmofphere, and defcend again 
to the earth, or upon any objeft they 
meet with. 
The particles of dew certainly confift 
principally of water; it is, however, 
probable that they contain a minute 
proportion of volatile alkali, attrafting 
and uniting with the nitrous acid of the 
air, whereby they fooner become con¬ 
denfed and fpecifically heavier than fuch 
exhalations as afcend higher in the 
O 
atmofphere. 
