126 Mr. Colebrooke’s Meteorological Observations 
the lower, close to the sea’s surface. The weather was at this 
time nearly calm, and the atmosphere unusually dry. 
Confined air, environed by moisture, becomes fully saturated 
with it. Not so, unconfined air, even upon the face of the sea. 
Were the atmosphere over the high seas, or the inferior strata 
of it constantly saturated, or nearly so with humidity, a fog or 
mist would be perpetually hanging upon the face of the ocean, 
or low clouds be suspended over it. A serene sky, or a clear 
sea, would scarcely occur. The air is generally damper on sea 
than on land; but not approaching to saturation. 
According to the observations made by me, the degree of 
dryness within the limits of the trade-winds, was ordinarily 
about 4° or 5°, implying nearly a sixth part wanting to satura- 
tion. It seldom descended below 3°; but often rose to 6° and 7°, 
and sometimes to 8° and even to 9°; which extreme point im- 
plies, at the temperature attending it, nearly a third part wanting 
to saturation. 
The mean dryness in the range of the trade-winds, may be 
taken at 4° to 5°, attended by temperature from 68° at the 
furthest limit of their influence, to 82° at their nearer confines. 
Between the lower strata of the atmosphere which may be 
hygroscopically examined, and its upper strata, the hygrometric 
condition of which is but to be conjectured from the appear- 
ances put on by clouds in them, continued interchange is going 
on, by reason of evaporation, as well as in consequence of un- 
equal temperature. Warm humid air ascends; cool or dry 
air succeeds to it. 
Whether it be heat or humidity, or both, by which air is ren- 
dered specifically lighter, it must from its levity, rise in the 
atmosphere and give place to other, which is heavier. | Dry air 
rushes to replace moister, in like manner as cold air does soto take 
the place of warmer; that is, in both cases, denser instead of 
that which is less so. The one, which comes in place of the 
other, may be both drier and colder than that to which it succeeds, 
or it may be heavier only by the difference of the excess of one 
quality above the defect of the other. It may be drier and 
