in winter, the N. W. wind in large volume has elevated the
trade very high. Condensation is not necessarily in form of visible cloud.
It may be of that smoky character which sometimes attends mid-summer
drouths, giving the sun a blood-red appearance; or it may be like that
change from deep azure to a "lighter hue," obscuring the vision, which
Humboldt describes as preceding the arrival of the inter-tropical belt of
rains. Gay-Lussac, and other aeronauts, have seen a thin cloud stratum at
the height of 20,000 to 30,000 feet, not visible at the earth, although
some degree of mistiness and obscurity were observed. At that elevation
the clouds are thin, and always white and positive. Some degree of
turbidness is frequent; it may occur, as we have stated, with N. W. wind,
but, if it does, the wind soon changes round to the southward.

This turbidness or mistiness, where it exists, and indicates rain, does
not disappear toward night, as it should do if but the daily cloudiness
which results from ordinary diurnal magnetic activity, but becomes more
obvious at nightfall; and, when hardly visible at mid-day, or during the
afternoon, may then be observed, obscuring in a degree, the sun's rays;
and, later in the evening, forming a circle round the moon. Thus Jenner--

"Last night the sun went _pale to_ bed,
The moon in _halos_ hid her head."

And so, too, Virgil--

"The sun, too, rising, and at that still hour,
When sinks his tranquil beauty in the main,
Will give thee tokens; certain tokens all,
Both those that morning brings, and balmy eve.

* * * * *

When Sol departs, his mighty day-task done,
How varied hues oft wander on his brow.

* * * * *

If the ruddy blaze
Be _dimm'd_ with _spots_, then all will wildly rage
With squalls and driving showers: on that fell night
None shall persuade me on the deep to urge
My perilous course, or quit the sheltering pier.
But if, when day returns, or when retires,
_Bright_ is the orb, then fear no coming rain:
Clear northern airs will fan the quiv'ring grove.
Lastly, the sun will teach th' observant eye
What vesper's hour shall bring; what clearing wind
Shall waft the clouds slow floating--what the South
Broods in his humid breast. Who dare belie
The constant sun?"

More frequently this kind of condensation is sufficiently dense at
night-fall to take shape,