of wind, at different
altitudes intersect one another, forming a network. Another frequent
arrangement is in groups of excessively fine, silky, parallel fibres,
commonly radiating, or having a tendency to radiate, from one of their
extremities, and terminating in a plumy sweep at the other:--these are
vulgarly known as "mares' tails." The plumy and expanded extremity of
these is often bent upwards, sometimes back and up again, giving an
appearance of great flexibility and unity at the same time, as if the
clouds were tough, and would hold together however bent. The narrow
extremity is invariably turned to the wind, and the fibres are parallel
with its direction. The upper clouds always fall into some modification
of one or other of these arrangements. They thus differ from all other
clouds, in having a plan and system; whereas other clouds, though there
are certain laws which they cannot break, have yet perfect freedom from
anything like a relative and general system of government. The upper
clouds are to the lower, what soldiers on parade are to a mixed
multitude; no men walk on their heads or their hands, and so there are
certain laws which no clouds violate; but there is nothing except in the
upper clouds resembling symmetrical discipline.

Sec. 5. Their exceeding delicacy.

Secondly, Sharpness of Edge: The edges of the bars of the upper clouds
which are turned to the wind, are often the sharpest which the sky
shows; no outline whatever of any other kind of cloud, however marked
and energetic, ever approaches the delicate decision of these edges. The
outline of a black thunder-cloud is striking, from the great energy of
the color or shade of the general mass; but as a line, it is soft and
indistinct, compared with the edge of the cirrus, in a clear sky with a
brisk breeze. On the other hand, the edge of the bar turned away from
the wind is always soft, often imperceptible, melting into the blue
interstice between it and its next neighbor. Commonly the sharper one
edge is, the softer is the other, and the clouds look flat, and as if
they slipped over each other like the scales of a fish. When both edges
are soft, as is always the case when the sky is clear and windless, the
cloud looks solid, round, and fleecy.

Sec. 6. Their number.

Thirdly, Multitude: The delicacy of these vapors is sometimes carried
into such an infinity of division, that no other sensation of number
that the earth or heaven can give is so