form.

Sec. 2. Variation of their character at different elevations. The three
regions to which they may conveniently be considered as
belonging.

The first and most important character of clouds, is dependent on the
different altitudes at which they are formed. The atmosphere may be
conveniently considered as divided into three spaces, each inhabited by
clouds of specific character altogether different, though, in reality
there is no distinct limit fixed between them by nature, clouds being
formed at _every_ altitude, and partaking according to their altitude,
more or less of the characters of the upper or lower regions. The
scenery of the sky is thus formed of an infinitely graduated series of
systematic forms of cloud, each of which has its own region in which
alone it is formed, and each of which has specific characters which can
only be properly determined by comparing them as they are found clearly
distinguished by intervals of considerable space. I shall therefore
consider the sky as divided into three regions--the upper region, or
region of the cirrus; the central region, or region of the stratus; the
lower region, or the region of the rain-cloud.

Sec. 3. Extent of the upper region.

Sec. 4. The symmetrical arrangement of its clouds.

The clouds which I wish to consider as included in the upper region,
never touch even the highest mountains of Europe, and may therefore be
looked upon as never formed below an of at least 15,000 feet; they are
the motionless multitudinous lines of delicate vapor with which the blue
of the open sky is commonly streaked or speckled after several days of
fine weather. I must be pardoned for giving a detailed description of
their specific characters as they are of constant occurrence in the
works of modern artists, and I shall have occasion to speak frequently
of them in future parts of the work. Their chief characters are--first,
Symmetry: They are nearly always arranged in some definite and evident
order, commonly in long ranks reaching sometimes from the zenith to the
horizon, each rank composed of an infinite number of transverse bars of
about the same length, each bar thickest in the middle, and terminating
in a traceless vaporous point at each side; the ranks are in the
direction of the wind, and the bars of course at right angles to it;
these latter are commonly slightly bent in the middle. Frequently two
systems of this kind, indicative of two currents