The National tribune., 1890-08-28
THE WEATHER.
Cloud Observations.
by LIEUT. j. r. FINLEY, U. $. SIGNAL SERVICE.

Correspondence invited, suggestions desired,
and Information checrfuiy furnished. Every ef-
tort employed to make this Bureau of practical
to the readers of THE NATIONAL FHInUNE. All
communications should be addressed Weather
TIE NATIONAL TRIBUNE Office Wnshingtou ID. g. |
Clouds are the embodiment of wind currents,
and from their fern and manner of develop
ment much can be gained to aid the observer
IN making local weather forecasts. Even the
student OF the weather map who is engaged in
u general study of the whole country can OBJ
tain much important information from his
cloud map to help in forming q correct judg-
ment as to the probable weather conditions
over large regions. Variations in temperature
are greatly influenced by the presence of clouds
If clouds arc heavy and continue throughout
tho day, the temperature changes but very
little, with q tendency to grow warmer. The
large amount of condensed vapOr in the air
prevents radiation from the earth into space,
and therefore the heat that has accumulated
near tho earth and in the surface soil IS held
there. This is the condition in Summer. In
Winter c!oudiness prevents increase Of cold by
checking radiation aud increase of heat by
cutting oil the sunshine therefore the temper
atnro remains nearly stationary.
In the study Of clouds 10 Is very important
to note the class TO which they belong, the
direction from which they are moving and
when practicable their velocity of progression
by reference 10 some fixed point. In order to
secure absolute accuracy the observer should
make the cloud observation with his head
steadicd by a fixed object.
The direction Of the movement is more easily
observed through slightly colorcd glass. espoci-
ally in the case Of dense clouds during the
day. The colored glass not only protects the
eyes from the glare of bright liglrt, but also
aids in bringing out in bold relief the finer
portions Of clouds, and assists in detecting the
presence Of worry fine cirrus, not visible to the
naked eye.
The following are the different classes of
cloud formations recognized by tho United
States Weather Bureau. They are divided
according to elevation, into upper and lower
clouds. Tho former are cirrus, GIRO cumulus
and cirrO. The latter are nimbus, Gu
muo-stratns, stratus, aud eumuIus. Scud, fog
haze, aud smoke may be classed as lower cloud
formations, as they affect the condition of the
lower atmosphere. The cumulus may be either
upper or lower, depending upon their relative
elevation above the surface OF tho earth. MANY
cloud formations may gradually merge into
each other, and the line Of demarcation be
quito difficult TO define. The cirrus is the
highest cloud observed, and is of the least
density. II Is seldom less than five miles, and
often ten miles in elevation. The cirri are
defined as parallel, flox ious. or divCrging fbers
oXtensible by increase in all directions They
arc supposed TO be composed of minute spiCglB
OF ice or snow crystals floating in the at mo-
sphere, as II Is only during their presence that
the phenomena Ol parhelia aud halos arc OBJ
served. They observed in a great variety
OF shapes aud appear IN u thin ibrous texture
or a feathcry, hairy formation, often grouped
in cnrlcd brushes or ilaments, diycrgiug 10
the ends rs If electrified.
The GIRO. cumuli arc small, .wcll-defined
rouudish masses, in close horizontal arrange
N.a..s 80. .F-s..F "a. d L.
ton of the cirri, and arc next below them in
elevation. Observations OF these clouds are
especially useful in indicating the approach of
rain AS "a rule, rain will follow in from II to
24 hours after their appearance. especially If
the clouds are we'll developed.
The cirIo-stratus appear 10 be tho result of
the cirrus descending to a lower level thickcn-
ing by additional matter, and the gradual
change from the frozen state 10 the yapOr FORM
Their elevation varies from that of the low
cirrus down to the position of the stratus
clouds. Especially IN the vicinity of bodies
of water, the GIRO stratus will gradually fall
and thclien into stratus clouds.
The cumulus appears in convex or cOnical
heaps, increasing upwards from "a horizontal
base. They are usually formed in the strata
of lower base clouds, aud vary in size from
a few rods TO several miles in thickness. The
position of the horizontal base of the cumulus
approximately defines the point above the
earth where the dow-point is equal to the tenn
pGraturo OF the air.
Tho eumulostratus is formed by tho blond
ing of the cirro-stratus with the cumulus, either
appearing intcrmiXed with the heaps of the
latter or superadding a widespread structure
to its base. They are usually of darker
color than the Cumulus, and when well de-
voloped mark tho approach of thunderstorm.
The stratus is the lowest OF clouds, aud when
ii extends to the earth is called fog lt geuer-
ally forms thick vail OF vapor of dark color.
The nimbus is any cloud or system of clouds
from which rain or snow is falling The scud
is an individual cloud moving rapidly at a low