The National tribune., 1890-03-13

The Appearance OF the sun in Giving Local Indl
cations Of the Weather.
BY LIEUT.. J. ?. FINLEY, U. :. SIGNAL SERVICE


BY LIEUT.. J. +. FINLEY, L. :. SIGNAL SERVICE.
Correspondence invited suggestions desired
and information chccrfuIiy furnished. Every cf-
fort employed 10 make this Bureau Of practical
10 the readers Of THE %ATIOSAL THIhtNT All
communications should be addressed lPcnHler
THE &ATIoEAL TRIBUNE Office Washington. u. C.
Since the coOrs aud duration of twilight.
especially at evening, depend upon the amount
Of condensed yapor which the atmosphere con-
taius, these appearances should afford some in
dicationa Of the weather which may be OK
pccted TO succeed. If there were no atmos
phere. night would commence rs soon as the
sun dcsceud5 below the horizon, and the day
would begin with equal abruptness The astro.
nOmical lmit Of twilight is generally understood
10 he the instant when stars Of the 81 xti magni-
tudc begin 10 be visible ia the zenith nj evening
or disappear 10 the morning. In our climate the
evening twilight generally terminates when
the sun is IL or lS' below the horizon. Tho
morning twilight commences at Il somewhat
less DEPRESSION since the yapOr Of the atmos.
phcre condensed during the night does not rise
to SO great hight inthe morning rs at evening.
These limits. however, are variable, the dGra-
ton Of twilight depending upon the state OF
the atmosphere When the sky Is of pale
color, indicating the presence Of an unusual
amount Of condensed yapor, twilight il OF
longer duration. This happens habitually In
the polar regions. On the contrary, within the
tropics, where the air is pure and dry twilight
sometimes lasts only ID minutes When the
sun is still 10 below the eastern horizon the
latter generally appears bordGrGd with rcd or
orange band, above which the twilight curve
rises about 70. The orange zone gradually
extends, becomes bOrdered with yellow and
afterward with green, while the light curve
asccuds toward the zenith. When the sun is
only 2 below the eastern horizon, the latter
| becomes yellow, the green zone becomes more
decided, aud extends from 30 TO l8s, the twi-
| light curve extends 10 within % Of the western
horizon, and is b0rdercd with q purple zone
about 10 in breadth. AS the sun rises tho
western horizon appears bordercd with Il rosy
band surm0unted by yellow. The red in the
east disappears, and is succeeded by yellow
surmountcd by green, which continues after
the yellow has disappeared whom the sun is 20
or 4" above the horizon.
The red and yellow zones arc ascrbed TO the
absorption produced by the different thick
ncsses Of air trayersed by the rays OF light.
The green color results from a combination of
the yellow rays with the blue rays of difluse
light, reflected from the PARTICLES Of the atmOs-
pherc green being produced by mixture Of
yellow aud blue
When, after sunset, the western sky Is Of a
whitish yellow, and this tint extends to a great
hight, il is probable that rain will occur during
the night or the next day. Candy or unusual
hues, with hard, definitely outlined clouds,
lolCtcII ram ana pIoDaDly VIVA. ii the sun,
before setting appears ditiuse and of "a brilliant
white, it foretells a storm II il sets in sky
slightly purple the atmosphere near the ze-
NTH being of bright blue, we may rely upon
fine weather. A red sky in the morning pre-
sages bad weather, or much wind, if not rain
but If the sky presents simply rosy or gray
ish tint, we may expect fair weather
Rays Of the sun appearing in a cloud called
sun drawing water" forebode rain. This
phenomenon is, in fact caused by the image of
the sun being reflected in an intervening cloud,
the reflected image radiating in the cloud
Ayers sarsaparilla will remove that tired