Sacramento daily record-union., 1882-01-25
METEOROLOGICAL,
Interesting Statement about the Forma-
ton Of Ice, Frosts, Dew. Etc.

tion of Ice, Frosts, Dew. etc.
Sergeant james A. Barwick, of the United
States Signal Corps at this station, having
bsen questioned several times why it is, when
the report of his thermometers indicate a
temperature considerably above the freezing
point. that frost and ice often forms on the
surfsce of objects near or on the earth, makes
the following interesting and instructive
statement upon the subject:
The phenomena mentioned is caused by
radiation of heat. All bodies on the sarface
of the earth send out rays of heat toward the
| sky. and when they radiate more heat than
they receive their temperature falls below
that of the surrounding air. In order TO
study these effects, we place number of
thermometers upon the ground on substances
of different kinds, and suspend thermo-
meters in the air at various elevations, and
compare the readings Of these thermometers,
simultaneously at all hours of the day and
night. Very careful observations of this kind
were made at Greenwich, England, for two
years. It was found that q thermometer
placed on grass fully exposed to the sky fire.
quently sinks ten degrees below thermometer
suspended four feet from the ground. On
nine nights the difference of temperature was
more than Is deg, and in one instance a
thermometer placed or raw wool sunk 70 deg.
5 min. below one suspended eight feet from
the ground. Whatever prevents the free ex-
posure of an object to the sky causes the
temperature to decrease less than It would IT
the exposure was complete.
This effect is produced by spreading sheet
of cloth over the ground, even though it be at
considerable elevation. The thinnest cam
bric handkerchief produces a decided effect.
Trees and buildings and whatever conceals
a part of the sky, diminishes the effect of the
radiation of heat from the surface OF the
earth. Clouds produce the same effect as an
artificial covering A thermometer placed
on grass fully exposed to the sky sunk below
Thermometer suspended four feet from the
ground, as follows: On cloudless nights, 9.3
deg. nights half cloudy, 7.3 deg; nights
principally cloudy, 6S deg; nights entirely
cloudy only "a deg. By suspendiDg ther-
mometers at different elevations above the
earth. from one or two inches up to 200 feet, it
is found that the loss of heat by nocturnal
radiation is quite sensible at 80 feet, and
does not entirely disappear at the hight of
100 feet. During the night, therefore, the
temperature of the air increases as we rise
above the earth's surface. If Thermometer
placed on grass fully exposed to the sky be
taken as the zero, a thermometer one inch
above it would read 8 deg. higher; six inch
es, 8 deg; one foot, deg; twelve feet, s
deg; fifty feet, 10deg.; one hundred and fifty
feet, II deg. The effect is apprecisble at still
greater elevations.
The Signal Service thermometers are thir-
tyseven feet from the ground; therefore our
Thermometer should read about 8 deg.
higher than thermometer on grass at the
earth's surface. Ice should commence to
form in places fully exposed to the open sky
when our thermometer would read IS or 40
deg, which is generally the case, unless the
air is very dry. After few days Of north
winds, freezing would not take place at the
earth's surface at temperature Of 40 deg.
by the Signal Service thermometer, because the
temperature of the grass or other substances
would have to be reduced before they reached
that point at which dew or hoar-frost would
be deposited; while with more moist air
there would be ice and frost formed, when
the thermometer would not indicate as low a
temperature. That is why our cold north
winds are not so damaging to semi-tropical
plants and shrubs, for the temperature must
get down to that point at which the moisture
in the air could be condensed.
1t must be thoroughly understood that
dew and frost do not fall like rain, but they
deposit on all substances whose temperature
falls below the dew point of the air, and the
lower each substance falls, the heavier will be
the dew or frost deposited Any substance
that gives off heat more rapidly into space
than it absorbs it from the earth, the quicker
it reaches the dew point; which accounts for
some objects, such as glass, exposed to the
open sky of damp nights, being
drenched in dew, while polished piece of
iron will scarcely be dimmed. The iron
receives heat from the earth faster than it ra-
dates it into space aud its temperature is
longer reaching the dew point, while the
glass gives off heat by radiation very much
faster than it absorbs it from the earth; it
therefore falls considerably below the dew
point Plants are not covered up to prevent
frost from falling upon them, but to prevent
them from throwing off or radiating their
heat received during the day, and also at
night from the earth's radiation; it being pre-
vented, the tree does not cool below the dew
point, therefore no frost is deposited. Hoar-
frost is formed under the same circumstances
as dey, with the exception of a lower tenn
p rature.
When the temperature of plants falls be-
low 80 deg. the moisture of the air is con-
densed upon them in the solid state and forms
a layer of spongy ice. Hoar-frost, like dew,
is deposited chiefly upon those bodies which
radiate heat best, such as plants and the
leaves of vegetables. The deposits is principally
on those parts which are turned toward the
by radiation from II to IL deg. below the
temperature of the surrounding air, frost
may occur, although a thermometer few
feet above the ground does not sink to 80 deg.
During clear and still night, when a ther-
mometer six feet above the ground sinks to
SO deg very heavy frost may be expected,
and slight frost may occur when the same
thermometer sinks only to AZ deg.
u L. 1t.
has been quite bountiful in some parts of the
State, ceased here yesterday morning, with a
total for the storm of only .2S of an inch
The report from the Signal Corps headquar-
ters last evening showed the barometer to be
falling at Olympia. Portland and Los An
geles, with fresh south wind at Olympia,
northwest and fresh at Portland and fresh at
Los Angeles. 1t was raining at Olympia, Los
Angeles and San Diego, and the barometer
was rising at all the other stations, with
northwesterly and westerly winds generally
prevailing up and down the coast. The rain
fall for the past twenty-four hours at Olym-
pia was .16 of an inch; /; Portland, OIL Rose
burg, .02; Red Bluff. .06; Sacramento, .16
San Francisco, II; Visalia, Al; Los An
geles, 81 f; San Diego, .06.
A MAMMOTH ScREEN.-A bulletin-board
of immense proportions, 290 feet long and
40 feet high, is to be erected along the south
side of the alley between H and 1, Second
and Third streets. The parties who purpose
the building of this boss bulletin. board Sc
cured the right to construct and maintain the
same for five years for 1915. Whether it is
to be used as a plaque for esthetic disciples to
decorate with buiIrushes, broken lilies and
long-legged storks, or by some entsrprising
merchants for advertising purposes, or as a
screen to hide the filth of Chinatown, has
not as yet been ascertained. But whatever
its purpose, it will serve to hide from public
view an at present very unattractive rear view
of quarter that smells in the public nostrils
and is an ofense to the eye.
HoUsEBREAKING "A thief entered the
store.room of F. w. Fratt, on ] street, be-
tween Third and Fourth. Sunday night, and
stole two large mirrors. There was large
quantity of other material in the room which
was net disturbed. An entrance was eff.
fected by breaking in at the back door. The
mirrors were marked so. H" on their backs
with paint.
COMMERCIAL steamer Governor Dana
arrived last night from Jacinto with full
barge load of wheat, besides merchandise per
steamer. A large amount of freight, includ-
ing wool, is now being shipped below by the
bay steamers each day, and the freight busi-
ness generally is quite lively,