Sacramento daily record-union. [volume] (Sacramento [Calif.]) 1875-1891, 1884-01-01

DEeeleI Oy agitation, produces q mln-
Cling of the air at different elevations,
equalizing the temperature throughout,
go the air at the earth's surface cannot be-
come much colder than the superintendent
atmosphere. Little dew, if any at all, is Pc
posted on windy nights. When the at.
mosphere is most humid, given reduction
of temperature will sooner reach the dew
point, at which the deposition of moisture
begins. An abundant dew is regarded as
an indication of approaching rain, because
it proves that the air contains large guam
| tity of vapor. Dew is not deposited on
the surface of large bodies of water whose
temperature is above 40 degrees, for as
soon as the particles at the surface are
cooled they become heavier and sink, while
warmer and lighter particles rise to the
top, by which means the surface of the
water is maintained at nearly the same
temperature as the surrounding air. In
the midst of sandy deserts, on account of
the dryness of the air, dew is almost IN.
known. Travellers upon the deserts of At
RIGA and Asia are notified of their prox.
unity to lakes or rivers by the appearance
of dew. But little dew is deposited in
cities, because most of the objects there
found are stronger power radiators than the
leaves of vegetables, and because the heat
of the city is always greater than that of
the surrounding country.
THE FORMATION OF FROST.
Hoar. frost is formed under the same cir.
cumstances as dew, with the exception
of lower temperature. When the tenn
perature of plants falls below 80 degrees
the moisture of the air is condensed upon
them in the solid state, and forms layer
of spongy ice. Hoar.frost is, therefore,
net frozen dew, but the moisture of the air
is deposited in the solid form, without hav-
| ing passed through the liquid condition.
Hoar- frost, like dew, is deposited chiefly
upon those bodies which radiate best,
such as plants and the leaves of vegetables.
Since plants sometimes become cooler by
radiation from u to Is degrees below the
temperature of the air, frost may occur
although a thermometer a few feet above
the ground does not sink to 80 degrees.
During a clear and still night, when Their
mometer nix feet above the ground sinks to
Sc degrees, very heavy frost may be ex-
pected, and slight frost may occur when
the same thermometer sinks only to AZ de-
grees. During cold nights of spring,
plants which are sheltered by trees are
less liable to be injured by frost than those
which are fully exposed. a thin covering
of straw will generally afford entire pro-
lection. A garden may frequently be
saved from injury by kindling fire, which
will envelop the plants in cloud of smoke.
Fogs and clouds also protect vegetItion
from the effects of frost. Plants are often
killed by frost in the valleys and up to
certain hight upon the hills, while above
this limit they entirely escape injury. 1t
has been found by observation that Their
mometar attached to high tower in val
ley indicates at night the same average
temperature as thermometer ON the side
of a hill upon the same level. This indi-
Gates that during tranquil nights cold air
resulting from radiation at the surface of
the earth settles in the valleys in conse-
quence of its greater density, and the
warm and cold air are arranged in nearly
horizontal strata, like liquids OF different
densities.
SOMETHING ABOUT FOG.
The vapor in the atmosphere ia nearly or
quite transparent, but when, from any
cause. the air becomes cooled below the
dew point, portion OF its vapor is precipi-
tated in the form of drops of water ex.
tremelv minute, which affects the transpa-
rency OF the air and forms fog or cloud,
according as it occurs near the surface of
the earth or in the upper regions of the at
mosphere. When steam rises from vessel
of warm water and mingles with cold at
mosphere, portion of the vapor is con-
densed and mist is formed. This mist is
sometimes, but improperly, called vapor.
Vapor of water is gaseous body, while
mist is liquid body. a similar condensa-
ton often takes place in nature upon a
large scale, and the mist ia then called fog.
Fogs are most prevalent near the banks Of
Newfoundland. These fogs occur in every
month of the year, but they are most fire.
quent in summer, when the banks are en-
veloped in fog nearly half the time. The
vapor which causes these fogs is furnished
BY the warm air of the Gulf Stream, which
is condensed by the cold air Of the banks,
the contrast of temperature being here
more sudden than is found in any other
part of the Atlantic ocean. During July
the water on the banks frequently has
temuerature Of 40 degrees, while within
distance Of less than 300 miles the Gulf
Stream has temperature Of IS degrees.
The contrast in temperature is almost
equally great in January, but fogs are less
frequent in winter, because at that period
the air is more agtated by storms, which
tend to equalize the temperature over diff
ferent parts of the ocean.
OCCASIONAL DRY FoGs.
In the United States dry fogs frequently
occur in November, or the latter part of
October. This period is commonly known
as Indian summer, and is characterized by
a hazy condition of the atmosphere, red
ness of the sky, absence of rain, and mild
tempers ture. This results from a dry and
stagnant state of the atmosphere, during
which period the air becomes filed with
dust and smoke arising from numerous
fires, by which its transparency is greatly
impaired. This phenomenon is not peculiar
to the United States, similar condi-
ton Of the atmosphere being frequently
observed in central Europe. These fogs
have been ascribed to the presence of fine
volcanic ashes in the air. In 1888 such
fog prevailed over all Europe, and contin-
ned for more than = month. 1t was pre-
coded by remarkable eruption of Mount
Hecla, in Iceland, which for long time
emitted smoke OF unu nal density. In
1881 similar fog prevailed in the United
States, in Europe, and on the coast OF
Africa. III OOsCurel Jhe air 10 sdcn an eX-
tent that the sun could be observed all day
with the naked eye, without the interposi.
ton OF any colored glass, Alright the fog
seemed decidedly phosphorescent, and
emitted an appreciable amount Of light
which could not be ascribed to the reflected
light of the stars.
HOW RAIN Is PRODUCED.
The origin of rain is from the conden-
sation Of a portion of the vapor in the air
which forms a mist or cloud, Generally
this condensation proceeds slowly, and the
clouds which result do net furnish rain.
When this condensation takes place with
sufficient rapidity, the small particles of
mist increase in diameter by the condensa-
ton of more vapor, and forming drops of
considerable size, descend to the earth in
a shower of rain. Rain is the condensed
vapor Of the air, and this condensation can
only be caused by cooling the air below the
temperature OF the dew point. This re-
duction of temperature may be affected by
radiation, or by the contact of warm air
with the cold surface of the ground, espe-
cialy the surface OF mount ins, or by the
minglng OF warm air with colder air.
These processes are so gradual, or limited
in extent, they probably never result III