Ottumwa tri-weekly courier. [volume] (Ottumwa, Iowa) 1903-1916, 1905-09-07
FROST " A R N IN CSI
CLEAR STILL NIGHTS ARE THE
MOST FAVORABLE FOR
HEAVY FROST DEPOSITS.
smudse Fires One of the Best Meth
DDS of Protection Where Large
Areas Of Vegetation Are Endanger.
ed TO Protect Flowers.

Areas Of Vegetation Are Endanaer-
ed To Protect Flowers.
With the coming of cool nights and
the possibility of a killing frost, farm
ers and gardeners are figuring on the
best methods for protecting vegetation.
Inc following interesting paper on the
causes and formation of frost and. the
means OF saving garden stuff and flow
ers from injury, was recently issued
by j. M. Sherier, forcaster of the Day
export weather bureau and published
in the Times of that city:
Text books upon physics and mete-
orology teach that, in the process of
evaporation, water is converted into a
gas and remains invisible in the at
mosphere until it is condensed, when
it appears as cloud, fog, dew, frost,
etc. In the free air condensation of
the water vapor is always produced by
fall in temperature, and by this
cause only. Every one has noticed
drops of moisture trickle down the
sides of pitcher or glass containing
ice water, though it appears that not
every one is aware of the fact that this
phenomenon is due to the sudden cool
ing of the air in contact with the sides
OF the vessel to a temperature at which
the air is said to be saturated with
water vapor and condensation begins
The capacity of any space for water
vapor depends wholly upon the tenn
perature; the absolute humidity or
weight of the vapor, when the temper
ature is at 100 degrees and saturation
is complete, being about 20 times as
great as when, under similar condi-
tons, the same thermometer registers
Is degrees. The actual weight of a
cubic foot of saturated vapor at the
later temperature is 0986 grain, and
at the former temperature, 1876
grains. Hence, if air that contained 20
grains of the aqueous vapor to the
cubic foot should come into contact
witha very cold surface and be cooled
to a temperature of Is degrees, con-
densation would take place from the
time the temperature of the air was
100 degrees and moisture would be de-
posted until there would remain only
one-twentieth of the former amount of
saturated vapor, by weight, in the
same space.
Dew Is Deposited.
Dew does not fall, as we sometimes
hear stated, but is mostly deposited up
on objects in exactly the same manner
as drops of water form upon the sides
of the pitcher already referred to.
While the dew is deposited from the
air close to the cold surface, this To-
cal air receives its moisture in three
ways, viz: (1) from distant sources,
(2) by diffusion from the soil, and (3)
by evaporation from the pores on the
undersurfaces of the leaves of plants.
How Frost Is Formed.
The only difference in the condi-
lions under which dew and frost are
formed is that of temperature. 1t is
is a mistaken motion to suppose that
the thermometer must reach the freez.
ing point in the free air before the
formation of frost will begin. 1t would
be just as reasonable to assume that
drops of water would not collect upon
the sides of vessel containing ice
water until all the air in tht room had
been reduced to the temperature of
the pitcher Or glass. 1t is true, how
ever, that the surface upon which the
frost forms is at, or below, the freez-
ing point Of water, and the deposit
then takes the solid form. Frost is
not frozen dew, but the saturated va
por is condensed and CONCEALED imme
diately upon coming into contact with
the leaf, or other surface, that has be-
come cooled below the temperature of
freezing.
Frost on Clear Nights.
All exposed surfaces receive heat
from the sun during the day and radi-
ate heat into space as long as their
temperature is higher than that of the
surrounding air. After sunset, when
there are no clouds to radiate heat to
the earth and to reflect back to the
earth part Of the heat it loses, the
cooling is more rapid, and the temper
allure of objects upon which frost and
dew are usually observed soon be-
comes much lower than that of the
air short distance above the ground.
This difference is increased when the
object is exposed to a clear sky and
there is little wind to mix the air of
different degrees of warmth so that
clear still nights are the most favor
able for heavy deposits of frost, and
no frost forms on nights when there
is high wind, or when the sky it's
wholly obscured by clouds. Under
good conditions the difference in tenn
perature between the air at the sur
face of the ground and at point five
, feet above the surface of the earth
often amounts to 10 degrees, and may
be as much as 16 to IS degrees, light
frosts sometimes occurring when a
thermometer at the height of the eye
or an average sized man registers as
high as so degrees.
Where Frosts Affects.
AS rule, however, no serious dam.
| age to vegetation occurs until the in.
strument so exposed sinks to about 40
degrees. Killing frosts are likely un.
der favorable conditions, when the air
temperature is from SO to 3S degrees
On account of it's greater weight, cold
| air like watar caakc tha lowest level