Rock Island Argus. (Rock Island, Ill.) 1893-1920, 1905-08-31
i'm. SHERIER WRITES OF FROST;
LIGHT ON EVERY DAY Phenomena
Weather Though Much Discussed, Apparently Little
Understood, Even in its Simplest Features
Rap at the Long Range Man.

itAt DOOhS upon physics anu metz
orolgy teach that, in the process of
evaporation, water is converted into
d gas and remains invisible in the at
mosphere until it is condensed, when
il appears as cloud, fog, dew, etc. In
the free air condensation Of the water
yapor is always produced by fall in
temperature, and by this cause only.
We all of Us have noticed drops of
moisture trickle down the sides of a
pitcher or glass containing ice water,
though it appears that not every one
is aware of the fact that this phenom-
enon IS due 10 the sudden cooling 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 yapOT and condensation begins.
The capacity Of any space for water
vapOT depends wholly upon the TEN
peTature, the absolute humidity, or
weight of the vapor when the temper
AZURE is at 100 degrees and saturation
H. complete, being about twenty times
a. great as when, under similar con
dItiOEs, the same thermometer regis
tcrs , degrees. The actual weight of
a cubic foot of saturated vapor at the
latter temperature is O-9SG grain, and
at the former temperature, 1896
grains. Hence, if air that contained
20 grains of the aqueous vapOr TO the
cubic foot should come into contact
with a very cold surface and be cooled
To temperature OF - degrees, con
dcnsation 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
une-twentieth of the former amount
of the saturated vapor, by weight, in
the same space
Dew Does Not Full.
Dew does not fall. as We sometimes
hear stated. but is mostly deposited
upon objects in exactly the same man
Her as drops of water form on the
sides of the pitcher already referred
TO- While the dew is deposited from
the air close to the cold surface, this
local air receives its moisture In three
ways, viz; Cd from distant sources
t2Dby diffusion from the soil. and (3}
by evaporation from the pores on the
und "rsurfaces of the leaves of plants
The only difference in the condi.
tious under which dew and frost are
formed is that of the temperature
II is mistaken notion to suppose
that the thermometer must reach the
freezing point in the free air before
the forHtatiOn of frost will begin. II
would be just as reasonable to assume
that the drops of water would not col
IeCt upon the sides of a vessel con
I;
the TTy6fn had been reduced to the TEN
peraturc of the pitcher or glass. 1t is
true. however. that the surface upon
which the frost forms is at or below
the freezing point OF water, and the de
post then takes the solid form FrOs'
is NOT frozen dew. but tho saturated
VapOr is condensed and CONCEALED ina
me liately upon coming iato contact
with the leaf or other surface. thai
has become cooled below the tempera
tuTe of freezing
Receive and HadIntc Heat.
All exposed surfaces receive heal
from the sun during rhe day and radi
ate heat into space as long as theii
temperature is higher than that of the
surrounding air After sunset. wher
there are no clouds To radiatc heat &c
the earth and 10 reflect back to the
earth a part OF the heat IL loses. the
cooling is more rapid and the tempera
turo Of objects upon which frost anc
dew are usually observed soon becomes
much lower than that of the air shor
distance above the ground This diff
ference is increased when the ObjeC
is exposed 10 a clear sky and there Il
little wind 10 mix the air of differen
degrees of warmth. so that clear still
nights are the most favorable for heav
deposits of frost. and no frost forms o
nights when there II a high wind. O
when the sky il wholly obsCuTed b
clouds Under good conditions the di
ference in temperature between tn
air al the surface Of the ground and a
a point tive feet above the surface q
the earth often amounts To 10 degrees
and may be as much as 10 10 j. d'
Erees light froStS sometimes oCcurrin
when a thermometer al the height [
the eye OF an average sized man regis
tiers As high as - degrees. But. as
rule. no serious damage 10 VeSetauo
occurs until the instrument 50 {,
posed sinks To about 40 degrees HI
ling fTosts are likely. under fByOrabl
conditions. when the air temperatur
Is from ST to IS degrees. On acCOuT
of its greater weight cold air like VI
ter seeks the lowest level. while ID
air that y displaced rises until
reaches an elevation where the densit
is equal 10 ats own. For this reason
is always coolest in valleys on SIT
nights and is warmest on the tops ,
rather low hills Fruit trees and othe
vegetation planted upon expose
slopes. and that appear to occupy
bleak position. thus often escape injuI
NJ times when similar trees and PLAN
in the valley. seemingly much bett,
sheltered, are seriously damaged.