Rock Island daily Argus. (Rock Island, Ill.) 1886-1893, 1889-11-22
LITTLE DROPS OF DEW.
THE TRUE THEORY OF THEIR ORl-
GIN AND OTHER FACTS.

Curious Phenomena They Exhibit and Er-
roneous Ideas Concerning Them-won-
dcrfui Productions Of Nature That Puz-
zied the Ancient Philosophers.
To the ancient philosophers the appearance
of dew and frost was a complete mystery, and
numerous were the theories advanced, by
those scientifically inclined, to account for
their production, and the interesting phe-
nomena they presented. Many, it is said, be-
lieved that the dew was nothing else than the
tears shed by the Almighty upon our earth,
and they regarded it a sacred substance
that possessed a number of wonderful and in
explicable properties. They also attributed
10 IL many strange events and curious mani
festations that occurred In those times, and
some rubbed il over their bodies in order to
protect themselves from the evil spirit, whose
malignant influence was held responsible for
all the marvellous and unaccountable opera
tions OF nature observed in the earth and the
heavens above.
STRANGER THAN FICTION.
Among all the numerous truths stranger
than fiction that the study of natural sci
ence has revealed, there are few more inter
eSting and instructive than those relating to
the phenomena Of dew and frost.
The late Professor j. Doriuan Steele, in his
excellent work, Fourteen Weeks in Phvsics, -
says; Dew was anciently thought TO posses
many wonderful properties Baths in this
precious liquid were said to conduce greatly
To beauty. Ii was collected for this purpose
and for the use of the alchemsts IN their
weird experiments, by spreading fieeces of
wool upon the ground Laurens, a philoso
pher of the middle ages, claimed that dew
was ethereal, so that il we should ill lark's
egg with it and lay 1t out in the sun, imme
dately on the rising of that luminary, the
egg would fly off into the arl This expert
ment is best performed with goose's egg"
There is considerable misapprehension
among the general public concerning the ma
ture and origin of dew and frost, it being
commonly supposed by the great majority of
people that dew actually falls from the sky,
and how frequently do we hear the ex.
preston ''the dew is falling fast" The fact
is, dew never falls, but is formed on the sur
face of the earth, and always at the identical
place where it is seen by the observer Dew
is simply the moisture of the air condensed by
coming in contact with objects upon the
ground that are colder than itself The earth,
heated during the day by the suns rays, at
night cools Off and radiates a considerable
portion of its heat into space. All bodies left
TO themselves, will gradually become cool If
previously heated This is termed in natural
philosophy, radiation, and it may be easily
demonstrated by experiment. Take an iron
ball for instance, heat it TO incandescence or
until il becomes ''red hot, and then suspend
it by wire. In "a little while it will part
with ali its heat, and feel quite cold to tine
touch. The heat has been thrown OFF as it
were, or radiated, and not carried away by
the surrounding air, for precisely the same
effect will be produced if this experiment be
perfected in vacuum. Our earth is con
stantly radiating its heat, like the imaginary
ball, i'll all directions, and at night becomes
so cool that the invisible vapor resting
upon its surface is condensed into water
and deposited as dew The temperature at
which this takes place is called the dew
point" as indicated by an accurate and reli-
able thermometer. But this point Is bv nc
means constant or invariable, since dew is de
posted only when the air is saturated with
vapor, and the amount of moisture required
to saturate air of high temperature Is much
greater than for air CT low temperature.
LIKE THE SWEATING" PITCHER.
All bodies have not the same capacity for
radiating heat, but some cool much more rap
idly than others. Hence with the same ex
posure, some bodies will be covered densely
with dew, while Others will remain perfectly
dry. Dark objects have more dew deposited
upon them than light ones, because they are
better radiators, and, therefore, part with a
larger amount of heat This fact may alsc
be demonstrated by placing a black wooler
cloth and white linen or cotton one upon
the ground over night. Grass, the leaves OF
trees, wood, etc, radiate heat very freely
Ng-A.. -.
cloth part with their heat more slowly, sc
that the former Of these substances will be
completely drenched with dew, while the lat
ter, in the same situation. will be compare
lively dry.
The amount of dew formed ON any night i
greatly influenced by the condition of the at
mosphere. More dew is formed on clear even
ings than when the sky is obScured by clouds
because they act shield, and reflect bach
the heat radiated by the earth into space be
sides furnishing that received by them dur
ing the day, which prevents the earth from
cooling OFF enough to produce a large deposit
Of dew. But when the sky is free from cloud.
the earth radiates larger amount OF heat
there is nothing TO intercept that thrown
OFF from its surface. This is the reason why
We always have colder nights when no cloud.
obscure the sky.
The formation OF dew is prevented by 9
strong breeze, which removes the layers OF
moisture resting upon the ground before they
have time to cool down 10 the 'dew point
A slight breeze, however, is favorable to the
production Of dew, as il replaces the layer OF
air from which water has been deposited by
another containing more moisture. No dew
may ever he expected when the sky is OBJ
scured 10y clouds, or when there Is a strong
wind
The moisture that appears upon ths outside
Of II pitcher when 1t contains very cold water
is nothing but dew, and Is produced by the
same cause explained above. This dampnes,
frequently observed upon a cold pitcher,
even during the hottest weather in summer,
is commonly referred to by saying 1.-THE
pitcher is sweating;" and in this simple illus
tration we are permitted to recognize before
our eyes, on a small scale, the same interest
| ing process of dew formation that takes place
over the surface of the great earth. Dew is
alluded TO in the writings Of many ancient
philosophers, and the Bible contains O quaint
passage in regard to Gideon's fleece (See
Judges vi S7-i0.l-A- < Bartlett in Detroit