The Emporia weekly news. [volume] (Emporia, Kan.) 1881-1889, 1889-11-28
srRANGER 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 10
the phenomena of dew and frost.
The late Professor j. Dorman Steele, in his
excellent work, Fourteen Weeks in Physics"
says: ''Dew anciently thought TO possess
many wonderful properties. Baths in this
precious liquid were said to conduce greatly
to beauty. 1t was collected for this purpose,
and for the use Of the alcheInists in their
weird experiments, by spreading feeces Of
wool upon the ground. Laurens, philoso-
pher of the middle ages. claimed that dew
was ethereal, so that If we should ill a lark's
egg with it and lay it out in the sun, imme-
diately ON the rising of that luminary, the
egg would fly off into the air! 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 1.-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,
night cools off and radiates 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 1t may be easily
demonstrated by experiment. Take an iron
ball for instance, heat it to incandescence or
until it becomes ''red hot" and then suspend
it by a wire In a little while it win part
with all its heat, and feel quite cold to the
touch. The heat has been thrown Off, it
were, or radiated, and not carried away by
the surrounding air, for precisely the same
effect will be produced il this experiment be
perfected in a vacuum. Our earth is con-
stantly -adiating its heat, like the imaginary
ball, in 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 Feii-
able Thermometer. But this point is by no
means constant or invaFiable, since dew is de
posted only when the air is saturated with
Eapor, 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.
ALI bodies have not the same capacity for
radiating heat, but some cool Inuch4Here rap
idly than others. Hence, with tue same ex-
posture, 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
larger amount of heat. This fact may also
be demonstrated by placing a black wooden
cloth and a white linen or cotton one upon
the ground over night. Grass, the leaves of
trees, wood, etc, radiate heat very freely:
but polished metals, smooth stones and cotton
cloth part with their heat more slowly, so
that the former of these substances will be
completely drenchcd with dew, while the lat
ter in the same situation. will be compare
lively dry.
The amount of dew formed on any night is
greatly influenced by the condition of the at
mosphere More dew is formed on clear even
fngs than when the sky is obscured by clouds,
because they act as shield, and reflect back
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 large deposit
of dew. But when the sky is free from clouds
the earth radiates larger amount of heat,
as there is nothing to intercept that thrown
OFF from its surface. This is the reason why
we always have colder nights'when no clouds
obscure the sky.
The formation of dew is prevented by
strong breeze, which removes the layers of
moisture resting upon the ground before they
have time to cool down to the dew point"
A slight breeze, however, is favorable to the
production of dew, as it replaces the layer of
air from which water has been deposited by
another containing more moisture. No dew
may ever be expected when the sky is OBJ
scured by clouds. or when there is a strong
sAxind
The moisture that appears upon the outside
of pitcher when it contains very cold water
IS nothing but dew. and is produced by the
same cause explained above This daInpness
frequently observed upon a cold pitcher,
even during the hottest weather in summer,
is commonly referred to by saying ''the
pitcher is sweating;" and in this simple illus
tration we permitted to recognize before
our eyes, on 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 quaint
passage in regard to Gideon's fleece. GSee
Judges vi :1-40.l-A- z Bartlett in Detroit
Free Press