The Anderson intelligencer. [volume] (Anderson Court House, S.C.) 1860-1914, 1881-01-20

grass OSCOtIiGS Wtb tNclI UCloIo -t0eN-Sou
has set. Hence, also, We find the grass
in the morning, when the atmosphere is
moist, perfectly drenched with dew, pro-
yided the preceding night has been
clear and still. On the other. hand. in
drought, the grass is;freqaently 50 dryin
the early morning that we may walk in
tat will without dilnming the polish Of
our boots.
(2) Another modifying circumstance is
the clearness of the heavens. Clouds
refect.back the radiant heat and prevent
the necessary reduction ofstemperature:
The most oppressive nights in summer
are generally cloudy nights. The radiant
3 heat is not thrown off and lost in free
space, but is thrown back to the earth by
the clouds, and hence the sultry, suffo-.
eating Feeling we experience on cloudy
summer nights. Take certain weight
of wool and lay it on the brass at sunset,
and stretch three or four feet above it on:
uprights thin piece of cloth. Place
near by on the grass, but unprotected,
an equal weight of wool, and on each
parcel put a thermometer. On examina-
tion the next morning at sunrise, the
thermometer lying on the unprotected
wool will be lower and that parcel will
also weigh more than the other. Whyf
One explanation covers both facts. The
unprotected wool radiated, without oh.
strnction, its heatinto free space. Hence
Its temperature was more reduced and
the deposit of dew, increasing its weight,
was accordingly greater. Hence the
practice of gardeners in stretching loose
mating, or even extending board,
over tend z vegetation when frost
is feared. Like the clouds, the con-
trivances reflect back the ridiant heat,
aud less reduction of temperature is the
result. -
(3) For the deposit fdew to be copious
the atmosphere must be still. Why?
Consider a meadow thickly set in
grass. The grass is radiating its
heat, as. rapidly becoming chilled.
If the atmosphere be still, it
will also become chilled by contact with
the cold grass, and its vapor will be con-
densed aud deposited. But when the at
mosphere is in motion, the same stratum
of air does not brood over the cold grass
long enough to have its temperature
sufficiently reduced to condense its yopor.
1t is for these reasons, that the farmer,
particularly the tobacco grower, when
threatened by frost-which is but frozen
dew.-fears the still, clear night. At the
close of an anxious day, his fears
vanish if clouds appear, or. thel. wind
rises. We summarize these points
by sayi,, :, that for cepious deposits of
dew, the atmosphere must be humid,
still and serene.
(4) There is another matter connected
with the formation of dew, which is we'll
calculated to arrest attention. All OBJ.
iects possess different radiating powers,
and hence lose heat at night with differ
eut rates Of facility. Living vegetation
radiates heat far more freely than dead
vegetation or any form of organic matter.
Consequently when the supply of dew is
sparse, living vegetation, which needs it
gets all or nearly all; dead matter gets
none or nearly none. Hence at all is
discoverable on the gravel walks, on the
plank fences, or ricks of straw Nature,
though prodigal of her gifts, is not the
less frugal. When the supply of dew is
moderate, she bestows it exclusively on
objects that need its life.giving power, and
gives it to the objects that need it less
only when the supply is large and she
can afford to be lavish. What wonder.
full wisdom is that which has endowed
the different forms of matter with the
power Of wringing water from the invist-
BILE atmosphere in exact proportion to Their
several wants? Can it be other than
divine? Somebody else, besides the
undevout astronomer, is mad.
According to the foregoing, plants
must be chilled in order to obtain the de-
posit of dew. When the cold is sufficient
to freeze the dew, then we have frost and
the consequent cessation of vegetable life.
The plant, then, must be chilled to OBJ
tain the dew it needs, and yet is liable to
be killed by the very cause that is neces
sary to the deposit. To ward off this
danger and to protract and invigorate veg
etable life, another beautiful and striking
provision comes into play. Let us see.
I'VE heat volume of water at such rate
that its Temperature rises, say, 10 degrees
Der minute. When the temperature
reaches 2l2 degrees, the thermometer
placed in the water ceases to rise, but
becomes stationary and remains so for
100 minutes, at the end of which time all
the water is gone,-is converted into
steam. During this 100 minutes, the
source of heat being constant, 10 degrees
entered every minute, aud yet the water
and escaping steam stood at 2l2. What
has become of this 1000 degrees of heat,
which has not made the water or the
steam hotter, of which the thermometer
takes no cognizance? 1t has been en-
ployed in efecting a change of state,
converting liquid water into the vapor OF
water. Urge on the heat as We will after
water begins to boil, it gets no hotter.
The water is 2l2, the escaping steam il
2l2. All this excess of heat is spent in
convertinga liquid iuto its vapor, aud is
called latent heat, because neither our
feelings nor the thermometer can detect
it. Now, when the vapor OF water,
becomes water, this latent heat Is thrown
out and causes an elevation of oftemperature.
Nature performs for US on grand scale
experiments illustrative Of this principle.
When clouds begin to form, that is when
voycr sordeuws into wsseri tee1s u sts