The Indianapolis journal. [volume] (Indianapolis [Ind.]) 1867-1904, 1884-11-05
THE FARM AND HOUSEHOLD.
THE FARM.
Dew and Frost.

Philadelphia Record.
Every farmer knows that dew is present be-
fore the sun rises, during certain seasons, even
in the dryest of periods, and the fact that frostis
but frozen dew is also familiar to all. For valu-
able information in regard to the formation of
dew, and its relation to plants, we are indebted
to Prof. Puryear, of Virginia, from whose arti
Gle in the American Farmer the following is
condensed: 1t is obvious that during the first
days and weeks of piant life dew is most needed,
because at that time the r~ootlets must get their
supply of moisture from near the surface, which
is liable to become dry. Nature, however, pro
vides for this. Objects to have dew deposited
upon them must become sufficiently chilled at
night, by the radiation of heat, to condense the
aqueous vapor of the atmosphere. All objects
must be reduced in temperature to the dew
point. This is much more easily accomplished
in May than in August, for two reasons. In
May the sun is not so hot, nor does it shine so
long, as in August. nor is the temperature of the
atmosphere and of the earth'S surface as ele-
waited in the day during May as in August. To
get dew, objects have to sink at night to the
dew point, to a much lower temperature in May
than in August, for in the latter month they
must sink from so to 80 degrees, and during the
former from 60 to 70 degrees, to get to the dew
point. In order, therefore, to get a copious de-
post of dew. plants have less work to do in
spring or fall than in summer, and they have
more time to do it in, and hence the abundant
deposit in the spring and fall and the scant sup
ply in midsummer.
Dew is less needed in summer than in spring
or fall, for the reason that as the season ad-
vances the roots are striking down deeper and
deeper every day. Rain may not fall for weeks,
yet the roots are getting moisture from below
all the while, but when plants have just com
pleted termination, and when their roots are
near the surface. a drought of a few days would
be fatal but for the nightly deposits of dew.
The benefits derived from the heavy dews in the
early fall are reaped by the young plants of
wheat. rye, turnips and the grasses.
No cot No 100, Af 1Ar 4ho I \ O ~ net
be chilled, but If chilled too much the dew is
frozen into frost and vegetable vitality de-
stroyed. To secure a benefit danger is incurred:
but in the very process of securing the benefit
the danger is weakened. Vapor is water with a
certain amount OF heat in it-heat in the latent
state. When we condense this vapor the heat,
before latent. is evolved or given out When
aqueous vapor is in the process of condensation
into dew all its latent heat 1.-THE heat that made
it vapor) is evolved on the surface where the
condensation takes place. Consider a fine
tobacco field, it's broad leaves ripening in the
mild September. The leaves lose heat rapidly
by radiation, they become chilled, and the
aqueous vapor is condensed into dew, but in
such act its latent heat is evolved and warns up
the leaves, thereby lessening the liability of
injury from frost. The atmosphere Immediately
hrooding over the leaves is sensibly warmer than
the atmosphere elsewhere. If the same amount
Of water be sprinkled at nightfall upon the
leaves the cold may be sufficient to freeze it,
but not sufficient if this water has condensed
from vapor, for the process of condensation
throws out, in sensible form, the latent heat of
the vapor.
The process of aqueous condensation, or dew
formation, postpones the appearance of frost,
Plants must become chilled to form dew, but in
such condensation heat is thrown out TO prevent
frost. This battle goes on for weeks, until at
last the increasing length and GOODNESS of the
nights get the advantage, for then the cold be-
comes too great to be eounterbalanced by the
heat evolved from aqueous condensation, the
dew freezes as it falls, and the plant is killed.
The effect of moisture through the agency Of
rains and dews is not always the same. In the
case of tobacco little rains and copious Jews in
the early fall make tobacco leaves thick, heavy
and oily, and its quality is improved by com
paratively dry weather and heavy Jews. Dews,
then, to some extent, furnish to all plants, in the
earliest stage Of their growth, small butfrequent
supplies of moisture, and enable some of them,
such as tobacco, to attain, while approaching
maturity, their highest perfection.