The Indiana State sentinel. [volume] (Indianapolis) 1868-1895, 1884-11-12
OUR FARM COLUMN.
Dew and FrOst-FertiIizing Grass Lands
Farm Notes-HousehOld, Etc.
Dew and Frost.
/ Philadelphia Record

Dew and Frost.
Philadelphia Record.l
Every farmer knows that dew is present
before the sun rises during certain seasons,
sVen in the dryest Of periods, and the fact
that frost is but frozen dew is also familiar
20 all. For valuable information in regard
to the formation of dew and its relation to
plants we are indebted to Professor Puryear,
OF Virginia, from whose article in the
American Farmer the following is con-
densed: 1t is obvious that during the first
days and weeks OF plant life dew is most
needed, because at that time the rootlets
must get their supply OF moisture from
near the surface, which is liable to become
dry. Nature, however, provides for
this Objects to have dew deposited upon
them must become sufficiently chilled at
night by the radiation Of heat, to condense
the aqueous Yapor OF the atmosphere. Ali
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 80 long, as in August, nor
Is the temperature of the atmosphere and of
the earth's surface as elevated in the day
during May as in August. To get dew OBJ
iects have to sink at night to the dew point
10 8 mach lower temperature in May than in
August. for in the latter month they must
sink from eighty or ninety degrees, and dur
ing the former from sixty or seventy degrees,
10 get TO the dew point. In order, there
fore, to get copious deposit 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 supply in mid
summer.
Dew is less needed in summer than in
spriDg or fall, for the reason that as the sea-
son advances 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 completed termination, and
winch their roots are near the surface, a
drought of few days would be fatal bat for
the nightly deposits OF dew. The benefits
deIi Ved from the heavy dews in the early fall
are reaped by the young plants of wheat,
rye, tuTnips and the grasses.
To get copious deposits of dew the plants
must be chilled, but if chilled too much the
uewis frozen into frost and vegetable vital.
ity destroyed. To secure a benefit danger
Is il CURED; but in the very process OF secur-
ing the benefit the danger is weakened.
Nspor 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 con-
densation into dew all its latent heat
ltbe heat that made it vapor) is evolved on
the surface where the condensation takes
place. Consider a fine tobacco field, its
broad leaves ripeDing 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 in
Jury from frost The atmosphere Immediately
brooding over the leaves is sensibly warmer
than the atmosphere elsewhere. If the same
amount Of water is sprinkled at nightfall
npOn the leaves the cold may be sufficient to
freeze it, but not sufficient if this water has
been condensed from vapor, for the process
Of condensation throws out, in sensible form,
the latent heat OF the vapor.
The process OF aqueous condemnation, 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 increas-
ing length and coldneSs of the nights get the
advantage, for then the cold becomes too
great to be counter-balanced by the heat
evolved from aqueous condensation, the dew
freezes as 1t falls, and the plants is killed.
The affect of moisture through the agency OF
rains and dews is not always the same. In
the case of tobacco little rain and copious
dews in the early fall makes tobacco leaves
thick, heavy and oily, and its quality is i'm
proved by comparatively dry weather and
heavy dews. Dews then, to some extent
furnish to all plants, in the earliest stage o.
their growth, small but frequent supplies Of
moisture, and enable some of them, such as
fOharCn
thrifty their highest perfection.