The Canton advocate. [volume] (Canton, D.T. [S.D.]) 1877-1897, 1879-07-10
9E A NEW THEORY OF DEW.

INVESTIGATIONS which Prof. Levi Stock
bridge has made at the Amherst agricultu
raj college upon the comparative tempera-
ture of soil and air, and the deposition of
dew upon the earth and plants, have led
him to conclusions very different from
those commonly received in regard to the
formation of dew. It is usually held that
dew is the moisture of the air condensed
through contact with objects of q lower
temperature, and that it does not form till
radiation has reduced the temperature of
the earth and other objects below that of
the atmosphere. The experiments referred
to seem to indicate that, as regards objects
in the immediate vicinity of the earth, at
least, the process is the converse of this,
viz, that dew is the result of condensation
by the air of warm vapor as it rises from
the soil. The course of the experiments
from which this novel scientific theory was
deduced is outlined below.
The basis of the theory is the discovery
that in Summer the average temperature
of the earth at night is greater than that of
the atmosphere. The temperature OF the
earth in an inclosed space on level with
the surrounding soil, and the temperature
of the air, were taken at the warmest time
of day and the coldest time of night for
several months, and the average tempera-
ture of the air for the season was found to
be ~. $40 degrees, and that of the soil 72.-
O61 degrees But the average of the air at
night was 40. 664 degrees, and that Of the
soil 56 $40 degrees, the earth thus averag-
ing at night over six degrees warmer than
the atmosphere. The temperature of the
soil and air at night was also taken at va
Nous points within ten miles of the college.
on all kinds of grass land and bare soil, and
in the forest, and the same facts were OBJ
tanned, the soil being at all times warmer
at night than the air.
These results led to experiments on dew
fall. Two boxes each of cubic foot ca.
| pacty were filled with soil without disturb
ing its strata, one receiving absorbent, re-
tentive loan, and the other peat. These
| boxes were placed in trench in an open
| field, level with the surrounding ground,
and exposed to the weather. Through the
month of June they were weighed night
and morning, and unless there was rain in
the night they uniformly weighed less In
the morning than at night, the loss being
from one to three ounces for the loan, and
and one to four ounces for the peat. This,
Prof Stockbridge thought indicated that
the soil at night gave forth water, and that
the moisture found on the surface of a
field in the morning came from deeper
soil rather than from the air. Other simi-
lar experiments followed. In one q cab
bage plant was enclosed in an air-tight tin
case. Where the stem of the plant pro-
truded through the top of the case, wax was
used to make it impossible for moisture to
escape except through the leaves. The can
was first kept within doors and weighed
night and morning, when it always showed
loss during the night of from .21 grams
to 1.7S grams. When left out doors at
night, with the can wrapped in cloths to
prevent moisture reaching it, the loss was
| from .55 grams to ABB grams, showing q
loss even when there was moisture or dew
on the leaves.
These experiments continued through the
season gave Prof. Stockbridge these proofs
of his proposition that the dew on the
ground in the Summer is the condensation
Of vapor that rises from the earth: 1. The
vapor of the soil is much warmer at night
than the air and would be condensed by it
Q. Vapor from the soil is soon diffused and
equalized in the whole atmosphere, but in
largest proportion when evaporation il
taking place near the surface OF the soil
and other things being equal, plants nearest
the earth have the most dew. 8. Dew un.
der hay cocks, boards and like objects Oh
the ground could receive it from no othel
source.