The Professor begins by saying that many works on physics, directly or
by implication, assert that the soil, by a well-known physical law,
gains moisture from the air by night. One author says "Cultivated soils,
on the contrary (being loose and porous), very freely radiate by night
the heat which they absorb by day; in consequence of which they are much
cooled down and plentifully condense the vapor of air into dew." Not all
scientific works, however, make this incautious application of the fact
that dew results from the condensation of moisture of the air in contact
with cooler bodies. Farmers have quite universally accepted the view
quoted, and believe that soils gain moisture by night from the air. This
gain is considered of very great importance in periods of droughts, and
is used in arguments favoring certain methods of tillage.
Professor Stockbridge, in 1879, at the Massachusetts Agricultural
College, carried on very valuable and full experiments in test of this
general belief, and arrived at results contradictory of this belief. He
found, in a multitude of tests, that in every instance, save one, for
the months from May to November, that the surface soil from one to five
inches deep, was warmer than the air instead of cooler, as the law
requires for condensation of moisture from the air.
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