Books > Earth & environment > Earth sciences > The hydrosphere
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Neolithic Dew Ponds And Cattle Ways (1905) (Paperback)
Loot Price: R563
Discovery Miles 5 630
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Neolithic Dew Ponds And Cattle Ways (1905) (Paperback)
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Loot Price R563
Discovery Miles 5 630
Expected to ship within 10 - 15 working days
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"There is in England] at least one wandering gang of men... who
will construct for the modern farmer a pond which, in any suitable
situation in a sufficiently dry soil, will always contains water.
The water is not derived from springs or rainfall, and is speedily
lost if even the smallest rivulet is allowed to flow into the pond.
"The gang of dew-pond makers commence operations by hollowing out
the earth for a space far in excess of the apparent requirements of
the proposed pond. They then thickly cover the whole of the hollow
with a coating of dry straw. The straw in turn is covered by a
layer of well-chosen, finely puddled clay, and the upper surface of
the clay is then closely strewn with stones. Care has to be taken
that the margin of the straw is effectively protected by clay. The
pond will eventually become filled with water, the more rapidly the
larger it is, even though no rain may fall. If such a structure is
situated on the summit of a down, during the warmth of a summer day
the earth will have stored a considerable amount of heat, while the
pond, protected from this heat by the non-conductivity of the
straw, is at the same time chilled by the process of evaporation
from the puddled clay. The consequence is that during the night the
warm air is condensed on the surface of the cold clay. As the
condensation during the night is in excess of the evaporation
during the day, the pond becomes, night by night, gradually filled.
Theoretically, we may observe that during the day, the air being
comparatively charged with moisture, evaporation is necessarily
less than the precipitation during the night. In practice it is
found that the pond will constantly yield a supply of the purest
water.
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