949
90 14.810
100 19.790
It is of course well understood that the atmosphere as a whole is
never saturated with water vapor. Such saturation is at the best
only local, as, for instance, on the seashore during quiet days,
when the layer of air over the water may be fully saturated, or in a
field containing much water from which, on quiet warm days, enough
water may evaporate to saturate the layer of air immediately upon
the soil and around the plants. Whenever, in such cases, the air
begins to move and the wind blows, the saturated air is mixed with
the larger portion of unsaturated air, and evaporation is again
increased. Meanwhile, it must be borne in mind that into a layer of
saturated air resting upon a field of growing plants very little
water evaporates, and that the chief water-dissipating power of
winds lies in the removal of this saturated layer. Winds or air
movements of any kind, therefore, become enemies of the farmer who
depends upon a limited rainfall.
The amount of water actually found in a given volume of air at a
certain temperature, compared with the largest amount it can hold,
is called the relative humidity of the air.
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