Rainfall and climate in India / by Sir Joseph Fayrer.

  • Joseph Fayrer
Date:
[1881]
Catalogue details

Licence: Public Domain Mark

Credit: Rainfall and climate in India / by Sir Joseph Fayrer. Source: Wellcome Collection.

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    //s 3 permeated by another and no less important one of watery vapour, always present, though in varying quantities, accord- ing to circumstances of temperature, time, and place, derived from the ocean, the seas, lakes, pools, rivers, streams,—from the surface of the earth itself, and from all living things animal or vegetable. It is constantly rising and permeat- ing the air up to the point where saturation is reached, or until it is condensed by cold, into the sensible form of dew, clouds or rain. On the varying conditions under which evaporation, on the one hand, and condensation on the other, take place, the rainfall depends. The ocean is the great source whence atmospheric moisture is derived; it is the great bourne to which it all returns. As the wise king said,—“ All the rivers run into the sea, yet the sea is not full; unto the place from whence the rivers come, thither they return again.” The atmosphere is the great sponge that soaks up and holds the watery vapour, which, when condensed, falls into the ocean, or on to the earth, to fill the rivers, to sink into the ground, whence it rises again in springs, collects in wells, lakes, and pools, or runs off in streams and rivers, diffusing itself everywhere, ministering to the wants of nature, and supporting life and organisation; finally, to return to the ocean, again to rise in vapour, and repeat the endless circula- tion, without which life would be extinct, and the earth reduced to the condition of the moon, or of some effete worn- out world. Water is always evaporating; expose a cup of it to the air and it will soon disappear,—all the sooner if the air be dry and warm. So will ice or snow, in regions where the cold may prevent it from melting, but not from evaporating; it is not lost, but assumes the impalpable form of vapour, and mingles with the air. This process is going on wherever there is water, but more especially from that part of the ocean which, lying near the equator, is subjected to the continued heat of the vertical solar rays. Here vaporisation is most active, and the warm air, saturated with moisture, rising in constant currents to higher regions, is replaced by colder and heavier currents rushing in from towards the poles; in turn to be heated, charged with moisture, ascend, and so keep up a constant circulation, making the equatorial rain-belt the great distillery of nature. The wind goeth towards the south, and turneth about unto the north; it whirleth about continually, and the wind re- turneth again according to its circuits.” These perennial northern and southern currents, or trade winds, getting their
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