An account of a voyage to establish a colony at Port Philip in Bass's Strait on the south coast of New South Wales, in His Majesty's Ship Calcutta, in the years 1802-3-4/Addendum 1
|←Chapter 5||An account of a voyage to establish a colony at Port Philip in Bass's Strait on the south coast of New South Wales, in His Majesty's Ship Calcutta, in the years 1802-3-4 by
|Addendum 2 →|
THOUGH the currents of the ocean have long occupied the attention of scientific men, no general theory has yet been found to answer under all circumstances. It may, I think, be assumed that oceanic currents depend upon principles as fixed as those to which we refer the currents of air; and also, that heat and cold operate in like manner upon both; to these causes may be added the influence of the heavenly bodies, and it is therefore to be regretted, that navigators have never thought of comparing with accuracy the changes and courses of currents with the revolutions of the sun and planets. Colonel Capper observes, that "the currents in the northern Indian ocean, the gulf of Sind, and the bay of Bengal, almost invariably take the same course as the wind. The cause of this connection between the wind and water seems almost to speak for itself; from the vernal to the autumnal equinox, that is, during the S.W. monsoon, the lower current of air, and also the waters of the southern hemisphere are put in motion, to fill up a vacuity, caused by the rarefaction of the atmosphere, and the evaporation of the waters of the northern atmosphere, both of which are increased near the land. And on the contrary, from the autumnal to the vernal equinox, when the sun is on his return to the tropic of Capricorn, the atmosphere being over every part of the southern hemisphere, the wind and water operated on by the same causes, will move in a contrary direction from the N.E. to the S.W. As a confirmation of this hypothesis, currents ore always found in proportion to the strength of wind, and both the wind, and currents grow weaker towards each equinox." The currents running to the northward in the Indian ocean, between the vernal and autumnal equinoxes, may also be strengthened by the fusion of the southern polar ices, during the southern summer solstice; and this will operate, though in a diminishing ratio, until the sun reaches the equator on his return to the southern hemisphere. See St. Pierre's Theory of Currents in "Les Etudes de la Nature."