Chapters VI. and VII. have been devoted to an examination of this form of the gravitation theory.
The above remarks apply equally to Dr. Carpenter’s form of the theory; for according to a doctrine of General Oceanic Circulation resulting from difference of specific gravity between the water at the equator and at the poles, the equatorial water will be carried more to the cold than to the warm hemisphere. It is perfectly true that a belief in a general oceanic circulation may be held quite consistently with the theory of secular changes of climate, provided it be admitted that not this general circulation but ocean currents are the great agency employed in distributing heat over the globe. The advocates of the theory, however, admit no such thing, but regard ocean currents as of secondary importance. It may be stated that the existence of this general ocean circulation has never been detected by actual observation. It is simply assumed in order to account for certain facts, and it is asserted that such a circulation must take place as a physical necessity. I freely admit that were it not that the warm water of equatorial regions is being constantly carried off by means of ocean currents such as the Gulf-stream, it would accumulate till, in order to restoration of equilibrium, such a general movement as is supposed would be generated. But it will be shown that the warm water in equatorial regions is being drained off so rapidly by ocean currents that the actual density of an equatorial column differs so little from that of a polar column that the force of gravity resulting from that difference is so infinitesimal that it is doubtful whether it is sufficient to produce sensible motion. I have also shown in Chapter VIII. that all the facts which this theory is designed to explain are not only explained by the wind theory, but are deducible from it as necessary consequences. In Chapter XI. it is proved, by contrasting the quantity of heat conveyed by ocean currents from inter-tropical to temperate and polar regions with such an amount as could possibly be conveyed by means of a general oceanic circulation, that the latter sinks into insignificance before the former. In Chapters X. and XII. the various objections which have been advanced by Dr. Carpenter and Mr. Findlay are discussed at considerable length, and in Chapter IX. I have entered somewhat minutely into an examination of the mechanics of the gravitation theory. A statement of the wind theory is given in Chapter XIII.; and in Chapter XIV. is shown the relation of this theory to the theory of Secular changes of climate. This terminates the part of the inquiry relating to oceanic circulation.