In a case of actual circulation due to difference of gravity, there is always a constant disturbance of both _static_ and molecular equilibrium. Column C is always higher and column W always lower than it ought to be were the two in equilibrium; but they never can be at the same level. It is quite conceivable, of course, that the two conditions of equilibrium may be fulfilled alternately. We can conceive column C remaining stationary till the water flowing from column W has restored the level. And after the level is restored we can conceive the polar column C sinking and the equatorial column W rising till the two perfectly balance each other. Such a mode of circulation, consisting of an alternate surface-flow and vertical descent and ascent of the columns, though conceivable, is in reality impossible in nature; for there are no means by which the polar column C could be supported from sinking till the level had been restored. But Dr. Carpenter does not assume that the general oceanic circulation takes place in this intermitting manner; according to him, the circulation is _constant_. He asserts that there is a “_continual_ transference of water from the bottom of C to the bottom of W, and from the top of W to the top of C, with a _constant_ descending movement in C and a _constant_ ascending movement in W” (§ 29). But such a condition of things is irreconcilable with the idea of “the levels of the two columns, and consequently their heights, being maintained at a _constant_ equality” (§ 29). Although Dr. Carpenter does not admit the existence of a permanent difference of level between the equator and the pole, he nevertheless speaks of a depression of level in the polar basin resulting from the contraction by cooling of the water flowing into it. This reduction of level induces an inflow of water from the surrounding area; “and since what is drawn away,” to quote his own words, “is supplied from a yet greater distance, the continued cooling of the surface-stratum in the polar basin will cause a ‘set’ of waters towards it, to be propagated backwards through the whole intervening ocean in communication with it until it reaches the tropical area.” The slope produced between the polar basin and the surrounding area, if sufficiently great, will enable the water in the surrounding area to flow polewards; but unless this slope extend to the equator, it will not enable the tropical waters also to flow polewards. One of two things necessarily follows: either the slope extends from the equator to the pole, or water can flow from the equator to the pole without a slope. If Dr. Carpenter maintains the former, he contradicts himself; and if he adopts the latter, he contradicts an obvious principle of mechanics.