because it receives more heat from the sun than column C. Consequently Dr. Carpenter’s statement that the circulation is produced by polar cold rather than by equatorial heat, is just as much in contradiction to his own theory as it is to the principles of mechanics. Again, his admission that the general oceanic circulation “cannot be produced by the application of heat to the surface,” is virtually a giving up the whole point in debate; for according to his gravitation theory, and every form of that theory, the circulation results from _difference_ of temperature between equatorial and polar seas; but this difference, as we have seen, is entirely owing to the difference in the amount of heat received from the sun at these two places. The heat received, however, is “surface-heat;” for it is at the surface that the ocean receives all its heat from the sun; and consequently if surface-heat cannot produce the effect required, nothing else can. _M. Dubuat’s Experiments._—Referring to the experiments of M. Dubuat adduced by me to show that water would not run down a slope of 1 in 1,820,000,[82] he says, “Now the experiments of M. Dubuat had reference, not to the slow restoration of level produced by the motion of water on itself, but to the sensible movement of water flowing over solid surfaces and retarded by its friction against them” (§ 22). Dr. Carpenter’s meaning, I presume, is that if the incline consist of any solid substance, water will not flow down it; but if it be made of _water_ itself, _water_ will flow down it. But in M. Dubuat’s experiments it was only the molecules in actual _contact_ with the solid incline that could possibly be retarded by friction against it. The molecules not in contact with the solid incline evidently rested upon an _incline of water_, and were at perfect liberty to roll down that incline if they chose; but they did not do so; and consequently M. Dubuat’s experiment proved that water will not flow over itself on an incline of 1 in 1,000,000. _A Begging of the Question at Issue._—“It is to be remembered,” says Dr. Carpenter, “that, however small the original amount of movement may be, a _momentum_ tending to its continuance _must_ be generated from the instant of its commencement; so that if the initiating force be in constant action, there will be a _progressive acceleration_ of its rate, until the increase of resistance equalises the tendency to further acceleration. Now, if it be admitted that the propagation of the disturbance of equilibrium from one column to another is simply _retarded_, _not_ prevented, by the viscosity of the liquid, I cannot see how the conclusion can be resisted, that the constantly maintained difference of gravity between the polar and equatorial columns really acts as a _vis viva_ in maintaining a circulation between them” (§ 35).