Setting aside the wider question of the possibility of a general oceanic circulation arising from heat, cold, and evaporation, I believe that Captain Maury and Dr. Carpenter are the only authorities who of late years have disputed this source of the current which we see and can gauge and measure as it passes out of the Strait of Florida; for it is scarcely necessary to refer to the earlier speculations that it is caused by the Mississippi River, or that it flows downward by gravitation from a “head” of water produced by the trade-winds in the Caribbean Sea. Captain Maury writes that “the dynamical force that calls forth the Gulf Stream is to be found in the difference as to specific gravity of intertropical and polar waters.” “The dynamical forces which are expressed by the Gulf Stream may with as much propriety be said to reside in those northern waters as in the West India seas: for on one side we have the Caribbean Sea and Gulf of Mexico with their waters of brine; on the other the great polar basin, the Baltic and the North Sea, the two latter with waters which are little more than brackish. In one set of these sea-basins the water is heavy; in the other it is light. Between them the ocean intervenes; but water is bound to seek and to maintain its level; and here, therefore, we unmask one of those agents concerned in causing the Gulf Stream. What is the power of this agent? Is it greater than that of other agents? and how much? We can not say how much; we only know it is one of the chief agents concerned. Moreover, speculate as we may as to all the agencies concerned in collecting these waters, that have supplied the trade-winds with vapor, into the Caribbean Sea, and then in driving them across the Atlantic, we are forced to conclude that the salt which the trade-wind vapor leaves behind it in the tropics has to be conveyed away from the trade-wind region, to be mixed up again in due proportion with the other water of the sea--the Baltic Sea and the Arctic Ocean included--and that these are some of the waters, at least, which we see running off through the Gulf Stream. To convey them away is doubtless one of the offices which in the economy of the ocean has been assigned to it.” Dr. Carpenter attributes all the great movements of ocean water to a general convective circulation, and of this general circulation he regards the Gulf Stream as a peculiarly modified case. Dr. Carpenter states that “the Gulf Stream constitutes a peculiar case, modified by local conditions,” of “a great general movement of equatorial water toward the polar area.” I confess I feel myself compelled to take a totally different view. It seems to me that the Gulf Stream is the one natural physical phenomenon on the surface of the earth whose origin and principal cause, the drift of the trade-winds, can be most clearly and easily traced.