S. Winds
Diagram to shew how two opposing currents intersect each other
Surface Plan to shew how two opposing currents meet each other
W. & A. K. Johnston, Edinbr. and London.
Fig. 2
Now these two great ocean-currents are so compelled to intersect each other for the simple reason that they cannot turn aside, the one to the left and the other to the right. When two broad streams like those in question are pressed up against each other, they succeed in mutually intersecting each other’s path by breaking up into bands or belts—the cold water being invaded and pierced as it were by long tongues of warm water, while at the same time the latter is similarly intersected by corresponding protrusions of cold water. The two streams become in a manner interlocked, and the one passes through the other very much as we pass the fingers of one hand between the fingers of the other. The diagram ([Plate II.], Fig. 2), representing the surface of the ocean at the place of meeting of two opposing currents, will show this better than description. At the surface the bands necessarily assume the tongue-shaped appearance represented in the diagram, but when they have succeeded in mutually passing down through the whole thickness of the opposing currents, they then unite and form two definite under currents, flowing in opposite directions. The polar bands, after penetrating the Gulf-stream, unite below to form a southward-flowing under current, and in the same way the Gulf-stream bands, uniting underneath the polar current, continue in their northerly course as a broad under current of warm water. That this is a correct representation of what actually occurs in nature becomes evident from an inspection of the current charts. Thus in the chart of the North Atlantic which accompanies Dr. Petermann’s Memoir on the Gulf-stream, we observe that south of Spitzbergen the polar current and the Gulf-stream are mutually interpenetrated—long tongues invading and dipping down underneath the Gulf-stream, while in like manner the polar current becomes similarly intersected by well-marked protrusions of warm water flowing from the south. (See [Plate II.], Fig. 3.)
No accurate observations, as far as I know, have been made regarding the amount of work performed by the wind in impelling the water forward; but when we consider the great retarding effect of objects on the earth’s surface, it is quite apparent that the amount of work performed on the surface of the ocean must be far greater than is generally supposed. For example, Mr. Buchan, Secretary to the Scottish Meteorological Society, has shown[97] that a fence made of slabs of wood three inches in width and three inches apart from each other is a protection even during high winds to objects on the lee side of it, and that a wire screen with meshes about an inch apart affords protection during a gale to flower-pots. The same writer was informed by Mr. Addie that such a screen put up at Rockville was torn to pieces by a storm of wind, the wire screen giving way much in the same way as sails during a hurricane at sea.
The “Challenger’s” Crucial Test of the Wind and Gravitation Theories of Oceanic Circulation.—It has been shown in former chapters that all the facts which have been adduced in support of the gravitation theory are equally well explained by the wind theory. We may now consider a class of facts which do not appear to harmonize with either theory. The recent investigations of the Challenger Expedition into the thermal state of the ocean reveal a condition of things which appears to me utterly irreconcilable with the gravitation theory.