SECTION 10.CAUSE OF TIDES.
The doctrine of the Earth’s rotundity being fallacious, all ideas of “centre of attraction of gravitation,” “mutual attraction of Earth and Moon,” &c., &c., must be given up; and the cause of tides in the ocean must be sought for in another direction. It is certain that there is a constant pressure of the atmosphere upon the surface of the Earth and ocean. This is proved by ordinary barometrical observations, many Pneumatic experiments, and by the fact that during the most fearful storms at sea the surface only is disturbed; at the depth of a hundred feet the water is always calm—except in the path of well-marked currents and local submarine phenomena. The following quotations gathered from casual reading fully corroborate this statement. “It is amazing how superficial is the most terrible tempest. Divers assure us that in the greatest storms calm water is found at the depth of 90 feet.”[21]
[21]Chambers’s Journal, No. 100, p. 379.
[21]Chambers’s Journal, No. 100, p. 379.
“This motion of the surface of the sea is not perceptible to a great depth. In the strongestgale it is supposed not to extend beyond 72 feet below the surface; and at the depth of 90 feet the sea is perfectly still.”[22]
[22]Penny Cyclopædia, Article Sea.
[22]Penny Cyclopædia, Article Sea.
“The people are under a great mistake who believe that the substance of the water moves to any considerable depth in a storm at sea. It is only the form or shadow which hurries along like a spirit, or like a thought over the countenance of the ‘great deep,’ at the rate of some forty miles an hour. Even when the ‘Flying Dutchman’ is abroad the great mass of water continues undisturbed and nearly motionless a few feet below the surface.”[23]
[23]London Saturday Journal, August 8, 1840, p. 71.
[23]London Saturday Journal, August 8, 1840, p. 71.
“The unabraded appearance of the shells brought up from great depths, and the almost total absence of the mixture of anydetritusfrom the sea, or foreign matter, suggest most forcibly the idea ofperfect reposeat the bottom of the deep sea.”[24]
[24]Physical Geography of the Sea, by Lieut. Maury, p. 265.
[24]Physical Geography of the Sea, by Lieut. Maury, p. 265.
Bearing this fact in mind, that there exists a continual pressure of the atmosphere upon the Earth, and associating it with the fact that the Earth is a vast plane “stretched out upon the waters,” and it will be seen that it must of necessity slightly fluctuate, or slowly rise and fall in the water. As by the action of theatmosphere the Earth is slowly depressed, the water moves towards the receding shores and produces the flood tide; and when by the reaction of the resisting oceanic medium the Earth gradually ascends the waters recede, and the ebb tide is produced. This is thegeneralcause of tides. Whatever peculiarities are observable they may be traced to the reaction of channels, bays, headlands, and other local causes.
If a raft, or a ship, or any other structure floating upon water be carefully observed, it will be seen to have a gentle fluctuating motion. However calm the water and the atmosphere may be, this gradual rising and falling of the floating mass is always more or less observable. If vessels of different sizes are floating near each other they will be seen to fluctuate with different velocities, the largest and heaviest will move the least rapidly. This motion will be observable whether the vessels be held by their anchors, or moored to buoys, or freely floating in still water. A large and heavily laden vessel will make several fluctuations in a minute of time; the Earth once only in about twelve hours, because it is proportionately larger.
To this simple condition of the Earth,—the action or pressure upon it of the atmosphere, and the reaction or resistance to it of the water, may be traced all the leading peculiarities of thetides. The simultaneous ebb and flow upon meridians 180° apart. The absence of high and low water in large inland seas and lakes; which being contained within and fluctuating with the Earth cannot therefore show a relative change in the altitude of the surface. The flux and reflux observed in several inland wells and basins though far from the sea, but being connected with it by subterranean passages, necessarily show a relative difference in the surface levels of the earth and water. And the regular ebb and flood of the water in the great Polar sea recently discovered by Dr. Kane, although it is separated from the great tidal current of the Atlantic Ocean by deep barriers of ice—as will be seen by the following quotation:—“Dr. Kane reported an open sea north of the parallel of 82°. To reach it his party crossed a barrier of ice 80 or 100 miles broad. Before gaining this open water he found the thermometer to show the extreme temperature of -60°. Passing this ice-bound region by travelling North, he stood on the shores of an iceless sea extending in an unbroken sheet of water as far as the eye could reach towards the pole. Its waves were dashing on the beach with the swell of a boundless ocean. The tides ebbed and flowed in it, and I apprehend that the tidal wave from the Atlantic can no more pass under this icy barrier to be propagatedin seas beyond than the vibrations of a musical string can pass with its notes a ‘fret’ upon which the musician has placed his finger. * * * These tides therefore must have been born in that cold sea, having their cradle about the North Pole; and we infer that most, if not all, the unexplored regions about the Pole are covered with deep water; for, were this unexpected area mostly land, or shallow water, it could not give birth to regular tides.”[25]
[25]Physical Geography of the Sea, by Lieut. Maury, p. 176.
[25]Physical Geography of the Sea, by Lieut. Maury, p. 176.
That the Earth has a vibratory or tremulous motion, such as must necessarily belong to a floating and fluctuating structure, is abundantly proved by the experience of astronomers and surveyors. If a delicate spirit-level be firmly placed upon a rock or upon the most solid foundation which it is possible to construct, the very curious phenomenon will be observed of constant change in the position of the air-bubble. However carefully the “level” may be adjusted, and the instrument protected from the atmosphere, the “bubble” will not maintain its position many seconds together. A somewhat similar influence has been noticed in astronomical observatories, where instruments of the best construction and placed in the most approved positions cannot always be relied upon without occasional re-adjustment.