Page:Encyclopædia Britannica, Ninth Edition, v. 24.djvu/577

WHIRLPOOL 541 a mile in diameter. The edge of the whirl was represented by a broad belt of gleaming spray ; but no particle of this slipped into the mouth of the terrific funnel, whose interior, as far as the eye could fathom it, was a smooth, shining, and jet-black wall of water, inclined to the horizon at an angle of some 45, speeding dizzily round and round with a swaying and sweltering motion, and sending forth to the winds an appalling voice, half shriek, half roar, such as not even the mighty cataract of Niagara ever lifts up in its agony to heaven." Nothing could escape the violence of such a vortex. Whales caught in it were swallowed down, and the largest ship was engulfed as easily as the smallest boat. After an hour or two the funnel slowly filled, and the fragments of the vessels which it had sucked down were thrown up, dashed to pieces against rocks at an un known depth. Bearing such a reputation, whirlpools were naturally avoided by the mariner ; and their Teal nature long remained unknown. It was supposed that every whirlpool formed round a central rock ; under it opened a great cavern or gulf, down which the waters rushed, and so the whirling was produced as in a basin emptying through a central hole. This notion was developed by Athanasius Kircher (1602-80). In his theory whirlpools marked the entrances to subterranean channels connecting different seas, and the phenomena of tides were produced by the alternate flow of water in opposite directions. Kircher gives a curious diagram of the Malstrom or "umbilicus maris," illustrating his sup position that the water, after pouring into the vast funnel, flowed along a channel under the Scandinavian peninsula and rose in the Gulf of Bothnia. When the level of this gulf had been raised to a sufficient height, he thought that the current was reversed, and, aided by a stream pouring through a subterranean tunnel from the White Sea, raised the tide on the coast of Norway. Carrying his theory a degree farther to account for the Gulf Stream and the Antarctic drift, Kircher, with great ingenuity, placed a grand vortex at the North pole, down which all the water of the ocean tumbled, and, passing through the earth s axis, emerged at the South pole, thus keeping up " a circu lation like that of the blood in the human body." The facts which gave rise to the wild theories of medieval geographers and the extravagant descriptions of early voyagers are impressive enough in themselves to rank amongst the grandest phenomena of nature. No one who has seen the tide-streams racing through the Pentland Firth at 12 miles an hour, now swirling along with a smooth dimpled surface, like molten glass, now meeting the counter- current and leaping high into the air in columns of water and spray, or who has heard the roar of Corrievreckan as the Atlantic tide rushes between Scarba and Jura against an easterly gale, will be disposed to deny the terrible danger to small open vessels or to wonder that horror strengthened imagination to the confusion and exaggeration of fact. The formation of whirlpools is a natural result of water flowing rapidly in an irregular channel (see HYDROME CHANICS, vol. xii. pp. 468, 510) ; it takes place in all rivers and in every tide-race of the sea, the depth, diameter, and velocity depending on accidental causes. The form of the surface of an ordinary whirlpool is given by Prof. J. Thomson : as that generated by the revolution of a curve whose formula is y = c 3 /.*: 2 , where y is the depth of any point on the curve below the general level remote from the whirl, x the distance of the point from the axis of revolution, and c a constant. Every point on the surface moves with the velocity a heavy body would attain in falling from the general level of the water surface to that point, and any point in the interior of the revolving mass has a velocity equal to that of the point on the surface immediately above 1 Brit. Assoc. Hep., 1852, Sections, p. 130. itself. Prof. Thomson applied his researches on the motion of whirlpools to the construction of a particularly effective form of turbine. 2 All the famous whirlpools are situated in channels essentially similar in configuration and in tidal phenomena : their vortices are produced at certain phases of the tide or with certain directions of the wind ; and they are all dangerous to navigation, but the danger is due to the cause which produces the whirlpools the tidal race not to the " roaring wells " themselves. Whirlpools in a tidal stream are not stationary, but travel along with the current, fill ing up and again forming in irregular succession. Small boats have repeatedly been drawn into these vortices in the northern fjords and capsized ; and trading steamers in passing through a tideway are violently deflected from their course. It is on record that a seventy-four gun ship has been whirled right round in the vortices of the Straits of Messina. The fishermen of the Norwegian fjords and of the northern island groups, Lofoten, Faroe, Shetland, and Orkney, still believe that, if they can throw a heavy or bulky object into a whirlpool, it will close up without harming their boats. Lithgow in his Travels, speaking of the Pentland Firth, says, " I denote this credibly, in a part of the north-west end of this gulf there is a certain place of sea where these distracted tides make their rencountering rendezvous, that whirleth ever about, cutting in the middle circle a sloping hole, with which, if either ship or boat shall happen to encroach, they must quickly either throw over something into it, as a barrel, a piece of timber, and such like, or that fatal euripus shall then suddenly become their swallowing sepulchre." This custom, it has been supposed, is sacrificial in its origin. Its continued prac tice, however, suggests what is probably the case, that the bulky object splashing into the whirl breaks the continuity of the surface and causes a collapse or filling-ivp. In windy weather, when there is a broken sea, vortices are not formed. The tidal stream passing through the irregular channels between islands gives rise to a complicated series of eddies and counter-currents, which, according to the British Admiralty s Sailing Directions, make navigation dangerous, except when guided by local knowledge and aided by fair wind and a favourable tide. The general effect appears to be that, as the tide rises, the strength of the stream increases ; and the counter-currents set up along the shore, as well as the overfalls produced by inequalities of the bottom, thoroughly mix the water to a depth of from 50 to 100 fathoms. This has been proved by observations of temperature amongst the tidal currents off the Mull of Cantyre, where at all times of the year there is no differ ence between the surface and bottom temperature. At high water a state of rest ensues ; and ebb tide usually reverses the order of phenomena, the main stream, counter-currents, and eddies running in the opposite direction, but with nearly equal strength, until low tide brings another pause. Charybdis, a whirlpool famous in classical literature, is situated in the Straits of Messina. The rise of tide at Messina does not ex ceed one foot, but the current may attain the velocity of nearly 6 miles an hour. Where the north-going flood tide meets the south- running counter-current, and where the southerly ebb meets its induced northerly stream, great eddies or garofola are formed, one of which is Charybdis. These depend very much CHI the wind for the intensity of their phenomena. In ancient maps of the united Aral-Caspian Sea two whirlpools are represented. Near the position laid down there are in the river Amu-Daria two whirlpools at the junction of several channels. These have been recently examined 3 and found to arise from the river flowing over two conical hollows in its bed, respectively 120 and 60 feet deep ; these do not appear to have been formed by running water, but closely resemble craters of mud volcanoes. The most violent tidal current is said to be that of Salten Fjord to the south of BodiJ on the north-west coast of Norway, - Brit 3 Wood it. Assoc. Rep., 1852, Report, p. 317. ood, in Journ. Roy. Geoyr. Soc. (1875),

xlv. p. 372.