Thus it is in the Southern Ocean, where the greatest uninterrupted surface of deep water is exposed to the influence of the moon, that we must look for the "chief cradle of the tides." From this starting point they flow on all sides to the northward, progressing like any other wave that arises on a small scale in a pond from a gust of wind, the throwing of a stone, or any other cause capable of producing an undulating movement on the surface of the waters.
The tide-wave, which ultimately reaches our shores, arrives at the Cape of Good Hope thirteen hours after it has left Van Diemen's Land, and thence rolls onward in fourteen or fifteen hours to the coasts of Spain, France, and Ireland. It penetrates into the North Sea by two different ways. One of its ramifications turns round Scotland and thence flows onwards to the south, taking nineteen or twenty hours for the passage from Galway to the mouth of the Thames. A tide-wave, for instance, which appears at five in the afternoon on the west coast of Ireland, arrives at eight near the Shetland Islands, reaches Aberdeen at midnight, Hull at five in the morning, and Margate at noon.
The other ramification of the same tide-wave, taking the shorter route through the Channel, had meanwhile preceded it by twelve hours, having reached Brest about five o'clock of the afternoon (at the same time that the northern branch appeared at Galway), Cherbourg at seven, Brighton at nine, Calais at eleven, and the mouth of the Thames at midnight.
Thus, in this southern corner of the North Sea, two tide-waves unite that belong to two successive floods; the Scotch branch having started twelve hours sooner from the great Southern Ocean than the Channel branch, which thus results from the next following tide. The meeting of the two branches naturally gives rise to a more considerable rising of the waters, so that this circumstance, by allowing large ships to sail up the Thames, may be considered as one of the fundamental causes of the grandeur of London.
In other parts of the North Sea, where the two tide-waves appear at different times, the contrary takes place, for the ebb of the one coinciding with the rising of the other, they naturally weaken or even neutralise each other. This occasions the low tides on the coast of Jutland, in Denmark, where they are scarcely higher than in the Mediterranean, and explains the otherwise startling fact of there being a space in the North Sea where no periodical rise and fall of the waters whatsoever takes place.
Thus we see that the relations of the tides in the North Sea, with regard to height and time, are of a somewhat complicated nature, which could only be explained after the numerous observations (amounting to more than 40,000) made by order of the British Government in all parts of the world, under the direction of Professor Whewell, had proved that all the floods of the seas chiefly proceed from the great tide-wave of the Southern Ocean, which, by its numerous ramifications in narrow seas or through groups of islands and by the unequal rapidity of its progress, according to the depth or shallowness of the waters it traverses, occasions all the seeming anomalies which were quite inexplicable by the simple Newtonian theory.
As every twelve hours a new tidal-wave originates in the Southern Ocean which regularly follows in the same track as its predecessor, the tides everywhere succeed each other in regular and equal periods, and can thus everywhere be calculated beforehand.
In narrow straits or in the intricate channels which wind through clusters of islands, different tidal-waves meeting from opposite directions give rise to more or less dangerous whirlpools. One of the most famous of these vortices, though inconsiderable in itself, is the renowned Charybdis, which gave so much trouble to Ulysses on his passing through the strait which separates Sicily from Italy, but is at present an object of fear scarcely even to the poor fisherman's boat.
A much grander whirlpool, owing its celebrity, not to the fictions of poetry, but to the magnificent scale on which it has been constructed by nature, is the renowned Maelstrom, situated on the Norwegian coast in 68° N. lat., and near the island of Moskoe, from whence it also takes the name of Moskoestrom. It is four geographical miles in diameter, and in tempestuous weather its roar, like that of Niagara, is said to be heard several miles off. John Ramus gives us a terrible description of its fury, and mentions that in the year 1645 it raged with such noise and impetuosity, that on the island of Moskoe, the very stones of the houses fell to the ground. He tells us also that whales frequently come too near the stream, and, notwithstanding their giant strength, are overpowered by its violence, but, unfortunately adds, that it is impossible to describe their howlings and bellowings in their fruitless struggles to disengage themselves—impossible, no doubt, as whales happen to have no voice at all!
According to more modern travellers, such as the celebrated geologist Leopold von Buch, the Maelstrom is far from being so terrible as depicted by Ramus and other friends of the marvellous; so that, except during storms and spring-tides, large ships may constantly cross it without danger. The Norwegian fishermen are even said frequently to assemble on the field of the Maelstrom on account of the great abundance of fishes congregating in those troubled waters, and fearlessly to pursue their avocations, while the whirlpool moves their boats in a circular direction.