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. Sir Robert Sibbald describes a very remarkable marine whirlpool among the Orkney islands, which would prove dangerous to strangers, though it is of no consequence to the people who are used to it. It is not fixed to any particular place, but arises in various parts of the limits of the sea among these islands. Wherever it appears, it is very furious, and boats would inevitably be drawn in and perish with it, but the people who navigate them are prepared for it and always carry a bundle of straw or some such matter in the boat with them. This they fling into the vortex which immediately swallows it up, and, seemingly pleased with this propitiatory offering, subsides into smoothness, but soon after re-appears in another place. A remarkable and sudden rising of the spring-tide takes place at the mouth of several rivers, for instance, the Indus (where the surprising phenomenon nearly caused the destruction of the fleet of Alexander the Great), the Hooghly, the Dordogne, &c. In the Seine it is observed on a scale of great magnitude. While the tide gradually rises near Havre and Harfleur, a giant wave is suddenly seen to surge near Quillebœuf, spanning the whole width of the river (from 30,000 to 36,000 feet). After this mighty billow has struck against the quay of Quillebœuf, it enters a more narrow bed and flows stream-upwards with the rapidity of a race horse, overflowing the banks on both sides, and not seldom causing considerable loss of property by its unexpected appearance. The astonishment it causes is increased when it takes place during serene weather, and without any signs of wind or storm. A deafening noise announces and accompanies this sudden swelling of the waters, which owes its first origin to the silent action of gravitation, and is the result of the diminishing velocity of the tide-wave over a shallow bottom. While the tide-wave advances over the deep and open seas with an astonishing rapidity, its progress up the channel of a river is comparatively very slow, partly on account of the reason just mentioned, and partly from its meeting a current flowing in an opposite direction.