Abstract
THE so-called seiches, or alternate flux and reflux of water in the Lake of Geneva and other bodies of fresh water, have, as our readers know, formed the subject of an interesting study during the past decade by Dr. F. A. Forel, of Morges, near Geneva. Small local tides are constantly noticeable there, the difference between ebb and flow varying from a few centimetres to 2 metres. Their cause is to be traced to the wind, variations in atmospheric pressure at the extremities of the lake, &c. Dr. Forel, as the result of his investigations has established a formula by means of which the duration of a local ebb and flow can be determined—not only for the Lake of Geneva, but for any lake—when its average depth and its length are known. The following is the formula T=2(2 L)/(√g h) in which L denotes the length of the lake, h its average depth, and g the acceleration of gravity. This formula gives for the Lake of Geneva, which has a length of moon. M. Forel, in his explanation, shows that the regular ebb and flow twice a day in the former period is due to the tidal movement of the Ægean Sea, which is then at its maximum. The increase in the number of tides daily becomes manifest, however, when the tidal force of the Ægean is at its minimum, viz., at the quadratures, and must be owing to some other force more powerful than the minimum but less powerful than the maximum force of the Ægean tide. This force is found in the local tides or seiches of the Gulf of Talanti to the north of the straits, which is so shut in by land that it can practically be regarded as subject to the same laws as the lakes of Switzerland and other countries. This basin is 115 kilometres long, and is from 100 to 200 metres in depth. Applying these figures to M. Forel's formula, the ebb and flow in the Gulf of Talanti would be for 100 metres, 122 minutes; for 150 metres, 100 minutes; for 200 metres, 86 minutes. The eleven to fourteen currents observable daily at Euripus during the quadratures last from 103 to 131 minutes. This shows so striking a conformity with the theory advanced by the Swiss savant, that we can but consider this problem, which so vexed the ancients, as fairly solved.
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A Tidal Problem . Nature 21, 186 (1879). https://doi.org/10.1038/021186a0
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DOI: https://doi.org/10.1038/021186a0