all times of the day; but, in general, more frequently in spring and autumn.  As regards the cause of the phenomenon, Vaucher shows how rapid local alterations of atmospheric pressure would produce oscillations in the level of the lake, and compares them to the vibrations of a liquid in a recurved tube or siphon.  Finally, Arago maintained that Seiches may arise from various causes, and traced the analogy between them and certain remarkable oscillations of the sea, including those arising from earthquakes.

But physical science is indebted to Professor F.A.  Forel, of Lausanne, for the most complete and exhaustive investigation in relation to the phenomena of Seiches.  This accomplished physicist began his researches in 1869, and has continued them up to the present time.  He has been able to demonstrate that these rhythmical oscillations occur in nearly all the Swiss Lakes (he studied the phenomena in nine of them), and that they follow in all cases the same general laws.  Those of the Lake of Geneva have received the most elaborate and prolonged investigation.  In March, 1876, Forel established a self-registering tide-gauge (limni-metre enregistreur) on the northern shore of this lake, at Morges; and, with the cooeperation of P. Plantamour, another one was installed in June, 1877, at Secheron, near the city of Geneva, at the southern extremity.  Since these dates, these two instruments have, respectively, been registering oscillations of the level of the water of the Lake of Geneva; and they are so sensitive as to indicate the waves generated by a steamer navigating the lake at a distance of ten or fifteen kilometers.

From a most searching investigation of all the phenomena presented by the Seiches in the Swiss Lakes, Forel deduces the conclusion that they are really movements of steady uninodal oscillations (balanced undulations), in which the whole mass of water in the lake rhythmically swings from shore to shore.  And, moreover, he shows that the water oscillates according to the two principal dimensions of the lake; thus, giving rise to longitudinal Seiches and transverse Seiches.  They occur in series of tautochronous oscillations of decreasing amplitude; the first wave produced by the action of a given cause having a maximum amplitude.

Causes.  The disturbances of hydrostatic equilibrium which generate Seiches may be produced by a variety of causes.  Among these, the following may be cited:  (a) Sudden local variations of atmospheric pressure on different parts of the lake. (b) A descending wind, striking the surface of the lake over a limited area, (c) Thunder-storms, hail-storms, and water-spouts; and especially when the accompanying winds act vertically. (d) The fall of a large avalanche, or of a land-slide into the lake. (e) And lastly, earthquakes.

Observations show that the most frequent