Page:Encyclopædia Britannica, Ninth Edition, v. 10.djvu/163

Rh  1em  GENEVA, (the Latin Laws Lcmanus or Lake Leman, also known in the Middle Ages as Lac Losaimete or Lake of Lausanne, and as Mer du RhOne or Sea of the Rhone), is the largest of the Swiss lakes, having an area of 578 sq. kil. or 223 sq. miles. Its general form is that of a crescent, the northern shore being almost the arc of a circle, with a radius of 21% miles. The eastern end of the crescent is broad and rounded, while the western tapers towards Geneva. Its maximum breadth, between Merges and Aiiiphion, is 8:1,» miles. It is divided into two portions, the Great and Little Lake, by the strait of Promonthoux, which is not much more than 2 miles across. The Great Lake is 39 miles long, with a mean breadth of 6 miles, and the Little or Western Lake is 11 miles long, with a mean breadth of rather more than 2 miles. The bottom of the larger basin forms a wide valley, which gradually deepens from 200 to 325 feet at the foot of the slopes to a maximum of 1095 feet, which it attains between Oncliy and Evian. The mean level of the surface of the lake is 1230 feet abOVe the level of the sea. According to the elaborate soundings made in 1873 by M. Gosset, engineer of the Federal Topographic Depart- ment, the bottom is remarkably free from inequalities, almost all traces of rocks, erratic blocks, or moraines, having been covered over by a regular bed of extremely ﬁne argillocalcareous mud, which can be moulded and baked like potter’s clay. Between the basin of the Great Lake and that of the Little Lake there runs a ridge or bar not very strongly marked, 200 feet from the surface. The maximum depth of the lesser basin is only 71 metres or 233 feet. The bottom is apparently level, but it presents numerous erratic blocks, and in one place rises to a con- siderable eminence, known to the Genevese ﬁshers as the Hauts Monts. The unusual bluencss of the waters of the Leman has long been remarked. According to M. Forel, the transparency is very much greater in winter than summer, the extreme limit of visibility of a white disk on an average for the seven winter months from October to April being 41 feet, and for the ﬁve summer months 21'6. This arises from the thermal stratiﬁcation of the water keeping in suspension a greater quantity of dust and organic particles during summer. It is generally in August that the level of the lake reaches its highest limit, between 4 and 5 feet on an average above its lowest- limit, which is usually reached in March. Besides this seasonal change, due to differences of inﬂux and removal of water, several disturbances of level of a less obvious kind have attracted the attention of the Swiss physicists. Most remarkable are the sole/res, or “ movements of steady uninodal oscillation,” in which the whole mass of water in the lake rhythmically swings from shore to shore. According to M. Forel, there are both longitudinal and transverse seiclies. Their effect is most distinctly seen at Geneva, where they sometimes raise the level of the water from 4 to 5 feet. They are not improbany due to several distinct causes, but the most efﬁcient would appear to be a difference of barometric pressure in different parts of the lake. In the eastern portion of the lake there is an irregular but violent current during spring and autumn, called Lardeyre or La Dicre, which is supposed to be due to subterranean afﬂuents. The principal winds are the Bise from the north-east, the stormy Bornand that rushes from the ravines of Savoy, and the dry south wind, known as the Séchard. Less use is made of the lake as a means of communication since the opening of the railway along the Swiss shore, but the lateen sails of the minor craft still brighten the landscape, and an excellent steam service is maintained by a company formed in 1873. The ﬁrst steamboat, the “ William Tell,” was introduced on the lake in 1823 ; and the ﬁrst saloon steamboat, the “Mont Blanc,” dates only from 1876.

The Lake of Geneva is not so rich in ﬁsh as many of the smaller lakes of Switzerland. Comparativer small success has attended the attempts of Professor Chavannes of Lausanne to introduce the salmon, which, like many other ﬁshes, ﬁnds the Pertc du Rhone a barrier between