THE LAKE Ol" CONSTANZ, ETC.

333

ßut though smaller in superficial extent than tlie Lake otGeneva, it exceeds it in the volume of its water, being upwardsof 300 yards in deptli at its most profound point; tlie Ueber-lingen Prolongation, however, lias adepth of but 500 feet, whilethe brauch called the Unter- (or Zeller-) See, measures only60 feet of water at its deepest part, and is fordable at others.

The elevation of the lake is between 1200 and 1300 feetabove the level of the sea, and yet it seldom freezes: it has,indeed, being covered with ice but five times in the last sixcenturies; viz. in the years 1277, 1560, 1573, 1695, and1829-30.

Sometimes, when the snow is melting rapidly in the Sum-mer—and from other causes not yet explained—the watersof the lake rise several feet (upwards of six or eight) in aday. The liquid Contents, however, are, as a rule, the smallestin the winter time, and the greatest in summer. (See foot-note, p. 312.) Numerous small streams augment the bodyof water poured in by the Rinne, and contribute, in a measure,to fill up tlie basin of the Lake.

The wind which is the most dangerous to boats upon theLake is that which comes from the south, and is called bythe Swiss, "Föhn." The danger arises not only from thesuddenness with which it bursts over the water, but to the" ground swell," which at such times is considerably increased.This ground-swell is termed " Ruhos" and is a phenomenonpeculiar to the Lakes of Constanz and Geneva: it consists ina sudden rising or commotion of the water—occasionallywithout any wind to stir it—which at such times is thrownup against the banks with considerable force. Tlie approachof the rahos is always indicated by a whitish-grey fog, fol-lowed by thick black clouds.

The lake abounds in fish, of which 25 specics have beenenumerated, and these are usually caught with nets.