302 On the Seklies of' tlie Lake of Geneva. 



many of the Swiss lakes, and more remarkably that of Geneva. 

 But it still remains to explain how this cause should f)roduce 

 at the western extremity of the lake just named, effects which 

 are so much greater in their extent than those which are ob- 

 served in the others ; and it is of this fact, that M. Vaucher en- 

 deavours to give an explanation in the last part of his memoirs. 



M. Vaucher remarks, that if we cast our eyes upon the map 

 of Switzerland, we shall find that, with the exception of the 

 Lake of Constance, the Lake of Geneva is that in which the nar- 

 rowing is most considerable at its extremity. Its width at 

 Thun is nearly eight times as much as it is at Eaux-Vives, 

 and it insensibly gets narrower all the way from Nyon to Gene- 

 va. Independent of this narrowing, it presents another phe- 

 nomenon which, according to the author, does not occur in any 

 of the others, at least to the same extent ; it is, that those wa- 

 ters at the place where they begin to acquire the movement by 

 whicli they escape, have already a sensible declivity, and this 

 at about the distance of three miles: According to some ob- 

 servations which are contained in the memoir already quoted of 

 M. Fatio de Duillier, and after a new measurement of the 

 levels executed by himself, M. Vaucher concludes, that the de- 

 clivity of the lake from Genthod to Geneva, being three miles of 

 distance, is when the waters are low about a foot ; that it is 

 more than double of this in the month of June ; and that it 

 attains its maximum in the month of August, when it may 

 extend to about four feet, when at its usual high level, or at all 

 events, on extraordinary occasions. 



Moreover, continues M. Vaucher, so great a declivity is not to 

 be found in any other lake with which I am acquainted ; that of 

 Annecy has not even a sensible current where the river runs out 

 from it ; that of Zurich is under the same circumstances, and 

 that of Geneva itself, at its other extremity, has scarcely any 

 declivity ; for the Rhone, at its entrance, does not, on its cur- 

 rent, carry the boats farther than three hundred yards. The 

 only lake which seems to be an exception is that of Constance, 

 concerning which M. Macuaire informed me that the declivity 

 is apparent, and that it commenced about two-thirds of a mile 

 above the town of the same name. But this fall, which has 

 never, I believe, been n>easured, and which I have witnessed 



