*2Q£ SEICHE!, OF THE LAKE OF GENEVA. 



.WC may compare a lake of this form to a fyphon full of water, 

 >of which the branches fliould very much differ in diameter; 

 and it will be evident that if, for example, their inequality 

 being as fourteen to one, the fmalleft branch fliould fuddenly 

 receive by the augmentation of the almofphere a furcharge 

 equal to that which dep relies the barometer one line, it would 

 fall 11 lines, and the water which would be driven into the great 

 branch would raife ,its furfaee only one line; whereas, on the 

 contrary, a furcharge which fliould deprefs the level of the 

 great branch only one line, would raife it for a moment four- 

 teen in the fmaller. The effect would be double if at. the fame 

 time the weight of the atmofphere fliould diminish on one of 

 the branches, and encreafe on one of the other. We may 

 therefore admit that in lakes, the breach:, of which is remark- 

 ably contracted in fome part, the influer.'v »f the variations of 

 the atmofphere to produce feiches will be greater in the narrow 

 than in the wide part. 

 And alfo by cir- A like effect will take place according to Mr. Vaucher, by 

 cumftances at- rea fon of the inclination obfervable in that part of the. furfaee 



tending the _* ; , : ' . 



fl>wingoff of °* t,ie m^g near the place where.it ducnarges its water. He 

 the waters. remarks that every particle of a liquid on a flope may be con- 

 sidered as folicited by two forces; one which tends to raife it 

 to the level of the iuperior part of the dope or the refervoir, 

 and the other which urges it in the direction of the current. 

 If by the fudden depreffion of the fuperior fluid the current 

 be for a moment fuppreffed, the particle will no longer find 

 jlfelf urged but by the firft of thefe forces, and will rife to- 

 wards its ancient level, and foon afterwards defcend. Now, 

 as we have before feen, all the parts of lakes which have very 

 perceptible feiches have a remarkable fiope; this dope is natu- 

 rally more coniiderable at thole times of the year when the 

 waters are higheft, and thefe are the periods when the feiches 

 are. mod (hiking in the neighbourhood of Geneva, i 

 Singular appear- Independent of the phenomenon of the feiches, the lake of 

 ance which £,eneva and mod other lakes afford two other lingular pheno- 



[hTt e the e LTface SiTlena i the one is knqv ™ b > tb<J ^^en of the JLeman lake 

 of the lake is lpy the name of fontaines. This takes place when the furfaee 



partly (Vnooth Q jr iC Q ] u j ce inftead of being uniformly calm or uniformly agi- 

 and partly agi- . rt , i • • 



kited, tated, is teen to have certain parts calm and certain parts agi- 



tated, which are often mixed among each other in a thoufand 

 manners, and always very diftinch This fact feeuis to indi* 



ca^e 



