200 



SEICHES OF THE LAKE OF GENEVA. 



theyfecmtobe Jo. This? phenomenon takes place in all temperatures, but 

 weight of the at- m g enera ' > l refults from very extent! ve tables, that the feiches 

 mofphere, and are more frequent, and more extreme, the more variable the 

 foretelraia. ^ ate °^ ^e atm °fphere. Remarkable variations of the 

 barometer have been obferved to correfpond with confiderable 

 feiches, and it is an opinion generally received among the 

 filliermen, that the feiches are a fign of change of weather. 

 In particular, they have been obferved to be very ftrong when 

 the fun comes to thine very ftrongly on a fpot, a (hort time 

 before obfcured by a thick cloud. 

 Explanations by After this expofition of the phenomenon, fome notion may 

 various autiors. ^ f orme( j refpecling the value of the different explanations. 

 M. Fatio attributes the feiches to violent gulls of wind which 

 drive the waters into the narroweft part of the lake. Mr. 

 Jalabert attributes them to fome fudden encreafe of the Arve, 

 which falling into the Rhone at a (liort diflance from the lake, 

 and entering the river at a confiderable angle, may in facr, 

 fometimes ftop its courfe for a thort period, and in that manner 

 raife the waters of the part of the lake neareft Geneva ; latily, 

 Mr. Bertrand thinks this phenomenon to be occafioned by 

 electrical clouds which attract the waters of the lake, and 

 produce ofciliations more fenfible, the nearer its oppofite 

 banks may be to each other. Without dwelling on the in- 

 sufficiency of thefe three hypothefis to account for all the 

 different facls before mentioned ; Mr. Vaucher obferves, 

 that the true explanation ought to be two-fold ; namely, 

 general in order to fhew the caufe of thofe left confiderable 

 feiches which are obferved in all the lakes, and over the 

 whole of their fur face ; the other mull be local, and explain 

 why this phenomenon is much more fenfible at the weftern 

 extremity of the lake of Geneva, than in any other known 

 place. 

 Mr. Vaucher With refpecl to the firft, Mr. Vaucher afcribes it to the 



afcnbes them to frequent variations which are fenfible in the weight of dif- 

 preflure acting ferent columns of the atmofphere, and consequently in the 

 more ftrongly on pretfure it exerts on different points of the furface of lakes *. 

 rake P than°at the ^ e ma y eau ' v conce » ve » that if the weight ol the atmofpheric 

 place of rife. column be fpeedily diminifhed in a given part of a lake, with- 



* This caufe was hefore indicated concifely by De Sauffure. in 

 his firft vol. of Travels in the Alps. 



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