296 Oil the Seiches of the Lake q/' Geneva* 



versal mist, or when rain or snow were falling widely ; whilst, 

 on the contrary, the seiche was always considerable when the at- 

 mosphere was studded with formidable clouds, or when the 

 weather, otherwise serene, just preceded a storm, and when the 

 barometer was falling. 



Asth, That, all other things being equal, the seiches are more 

 considerable in the Lake of Geneva in proportion as we approach 

 its dehouchement into the Rhone ; that they are most of all consi- 

 derable at this part, and from this spot decrease to the confluence 

 of the Rhone with the Arve, where they nearly wholly disappear. 

 That the same is true in proceeding towards the other extre- 

 mity of the lake, as far as Coppet, where they occur to the ex- 

 tent of only an inch or two, and as far even as Rolle, where they 

 are still less, but yet nowhere they do entirely disappear. 



5thy That the eastern extremity of the Lake of Geneva does 

 not exhibit seiches more remarkable than other lakes, though the 

 opposite opinion seems established in the works of Saussure. 



Qth, That although the seiches are more frequent in spring 

 and autumn than at other seasons, yet they are to a greater ex- 

 tent in summer, and especially towards the end of that season. 

 The largest that have been ever observed have always occurred 

 in the months of July and August, or at the beginning of Sep- 

 tember. 



T^A, That the minimum of seiches has no limit, but that their 

 maximum never exceeds five feet. Amongst the most consider- 

 able are the four particularized by Fatio de Duilliers in his 

 Mk-nwire sur VHistoire Naturelle de Geneve, inserted at the end 

 of Spon's History of Geneva, and those which Messrs Serre and 

 De Saussure observed together on the 3d of August 1763. 



Hth, Finally, that the duration of the seiche is very variable, 

 its higher limit seldom exceeding twenty or twenty-five minutes, 

 usually much less, whilst its lower is nothing. 



And now to explain these different particular circumstances of 

 the phenomenon : — 



1*^, There must be a cause whioh is capable of disturbing the 

 level of the surface of lakes which may act at all times, and with 

 different degrees of intensity, whose influence increases with 

 atmospherical variations, and especially at the approach of 

 storms. 



