On the Seiches of the Lake of Geneva. 301 



of a storm ; in explaining by their means the phenomena of 

 seiches, we must consider the waters of lakes as forming a syphon 

 with an infinite number of branches, some one of which com- 

 municates with all the others. We must also suppose that this 

 central branch, communicating with all the others, shall be for the 

 moment charged with a column of air, the weight of which va- 

 ries. If, then, this column experiences an augmentation of weight 

 or of tension, which corresponds to a line of mercury, and con- 

 sequently to fourteen lines of water, the subjacent water will have 

 a tendency to fall fourteen lines ; and this quantity which it will 

 fall in the central branch of the syphon, will be the measure of 

 the extent it will rise in the other branches which have not been 

 subjected to any change of pressure, that so the equilibrium may 

 be maintained. 



If, at the same time that there is an augmentation of pres- 

 sure on one column, there is also a diminution of pressure 

 on other columns, so that the mercury falls in one place, whilst 

 it rises in another, it is clear that in all these cases, and in 

 others of the same kind which may easily be imagined, the ef- 

 fects would be compounded and increased ; whilst at the same 

 time they would be dimthished or even destroyed when the 

 neighbouring columns are also augmented in weight, a circum- 

 stance which occurs whenever, in the middle of a regular ascen- 

 sion, the water becomes stationary or even descends. 



These barometrical variations are sufficient to account for the 

 differences which are observed in the level of the most part of 

 lakes. True it is, it is usually imagined that these lakes do 

 not present the appearance ; and this arises from the circum- 

 stance, that in fact they are not very apparent. Thus it has 

 always been supposed, that the lakes of Zurich, Annecy, and 

 Neufchatel, and many others, never exhibited them ; but I have 

 shewn, that, with attentive observation, there might be detected 

 differences of the level of the surface, which, in ordinary cir- 

 cumstances, extended to two or three lines, and which, at the 

 approach of storms, might extend beyond an inch. 



Upon the whole, then, it is difficult not to agree with M. 

 Vaucher ; and to perceive, in the ordinary and continued varia- 

 tions of the atmospherical pressure, the cause of the oscillations, 

 not less continual, which affect, in different degrees, the waters of 



VOL. XVII. NO. XXXIV.— OCTOBER 1834. X 



