Lakes 305 



Thus on the Lake of Geneva it is, for the complete seiche, 630 

 seconds at Merges, and 1783 seconds at Veytaux; on Lake 

 Neuchatel it is 2840 seconds at Yverdon, and 264 seconds 

 at Saint Aubin. 



The curves traced by the gauge at Geneva have been 

 subjected to a preliminary harmonic analysis by Professor 

 Soret, and he has decomposed them into two undulations, the 

 one with a period, from crest to crest, of 72 minutes, and the 

 other with a period of 35 minutes, or a. little less than half 

 the larger period. As the amplitudes of the composing curves 

 vary much, there is great variety in the resultant curves. 

 Besides these two principal components, there are others 

 which have not yet been investigated. 



With regard to the cause of the phenomenon, Dr Forel 

 attributes the ordinary seiches to local variations of atmo- 

 spheric pressure, giving an impulse the effect of which would 

 be apparent for a long time as a series of oscillations. The 

 greater seiches, such as those of 1-5 metres, he attributed to 

 iquake shocks; but, as a very sensible earthquake passed 

 over Switzerland quite recently without leaving the slightest 

 trace on the gauge, he has abandoned this explanation, and is 

 in< lined to attribute them to pulsation set agoing by violent 

 downward gusts of wind, especially at the upper end of the 

 lake. M. Plantamour, who has devoted much attention to 

 the same subject, assured the writer, in the summer of 1881, 

 tli.it he was completely at a loss for a satisfactory explanation 

 of them. 



bcfl have not been observed on the Scottish lakes. 



mh there is little doubt that they would be found if sought 

 re are, however, records of disturbances of some of 

 tin- lakes, especial! v in Perth-hire, of \\hieh the following may 

 be cited as an instance. 



A violent disturbance of the level of Loch Tay is reported 

 in the Stati^ >unt of Scotland (1796), xvn. p. 458, to 



occurred t Kenmore on I2th September 1784, con- 

 tinuing in a i 1 degree f"i f..ur days, and again mi i ;th 

 July i;<M- Kenmore lies ;i t the north-eastern end of the lake. 

 the river lay tend 1mm it. It lies .,t the end of a 



B. III. 20 



