448 Prof. Forel on the " Seiches " o/£/j<? /Swtss Lakes. 



In a pamphlet by Dr. J. Rud. Marian, of Basle, ' Ueber 

 die Bewegung tropfoarer Fliissigkeiten in Gefassen/ Basel, 

 1828, which was communicated to me by the grandson of the 

 author, my friend Prof. K. von der Miihle, of Leipzig, I find 

 the formula 



which expresses in function of the length (7) and of the depth 

 (/i) of the basin, the duration t of the motion of oscillation ; t is 

 the duration of a half oscillation of what I have called la seiche 

 haute et la seiche basse, or, la seiche ascenclante et la seiche des- 

 cendante. 



This formula is perfectly applicable to our lake seiches. 



For convenience of calculation I have transformed it into 



wlG") 



irh\2 



+ 1 



and into 



and on applying these formulae to our lakes I find that they 

 express very sufficiently the relations between the duration of 

 the seiches and the dimensions of the lakes. 



I assume at starting that the formula which has been calcu- 

 lated for a basin with a horizontal bottom, is applicable to a 

 basin of irregular depth if for h we adopt the mean depth 

 (Comp. I re e'tude sur les seiches, p. 36). Perhaps this point 

 ought to be submitted to a fresh study. However this may 

 be, I append a few examples of the application of my formulae 

 to the seiches. 



Transversal seiches of Lake Leman . . 2^=600" 



1= 13800 metres * = 300" 



The formula gives A = 216 metres. Now the greatest depth 

 of the lake is 334 metres; and accordingly this value of 216 

 metres for the mean depth of the large lake is perfectly 

 plausible. 



Longitudinal seiches of Lake Leman . 2£=4200" 

 £ = 73200 metres * = 2100" 



