168 TRANSACTIONS OF THE SOCIETY OF PHYSICS AND 



duced to tlie uniform of 10 feet below tlie mark of the stoue of Niton, 

 the calculations for tbe tbirty-six years have given the following results: 



The lake attains its minimum (3 feet) on the lltli of February, audits 

 maximum (7 feet) on tbe 7tb of August. There is a first mean level 

 from the 28th to tbe 29tb of May, and a second from tbe22d to tbe 23d of 

 October. The level is then during 218 days above, and during 147 days 

 below the mean. Tbe level rises more quickly than it sinks. The rising 

 is most rapid toward tbe 19th of June ; it rises then 6 inches a day. 



To show the annual variations, M. Plantamour has traced tbe curves 

 of the highest levels of the means and of tbe lowest waters. These 

 three curves have some analogy between them, but are far from con- 

 cording. The level of tbe highest water varies tbe most from year to 

 year, and it influences the meau more than tbe low water. The mean of 

 tlie high tvafers has not sensibly varied during the lapse of thirty-six years. 

 The bigbest maximum (9 feet) was attained on tbe 17th of July, 1846. 

 Tbe level of tbe low water in winter is, on the contrary, raised progres- 

 sively. The lowest minimum (1 foot 3 inches) is sbown on the 5th of 

 April, 1840. That of 1873-1874, wbicb astonished the public, remained 

 Ki inches above the level of 1840. As to tbe elevation of tbe low water 

 during recent years, one of our colleagues, a former member of the ad- 

 ministrative council of the city of Geneva, calls attention to tbe fact 

 that tbe position of tbe suction-pipe of the hydraulic machine has not 

 been altered for twelve years. Professor Plantamour, in this work, 

 wbicb has required long calculations, has limited himself to the exposi- 

 tion of the figures, but any one aware of tbe discussions wbicb have 

 arisen at various times upon the supposed effects of the different levels 

 of tbe lake, cannot abstain from one satisfactory reflection. The high 

 water is frequently complained of, but never the low water, unless it 

 sinks to such a point as to interfere with navigation, and, in some cases, 

 with the approach to tbe ports. It is pleasant, then, to know that the 

 high water has not risen for thirty-six jears, and that the mean of the 

 low water is rather higher than lower.* 



The investigations in regard to Lake Leraan have been continued in 

 a most satisfactory manner since our society and the Vaudois society of 

 the natural sciences have united in encouraging them. Prof. Fran9ois 

 Forel, who bad been previously engaged with tbe subject, and (lontinues 

 to pursue it, has communicated to us a series of observations of great 

 interest. I have already mentioned those relative to the absorption of 

 light by the waters of the lake. He also made some upon tbe seiches, or 

 sudden variations of level, very perceptible in tbe narrow jiart of tbe lake 

 near Geneva. We know that Professor Vaucber attributed the phe- 

 nomenon to the variations in the weight of the atmosphere.t M. Forel, 

 while confirming the observations and the opinions of this savau, has 



* Oar M6inoircs alroady contain numerous documents upon the level of the lake. See 

 V, p. 63 ; vol. viii, p. 119 ; vol. x, p. ;]27. 

 ] Miinoircs of the society, vol. vi, p. 35. 



