300 On the Seiches of the Lake of Geneva. 



of the water which supported it ; and finally, the change might 

 even in certain cases be the very contrary to that which the va- 

 riation of the mercury in the same place, and at the same mo- 

 ment, might require. In truth, no one can pronounce any thing 

 upon the possible movements of the water in the spot where the 

 observations are making, without at the same time knowing the 

 condition of the neighbouring columns. And even were we to 

 suppose that many individuals were observing in different places 

 at the same moment, still their number could never be so multi- 

 plied as to obtain in this particular precise and accurate informa- 

 tion. We ought, then, to be satisfied with the knowledge, that 

 the weight of various columns may vary, and frequently in rea- 

 lity do vary, and that it is impossible for them so to vary, with- 

 out disturbing the level of the water ; so that, could we even ac- 

 count for the occurrence of the seiche from some other cause 

 than the atmospherical variations, we should still have to explain 

 how the diflPerent columns of air could vary unequally in weight, 

 whilst the water on which they reposed did not itself vary in 

 height. 



However, it at one time did happen that I was more for- 

 tunate in this particular than could have been expected. Dur- 

 ing the tempestuous weather which brought the month of No- 

 vember 1803 to its close, and during which the barometer and 

 the temperature varied nearly equally alike, Sunday the 13th 

 was of whole time the most remarkable. At three o'clock in 

 the afternoon of that day there had been lightning, to which 

 succeeded, in about half an hour, rain, accompanied with tre- 

 mendous wind. I happened to be at Eaux-Vives at the moment, 

 and I observed one of the most remarkable seiches which I have 

 ever seen ; the water gradually lowered itself about a foot, and 

 it was still descending when I left the spot. This happened 

 exactly at the same time that certain of my friends had been ob- 

 serving the barometer, and who had previously observed it to 

 vary considerably during the course of the day : at this precise 

 time they saw it descend suddenly almost a line, and continue 

 its oscillations for a considerable time afterwards. 



The local and instantaneous variations of the barometer be- 

 ing, under ordinary circumstances, to the extent of about j^ 

 of a line, and reaching to a line, or even more, at the approach 



