SEICHES IN THE LAKE OF GENfiVAi £05" 



may be obferved by taking notice of fome part of the bank 



where a gently riling fand may render the changes of level 



more conspicuous. The variablenefs of the weather at theltmuft be more 



i'pring and autumn, by occafioning more frequent changes in fp5ng C and'ail- 



the quantities of water, and confequently in the ftate of the tumn. 



rivers above and below the lakes in queftion muft render the 



feiches more frequent and extreme at thefe times. They will 



alfo be moil evident at the ends of a long lake; and the other 



circumftances will be modified by events that for the moft part 



wjould require to be afcertained by obfervations of the local 



circum fiances and events on the (pot. 



The diftinct poriions of rough and fmooth furface called The dlftin& 

 fontaines, which are obferved on the lakes, are very ft rikingly j^ ot " ° Bd 

 leen at fea whenever a breeze fprings up after a dead calm, rough furface on 

 This effeel is very remarkable, and may perhaps be accounted ^Uti^ZVJux 

 for on the fuppofition that the incipient motions of the air may a calm. 

 be attended with eddies that may a 61 more ftrongly on one part 

 of the furface than another. This however does not feem re- 

 concileable with a certain fteadinefs of appearance with which 

 the fmooth and rough furfaces continue diftincl from each other 

 for certain lengths of time. I am not much fatisfied with the 

 conjecture which offered itfelf to me, or which may have been 

 mentioned by fome other perfon when I was at fea many years 

 ago; but it at leaft deferves to be noticed here. It is well 

 known, that the wind fcarcely takes hold of water which is 

 covered with any oily film, and from the experiments of Frank- 

 lin and others we have learned that a fingle drop of oil will Suppofed to arife 

 rapidly fpread over a large furface of water, and caufe all the fron ? 01 ' y .^"2 

 fmail primary waves to fubiide, rendering the furface extremely the water, 

 fmooth. It feemed to me not unlikely that oily matter from 

 animal remains might rife to the furface of the fea during a 

 calm and fpread ilfeif irregularly over certain parts, which 

 would continue fmooth for a confiderable time after the light 

 commencing breeze had ruffled the other parts. I think from 

 recollection that this appearance could not have lafted more 

 than a quarter of an hour; but it is very common, and I often 

 faw, it. May not a fimiiar caufe produce the appearance in —of the lake 

 tfae lake of Geneva. alfo - 



The fonorous reports refembling difcharges of artillery feem The fonorous 

 very likely to arife from the extrication of gas at the bottom reports refem- 

 of the water, wrych rifes and breaks at the furface. I have f u ' ppo fed to be 



HO made by gafes. 



