the Great Lakes of America. 293 



quarters. The minimum of rise within the period during which 

 the observations were made was as much as eight inches. The 

 maximum of rise within the same period was as much as forty 

 inches. Mr Lecuyer, a gentleman equally intelligent, expres- 

 sed the same opinion as to a tide at Green Bay. 



If these exhibitions of a flux and reflux of the lakes were 

 only occasional and incidental, not uniform and periodical, 

 there would be perhaps no great difficulty in assigning satis- 

 factory causes. The Seiclies of the Lake of Geneva have been 

 ascribed by Mr Bertrand to the influence of electrical clouds 

 which attract and raise the waters of the lake, and he supposes 

 that this water afterwards falling, produces those undulations 

 of which the eff*ect, like that of the tides, is most sensibly felt 

 where shores are most approximated. 



A more probable cause may be the unequal pressure of the 

 atmosphere on the waters, which will of course rise higher as 

 the weight of the incumbent air is less, and fall as it becomes 

 greater ; and these changes being almost always in operation 

 may account for the almost continual ebb and flow of the 

 lakes. 



The cause assigned by Charlevoix is entirely unsatisfactory ; 

 and it is premature to form a theory on the subject. Facts and 

 experiments ought to precede speculations ; and we must leave 

 it to future inquirers to ascertain the facts in extenso — to in- 

 vestigate the causes, and to determine whether this phenome- 

 non be owing to the pressure of the atmosphere — the influence 

 of the moon — the attraction of the clouds — the convexity or 

 motion of the globe, or any other assignable agency. 



% There is an annual rise and fall of Lake Erie. The rise 

 generally commences in March, and terminates about the mid- 

 dle of July ; and this is the case sooner or later with the other 

 lakes. It is owing to the great accession of water produced by 

 the melting of snow and ice, and by the vernal rains ; and the 

 fall is occasioned by the failure of most of these sources of sup- 

 ply in summer. 



3. There is, besides the annual rise of the lakes, a more ex- 

 tended periodical one, at least every three years, and then a 

 correspondent declension. Some extend the time to five, and 

 others to seven years. Some sa}? that the highest rise is seven 



