218 On the Tides in the great JVorth American Lakes. 



whom the task of observation was entrusted. Full confidence may 

 however be placed in these memoranda. 



The slightest inspection will satisfy you, that the changes in the 

 elevation of the water are entirely too variable to be traced to any 

 regular permanent cause ; and that consequently there is no percep- 

 tible tide at Green Bay, which is the result of observation. And 

 such it appears to me is the result of calculation, when the laws, 

 which regulate solar and lunar attraction, and the limited sphere of 

 their operation, are taken into view. And the conclusion is fortified 

 by analogy ; for in the Baltic, the Black Sea, and the Caspian, each 

 much larger than either of our lakes, there are no tides, or none wor- 

 thy of observation. The opinion however has long prevailed, and 

 been frequently advanced, that the ebb and flow of the water, which 

 are constantly observed upon the shores of the North American 

 lakes, are tides, governed by the same laws as the tides of the ocean ; 

 and Green Bay has been often referred to as a place affording the 

 most distinct proof of this phenomenon ; and particularly as the rise 

 and fall of the water do not always appear to depend upon the di- 

 rection of the wind. A glance at the features of the bay and lake, 

 and at their relative position, w^ill probably enable us to account for 

 this prevailing error, without calling in question the veracity or judg- 

 ment of preceding observers, or resorting to causes for the explana- 

 tion of the difficulty, which have obviously no connexion with it. 



Lake Michigan is about three hundred miles in length, and about 

 fifty in breadth. Near its northern extremity, it is joined by Green 

 Bay, which is in fact a deep indentation of the lake, nearly parallel 

 with it in its course, and extending perhaps eighty miles into the 

 country. A northerly wind blows up the bay and lake ; and as the 

 former is comparatively small, it will much sooner feel the full effect 

 of the wind than the latter. The water will be driven from the mouth 

 of the bay towards the head, until it attains its maximum elevation ; 

 and in the mean time, the operation of the same cause will propel the 

 water of Lake Michigan towards Chicago. There will consequently 

 be a depression at the mouth of the bay, where the water will con- 

 tinue to ebb, after it has risen to its full height in the upper part of 

 the bay. For the wind, it will be recollected, is still sweeping up 

 Lake Michigan, and driving the water before it. It is obvious 

 that in this state of things a reaction must take place in Green Bay, 

 and that the water will begin to flow towards the mouth, to supply the 

 deficiency, occasioned by the transfer of a part of the contents of 



