218 On the Tides in the great North American Lakes. © 
Se a 
e task of observation was entrusted. Full confidence may 
however be placed in these memoranda. a 
The slightest inspection will satisfy you, that the changes inthe = 
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 ¢ s to me is the result of calculation, when the laws, — 
which regulate solar and Junar attraction, and the limited sphere o 
_ their operation, are taken into view. And the conclusion is for fied 
by analogy ; for in the Baltic, the Black Sea, and the Caspian, 2 
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, will 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 explan® 
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 He 
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 mout 
of the bay towards the head, until it attains-its maximum elevatlo?s 
and in the mean time, the operation of the same cause will propel the | 
water of Lake Michigan towards Chicago. There will conseque y 
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 uppet put 
the bay. For the wind, it will be recollected, is still sweep!" be 
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 * 
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