212 On the Tides in the great North American Lakes. 
deep arm of the Lake. The extent of Lake Superior is not equal 
in length to the course here described, and that lake, excepting the 
projection of Keewuna Point, presents but few littoral features which | 
“ay have any sensible influence on the elevation of a tide-wave. 
_ But it must be borne in mind, in reference to this subject, that the 
planetary attraction, on reaching the eastern point of these lakes, 
having brought with it no “wave,” has there to begin with an initial 
force, and that it must pass over a considerable portion of the water 
before its operation can be felt. We cannot say at what distance 
from the eastern shore this point of sensible effect would be found; 
: but, if Lake Huron were an isolated lake, we should probably look 
4 
for no lift of the surface, from this cause, even at the western side. 
The tide-wave, therefore, when it arrives at the Straits of Mackina, 
is, notwithstanding the favoring approximation of the two shores, 
probably nearly or quite insensible. It is well known that, although 
__ urrents and counter currents have been long noticed in these straits, 
1¢ has ever regarded them as possessing any of the character 
istics of a lunar tide. Even the fact stated by Charlevoix, and to 
which Mr. Schoolcraft alludes in his travels, of his boat floating on@ 
way while the wind blew the reverse, may be satisfactorily explained. 
A continuous and strong wind prevailing either way through the straits, 
will propel so much water out of one lake into the other, as to destroy 
the equilibration of surface; when the refluent tendency of the ef 
cumulated mass will produce a counter current, though the wind 
may remain unchanged and unabated. Hence Charlevoix’s boat 
may have been “carried against a head wind.” 
If then it be probable that there is no sensible tide at the Straits of 
Mackina, Lake Michigan, including Green Bay, must be considered 
as deriving little or no assistance, in forming its tide-wave, from 4 
sister lake. That it would exhibit this phenomenon, if it stood alone, 
few would be inclined to believe, notwithstanding all auxiliary OP _ 
cumstances, of the chain of islands, and the tunnel form of the a: 
Indeed, Lake Michigan, though favorable for the increase of a wav? 
sent into it from Lake Huron, yet, from its comparative shallowness 
and diminutive breadth, seems unfavorable to the formation of one 
on its own bosom. ‘agi oe * ed 
At is not to be assumed that planetary influences are wholly ee i" 
ative on the lake waters. They undoubtedly have their due effect. Cu 
But that effect is probably nearly or quite insensible. If acalmcou™ 
ni 
