26 Tides in the North American Lakes. 
the head of Green Bay as the point where they would show 
themselves in the greatest fullness. ‘The course of planetary at- 
traction, operating on a line from east to west, would traverse a 
space of from four hundred and fifty to five hundred miles.” 
And further, he remarks, that ‘the configuration of the coasts 
too, through which the line passes, would appear to lend much 
extraneous aid, to give whatever wave might be formed an un- 
due elevation.” j 
I fully concur in the opinion advanced respecting the position 
at Green Bay, as one favorable for observations, but an inspection 
of the outline of the lakes and straits operated on, convinces me 
that the phenomenon would be retarded and diminished by the 
irregularities and sharp projections, instead of being increased, as 
inferred by the gentleman quoted. 
It has been, I believe, satisfactorily demonstrated, that certain 
periodical undulations, induced by planetary influence, constitute 
tides, attended, of course, with local superficial translation. It is 
to be observed, that when the sun and moon act in conjunction, 
or opposition, the attractive force, being then most powerful, the 
result must be the most evident; and when the moon is in quad- 
rature, that attractive force becomes the least possible, yet never 
so slight as to induce the belief, that the phenomenon has ceased ; 
still possessing, therefore, the characteristics of a tide. Now, in 
continuation of this view, we observe that the variable and often 
cramped configuration of the coast, united with the alternate deep 
and shallow water, and also the islands which so strongly guard 
the entrance to Green Bay, tend manifestly to impede undulation, 
as well as to limit the influence of local translation; therefore 
these fixed and permanent modifying causes, being a constant 
quantity, the variable influence of planetary attraction, must, 
when slight, be almost neutralized, with great irregularities at- 
tending the results; and only when great present the most satis- 
factory evidence of cause and effect. 
The low specific gravity of lake water, varying very little 
from unity, renders it less subject to planetary influence than sea 
water, and more liable to the action of the winds; moreover the 
majestic current of the whole body of lake water, collected from 
innumerable rivers, is diametrically opposed to the course of plan- 
etary attraction, having a direct tendency to modify results. 
