Great North American Lakes. 81 
as depth of the lake. In the case of a direct tide, the time 
of the passage of the luminary over the meridian must coin- 
cide with that of high water, and in the case of an inverted 
tide, with that of low water. , 
ist ler that the height of the inverted or remote lunar 
tides may be five feet, or equal to that of the primitive tides, 
the depth of the open sea must be six and a half miles; and 
and if the height is only two feet, which is perhaps not far 
from the truth, the depth must be three and five-seventh 
miles. 
“ The tides of alake, or narrow sea, differ, materially, 
from those of the open ocean, since the height of the water 
scarcely undergoes any variation, in the middle of the lake ; 
it must always be high water at the eastern extremity, when 
it is low water at the western: and this must happen at the 
time, when the places of high and low water, with respect 
to the primitive tides, are equally distant from the middle of 
the lake. [Figs. 1. 2. and 3. from Plate 38 
“The tides may be direct, in a lake, one hundred fathoms 
deep, and less than 8° wide; but if it be much wider, they 
must be inverted. 
‘“‘ Hitherto we have considered the motion of the water as. 
Fig. 1. “The dotted ellip- 
sis shows the section of a 
sea, if it were always ina 
state of equilibrium, with the 
attraction of a distant body ; 
and the dark ellipsis, the ac- 
tual form assumed, in conse- 
oo 
Vor. 2vi—Ho.-h..” 11 
