302 Astronomical and Nautical Collections. 
quired for a wave to trayel round it would be equal in all latitudes, 
and the tides would be of the same species in every part; while 
the tides of the atmosphere, on the other hand, independently of the 
resistance, would be indirect at the equator, and direct near the 
poles. 
“* However the primitive oscillation may be constituted, it is easy 
to understand, that it will be propagated through a limited channel, 
connected with the main ocean, in a longer or shorter time, ac- 
cording to the length and depth of the channel; and that if the 
channel be open at both ends, the tide will arrive at any part within 
it by two different paths ; and the effects of two successive tides 
may in this manner be so combined as to alter very materially the 
usual course of the phenomena: for instance, if there were about 
six hours’ difference in the times occupied in the passage of the two 
tides over their respeciiye paths, the time of the high water be- 
longing to one tide would coincide with that of the low water 
belonging to the other, and the whole variation of the height might 
in this manner be destroyed, as Newton has long ago obseryed with 
respect to the port of Batsha: and it may be either for a similar 
reason, or from some other local peculiarity of situation, that no 
considerable tides are observed in the West Indies; if indeed it is 
true, that the tides are so much smaller there than might be ex- 
pected from calculation ; for in fact the original tides of an open 
sea, not exceeding a mile or two in depth, would amount to a few 
inches only, even without allowing for the effects of resistance. In 
the middle of a lake, or of a narrow sea, there can be little or no 
primitive elevation or depression; and the time of high water on its 
shores must always be about six hours before or after the passage 
of the luminary over the middle ; so that from this source we may 
derive an infinite diversity in the times at which these vicissitudes 
occur in different parts. 
“« The effects of resistances of yarious kinds, in modifying the 
time of high water, cannot easily be determined in a direct and 
positiye manner from immediate observation, Mr. Laplace ap- 
pears to be of opinion that these resistances are wholly inconsider- 
able ; but if any dependence can be placed on the calculations of 
