An introduction to astronomy: designed as a text-book for the use of students in college. By Denison Olmsted ...

or full moon. As tile interval for ally given place is always
ne arly the same, it becomes a criterion of the retardation of
the tides at that place. On account of the importance to
navingation of a correct knowledge of thle tides, the Britist
Board of Admiralty, at the suggestion of the {Rocyal Society,
recccently issued orders to their agents in various importanlt
naval stations, to ]have accurate observations made -o the
tides, witlI the view of ascertaining the establishment and(
various otlher particula s respecting each station;': and t1he
government of the United States iss proselcuting similar investigations respecting our own p)lorts.
292. According to P'rofessor Whewcell,J' the tides on the
coast of iNort]h America are derived from the great tide-wave
of tlle Soutll Atlantic, whichl run s steadily northward along
th e coast to the mouth of the 3Bay of tFundy, where it meets
tihe northern tide-wae flowing in tile opposite direction..lecnce he accounts fo' tile high tides of the Bay of Fundy.
2933. Tihe largest lfakes rand nlatnd seas have no perceptible
fides. TIis is asserted by all writers respecting tthe Caspian
and E'luxine, and tte same is found to be true of the largest of
th1e iN ortlh American Lakes, 1ake Superior.t
Although these several tracts of water appear larg;c, when
taken by themselves, yet tley) occupy but small portions0 of
the surfatee of tile globe, as will appear evident firom the delineationl of them on an artificial globe. ]Now we must recollect
t.hat the lprilitive tidces are lproduccd by tle uneqgt-al action of
tle sun antid moon upon the diflerent parts of the earth; and
tlhat it is only at points whose distance from each other bears1 a
considerable ratio to thle whole dlistance of tile sun or the llmoon,
that thlte inlquality of action becomes mlanifcst. Thlte space requiiled is larger thlan either of these tracts of water. ]t is
obvioull also, that thel have n\o opportunity to be subject to a
decivativo tiICe.
294. To apply the theory of universal gravitation to all
rlubbock, lipore onl thle Tides, 1833. {- Phil. Trans., 1833, p. 112.
+ See Exp)rimcnt. of (ov. Class, Am. Jour. Science.