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

170 III it MON.
equal distances lfrom thle tiglhest poilts, alnd thlerefore thle uinmediate tide'3, and the opplositC one'12 arle equal; both are
less, tle higlher tihe latitude, and at the poles there is no tide.
\'Whell tlle mo11on is on tte north side of the equtator, as ill figrc 58, at 1her greatest northern1t declination, a place d(scrib)inlg
tlce parallel'lY wiltl IIhave'3 forl thle tight of tie tide wl lltt
thefl moon is on thle superiorl melidian, anld T'2 for the heighlt
whlen tlie moonl is on thtle inllrior meridian. l'lCereforet, all
pltace.s north of the. equator vill have the highest tide when tell
moion is above the ttorizon, and tlhe lowest w\len sihe is below
it; the difference of thei tides diminishing toward tie equator',
wltcIre they are equal. At tie same time, p)laces soutl of tlhe
equattor have the llighltst oAdes rwhell ti)e lto00ol iS below the
horizon, and thle lowest when sshe is a;bove it. Whent the tmoon
is at; her greatest declination, the liglhest tides will take place
towarSd the tropics. 1Th lcireumstances are all reversed \lwhen
Ilthe mloon is south of the eq. uator.'.'
286g.'IThe motion of the tide-wave, it slhould be relar<ked,
is not a.:riogress ivw_, motion, but l mere undulation, and is to
be ctarefully distinguished fiom t.le currents to which it gi\Cves
rise. If thle ocean enveloped the earnthl and the silun land moon
were at rest in the equator, the tide-wave wou'ld travel at tlhe
samte rate as tito earth on its axis. I(ldced, the correct way of
conceiving of the tides, is first to regardt the moon as at rest,
and the earth as revolving and bringing su ccessive parts under
it, whlichl parts are thlus elevated in succession; and thlen, to
considert the moon and tides as moving east 130 per dayr; thlis
mlaking thle time of tle relative revolution of the tides westward, near 265 instead of 24 holuros.
28 7. Tl he tides of rivers, arrowTi bays, and saores fit-r t'otL
lte main body of the icxasm, are not produceed in those places
by the dfirect action of thle stun and moon, but are subord inate
Mwaves propagated firom tlhe great tide-Nwave.
t,ines drawn tllrough all the adjacent parts of any tract of
water, whlich have lilgh water at, the same time, are called coti(al iines.t'' \re may, for instance) draw a line thllroughl all
EdItin. f;ntccO., Art. IA.'lnoZny, p. 623.
-VWh well, Phil.'transactions fori 1833, p. 118.