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28-1 A P P ENDI X .
In the greatest expanse of ocean, that whicli meets with only partial
interruption to free tidal movements—the zone, if it may he so
called, near fiftj'-five degrees of south l a t i tude - the r e is high water at
opposite sides, and low water at opposite sides of the globe nearly
at the same time. ,
At the eastern part of the Falkland Islands, exposed to the tide ol
this zone, it is high water, or full sea, at about nine o'clock on the
day of new, or fuU moon, by Greenwich time and on the southern
shore of Van Di emens Land it is high-water at about ten. Thi s is
not a point exactly opposite, it is ti-ue, but it is the nearest so at
which we have yet obser\-ed.
At each of these places the tide rises sLx hours and falls six hours,
alternately ; therefore when it is low water at one, it is also low water
at the other. 'Hiere is no intermediate place in this zone, rather
distant from these points, at which I know of a tide observation
deser,™g confidence; but those above-mentioned are certain, and
corroborate the Newtonim theory in a satisfactory manner
Thi s is, however, the only zone of ocean, which is at all able to
follow the laww%ieh would govern its undulations if the globe were
covered « i t h water. In other zones (taking about ten degrees
in latitude as a zone) it is Ug h water, generally speakmg, at one
side of an ocean near the time that it is low on the other.
In oceans about ninety degrees wide, tliis happens very nearly;
but as the ^-idth diminishes, so do the times of high water at each
side approach ; and as the width increases beyond ninety degrees, as
in the case of zones of the Pacific, the times of high water stiU
approach (in consequence of the tendency to high water at opposite
points), and farther confirm the Newtonian theory.
For examples (on the day of fuU moon) : - I n the Pacific, at Port
Henri' m 50° S . it is high water at 5h. at which time it is near low
water at Auckland Island, where the time of high tide is 12h 30m.
In this case, the interval between one high water, and the other on
the opposite side of the ocean, is 7h. 30m. or 4.30 ; and the width of
that ocean is nearly eight hours (measured m time.)
At Valdivia, in lat. 40» S . it is high water at 3h. 30m. and at New
Zealand, on that parallel, at 9h. 50m. The space of ocean between
is seven hours nearly : the differences are 6.20 and 5.40.
• To « hich all the times are here reduced for easy comparison.
AP L ' EXDIX. 2 8 5
In 30° S . at Coquimbo, it is high water at 2h. and at Norfolk
Island it is high at about 9h. The intermediate space of ocean is
nearly eight hours wide.*
In 20° S. , at Iquique, it is high water at Ih. 30m., and at New
Caledonia, in the same parallel, it is high water at 9h. I5m. The
space between is about eight hours wide : the least chffcrence 4.15.
Near 10°, or 12°, at Callao, it is high water at about t en; but
as on this parallel a multitude of islands spread across half the
Pacific, no comparison of times can be trusted.
On the equator—at the Galapagos Islands—it is high water at
8h. 2 0m. ; and at New Ireland it is high water at 3h. 0 0m.—a difference
of seven hours nearly. The ocean is here eight hours wide ;
but at New Ireland there is only one tide in twenty-four hour s—an
anomiily to be considered presently.
The parallel of 10° N. is similar to that of the equator—however,
we may as well examine it. At the little Isle of Cocos, and at Nicoya,
on the main, it is high water at about 8h. ; and at the Philippine
Islands, in the same latitude, at 4 h . ; the difference, eight hours, is
not far from the meridian distance, which is about ten hours ; but the
Philippines also feel the effects of causes which influence the tides
at New Ireland, and, generally, those of the Indian Archipelago.
In 20° N. at San Bias, it is high water at 3h; and at Loo-choo,
the neai-est known point of comparison at the other si<? of the ocean,
at lOh. The difference, 7 hom's, is about an hour less than the
meridian distance. In 30° N. on the Coast of California, it is high
water at 4h., and at Nangasaky, in J apan, in lat. 32° 44', at 11.12.
The difference, 7.12, is nearly half an hour less than the meridian
distance. lu 40° N. it is high water at about Sh. on the American
coast, but for the opposite shore I have no data. In 50° N. it is high
water on Vancouver Island at 9h., and at the south extreme of Kamschatka
it is said to be high water at about 6h. ; the difference. 9 or
3 hours, is anomalous—made so probably by a derivative tide.
Having examined the Pacific, let us proceed in a similar manner
with the Atlantic, and the Indian Oc e a n ;—
In 40° S . off Blanco Bay, the time of high water is 9h. ; the
same as at the Falklands.
At Amsterdam Island, orie authority says 6h., another 12}i, for the
• A derivatiNC tide (p. 289) may act here.
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