S82 ArPENDlX.
APPENDIX. 283
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the moon upon a body of water, by wMeh any
to^-ards her before she is verticaUy over it, as well as after she has
nassed to the westward of the meridian of that portion.
' X t Me attention appears to have been paid to a consrderahon
of 1 momentum acquired by any great body of water moved from
1 position it would oeeupy if undisturbed, and to the eonsequenees
ment. Andthere seems to be a difficulty in altogether r e c ^ c dmg ^
I t e m e n t that " tides are diminished by difcsmn,* wrth the m ^ n r
r w U e h the great tides of the Northern Atlantic are supposed o
belted-asfppoBitionwhiehismdrdydependentuponthepnncple
„f vibrations or osclllations."t .
In ~ n c e of similar ideas, excited by the facts previously
m e n t i o n e ^ L following questions were ii^erted in the Geographical
' " " ^ t l n t ; appetTresumption in a plain sailor attempting to offer
an idea oi L o on the difficult subject of 'Tides;' yet, with he
r j o s t dlrence to those who are competent to - o n ^
subject, I w-iU venture to ask whether the supposition of Atlantic
t w t b ing principally caused by a great tide-wave «
s t t h e r n oLan, is not a Uttle difficult to reconcile with the facts that
f h T r t r v e r y lit^e tide upon the coasts of Bra.a Ascension, ^ d
o Z e a , and that in the mouth of the great river Plata there is httle
" " c ^ ^ l c h ocean have its own tides, though affecting, and being
wen as upward, after and towards the moon as she passes ? If so,
: ^ e r L T o o n has passed, will n6t the mass of that ocean have ^
^terTy inclination to regain that equilibrium (with respect to th
L n e ) from which the moon disturbed it (sun's action not
C S n t ^ i t s equilibrium, would not its own momentum c . ^
it too far east;-ard; and would not the moon's action be agam
^ " ^ ' X t n t p a r t of an oceanhaveawestwardtendency.while anther
part, which is wider or narrower, from ea.t to west, has an eastward
• Whewell's Essay, p. 217-
t Herschel's Astronomy, Cab. Cyc.p. 334.
movement ? If so, many difficulties would vanish ; among them those
which were fii'st mentioned, and those perplexing anomalies on the
south coast of New Holland."—(Jour. R. Geog. Soc. vol. vi. part 11.
p. 336.)
It might have been concluded that these questions had scarcely
been noticed, as I heard nothing on the subjeqit, had I not lately read
the following remarks in a work published in 1837. Whether their
author ever saw the questions, I do not know; but as his observations
bear strongly upon the subject, and are those of an eminent mathematician,
I quote them verbatim
" Suppose several high, narrow strips of land were now to encircle
the globe, passing tlirough the opposite poles, and dividing the
earth's surface into several great, unequal oceans; a separate tide
would be raised in each. When the tidal wave had reached the farthest
shore of one of them, conceive the causes that produced it to
cease; then the wave thus raised would recede to the opposite
shore, and continue to oscillate until destroyed by the friction of its
bed. But if instead of ceasing to act, the causes which produced
the tide were to re-appear at the opposite shore of the ocean, at the
very moment when the reflected tide had returned to the place of its
origin, then the second tide would act in augmentation of the first;
and if this continued, tides of great height might be produced for
ages. The result might be, that the narrow ridge dividing the adjacent
oceans would be broken through, and the tidal wave traverse a
broader tract than in the former ocean. Let us imagine the new
ocean to be just so much broader than the old, that the reflected tide
would return to the origin of the tidal movement half a tide later
than before ; then instead of those two super-imposed tides, we should
have a tide arising from the subtraction of one from the other. The
alterations of the height of the tides on shores so circumstanced might
be very small, and this might again continue for ages, thus causing
beaches to be raised at very different elevations, without any real
alteration in the level, either of the sea or land."—(Babbage's Nmth
Bridgewater Treatise, pp. 248, 249.)
Additional data,, and leisure to reflect upon them, have tended to
confirm the view taken previously to asking those questions in the
Geographical Journal; but before stating this view more explicitly,
it is necessary to lay facts before my readers, from which they may
judge for themselves.
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