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A P P E N D I X . 287
Java; on that of Sumatra.; at Ceylon; at the Laccadiva Islands;
at the SeycheUes; on the coast of Madagascar; and at Amsterdam
Island, at twelve : but at the Chagos Islands and Mauritius it is
high water at about nine, and at the Keeling Isles about eleven.
Here, then, it would seem that there is cause for much perplexity.
Havuig now stated the principal facta which occur to my mind, I
wiU mention the conclusions drawn from them, and then attempt to
explain the anomalies.
Let E G (fig. 1.) represent a section of our globe, of which A B
C D is supposed to he land, and E F G H water. Let H M show
the direction in which the moon's attraction would operate. Tlie
eifect of her attraction, according to Newton's demonstration, would
be to raise the water at F by positive attraction of the water, and at
H by attractmg the earth more than the water :—let tlie dotted line
represent the consequent figure of the ocean.
In fig. 2, let the ocean be supposed 90° or six hours wide ; let the
moon act in the direction M F ; and let the dotted line represent the
altered position of the water when moved out of its natural position
(with respect to the earth) by the moon's attraction.
Agam, in fig. 3, suppose the moon acting in the line M K, and
the dotted line representing the figure taken in that case by the
ocean.
It wiU occur to the reader that but little water can rise at F
and H (fig. 1), at F (fig. 2), or at K (fig. 3), unless water falls or
sinks, at E and G (fig. 1), G (fig. 2), F and G (fig. 3), because
water is butslightly compressible, except under extraordinary pressure,
and because it is incapable of bemg stretched; therefore, if at any
place the sea is raised above its natural level, the excess must be
supplied by a sinking taking place elsewhere. There cannot be a
void space left under the sea between the water and its bed; and
there is no lateral movement of the particles at the surface only
of the ocean sufficient to cause high tides on either shore:—
therefore the conclusion may be drawn, that the whole mass librates
or oscillates.
By llbrating I mean such a movement as that which a large jelly
would have, if its upper part were pushed on one side, and then
allowed to vibrate while the base remained fixed : and by oscillating
I mean a movement like that of water in a basin, after the basin is
gently tUted and let down again : and that such a motion would be