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“ The circularly-formed Coral Islands in the Pacific occasionally
afford excellent land-locked hai’bours, with a sufficient
entrance, and would be well adapted to any nice astronomical
observations which might require to he carried ou in undisturbed
tranquillity. While these ai-e quietly proceeding, and
the chronometers rating, a very interesting inquiry might be
instituted respecting the formation oi these coral reefs.
“ An exact geological map of the whole island should be
constructed, showing its form, the greatest height to which the
solid coral has risen, as well as that to which the fragments
appear to have been forced. The slope of its sides should be
cai’efully measured in different places, and pai'ticularly on the
external face, by a series of soundings, at very short distances
from each other, and carried out to the greatest possible depths,
at times when no tide or current can affect the perpendicularity
of the line. A modern and very plausible theory has been put
forwai'd, that these wonderful formations, instead of ascending
from the bottom of the sea, have been raised from the summits
of extinct volcanoes; and therefore the nature of the
bottom at each of these soundings should be noted, and every
means exerted that ingenuity can devise of discovering at what
depth the coral fonnation begins, and of what materials the
substratum on which it rests is composed. The shape, slope,
and elevation of the coral knolls in the lagoon would also help
the investigation; and no circumstances should be neglected
which can render an account of the general structure clear and
perspicuous.
“ A set of observations connected with the theory of the
tides might likewise be carried on with peculiar propriety in
one of these coral basins, provided the openings should be
sufficiently wide and deep to admit the ffux and reflux without
material impediment. The island selected for such a purpose
should be nearly midway in the ocean, and not verj- fai- from
the equator. There the tidal wave, uninfluenced by the interrupting
barrier of one continent, and equally far from the
reaction of the other, might be measured with very beneficial
results. Delicate tide-gauges should be prepared beforehand.
and immediately fixed in some snug nook, where the undulation
of the sea could not reach. The rise and fall of the tide
should be registered every hour, during the stay of the Beagle,
as well as the moments (stated whether in apparent or mean
time) of high and low water, as nearly as they can he obtained ;
and the periods at which the sea and land breezes spring up
and fail should likewise be noted, with their effects on the tide,
if they can be detected. A boat should he detached, on each
tide, to some distance from the island, in order to ascertain the
strength and direction of the stream ; and all these operations
should be continued, if possible, through a whole lunation.
“ Compiling general and particular instructions, for the
navigation of all the places which he may visit, will of course
be an essential part of the Commander’s duty ; but he will also
have innumerable opportunities of collecting a variety of
auxiliary information, which, when judiciously combined with
the above instructions, of a purely nautical character, will
much enhance their utility to all classes of vessels. Such as the
general resources on which ships may depend in different
places : the chief productions that can he obtained, and the
objects most anxiously deshed in return : the effect of seasons,
of climate, and of pecuhar articles of food on the health of the
crew, and many others which will readily occur to his mind,
and which become of great value to a stranger.
“ On all the subjects touched on in these memoranda. Commander
Fitz-Roy should be directed to draw up specific reports,
and to transmit them from time to time, through their Lordship’s
Secretary, to the Hydrographic Office, so that if any
disaster should happen to the Beagle, the fruits of the exjjedi-
tion may not be altogether lost. Besides such reports, and with
the same object in view, he should keep up a detailed correspondence
by every opportunity with the Hjffirographer.
“ The narrative of every voyage in the Pacific Ocean abounds
with proofs of the necessity of being unremittingly on guard
against the petty treacheries or more daring attacks of the
natives. I t should be recollected that they are no longer the
timid and unarmed creatures of former times, but that many of
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