When The
Waves Scintillate With Bright Green Sparks, I Believe It Is
Generally Owing To Minute Crustacea.
But there can be no
doubt that very many other pelagic animals, when alive, are
phosphorescent.
On two occasions I have observed the sea luminous at
considerable depths beneath the surface. Near the mouth
of the Plata some circular and oval patches, from two to
four yards in diameter, and with defined outlines, shone with
a steady but pale light; while the surrounding water only
gave out a few sparks. The appearance resembled the reflection
of the moon, or some luminous body; for the edges were
sinuous from the undulations of the surface. The ship,
which drew thirteen feet of water, passed over, without
disturbing these patches. Therefore we must suppose that some
animals were congregated together at a greater depth than
the bottom of the vessel.
Near Fernando Noronha the sea gave out light in flashes.
The appearance was very similar to that which might be
expected from a large fish moving rapidly through a luminous
fluid. To this cause the sailors attributed it; at the
time, however, I entertained some doubts, on account of the
frequency and rapidity of the flashes. I have already
remarked that the phenomenon is very much more common
in warm than in cold countries; and I have sometimes imagined
that a disturbed electrical condition of the atmosphere
was most favourable to its production. Certainly I
think the sea is most luminous after a few days of more
calm weather than ordinary, during which time it has
swarmed with various animals. Observing that the water
charged with gelatinous particles is in an impure state, and
that the luminous appearance in all common cases is produced
by the agitation of the fluid in contact with the atmosphere,
I am inclined to consider that the phosphorescence is
the result of the decomposition of the organic particles, by
which process (one is tempted almost to call it a kind of
respiration) the ocean becomes purified.
December 23rd. - We arrived at Port Desire, situated in
lat. 47 degs., on the coast of Patagonia. The creek runs for
about twenty miles inland, with an irregular width. The
Beagle anchored a few miles within the entrance, in front of
the ruins of an old Spanish settlement.
The same evening I went on shore. The first landing in
any new country is very interesting, and especially when, as in
this case, the whole aspect bears the stamp of a marked and
individual character. At the height of between two and
three hundred feet above some masses of porphyry a wide
plain extends, which is truly characteristic of Patagonia.
The surface is quite level, and is composed of well-rounded
shingle mixed with a whitish earth. Here and there scattered
tufts of brown wiry grass are supported, and still more
rarely, some low thorny bushes. The weather is dry and
pleasant, and the fine blue sky is but seldom obscured. When
standing in the middle of one of these desert plains and
looking towards the interior, the view is generally bounded
by the escarpment of another plain, rather higher, but equally
level and desolate; and in every other direction the horizon
is indistinct from the trembling mirage which seems to rise
from the heated surface.
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