Among the phenomena which have long exercised the sagacity of
philosophers, that of the luminous appearance of the surface of the sea,
during the obscurity of the night, is highly curious. A variety of
experiments were made by a French naturalist at Cayenne, at different
seasons, to ascertain its true cause; and to him it appeared that these
luminous points were produced by motion and friction alone, as he could
not, with the help of the best glasses, perceive any insects floating in
the water. But it would seem, from the experiments and observations of
many learned men, that this phenomenon is produced by various causes,
both jointly and separately. It has been proved by one set of
experiments, that the putrefaction of animal substances produces light
and scintillation in the sea. A little white fish placed in seawater
rendered it luminous in the space of twenty-eight hours. On another
hand, it is certain that there is in the sea a prodigious quantity of
shining insects or animalcules, which contribute to this phenomenon. A
French astronomer, M. Dangelet, who returned from Terra Australis in
1774, brought with him several kinds of worms which shine in water, when
it is set in motion; and M. Rigaud affirms, that the luminous surface of
the sea, from Brest to the Antilles, contains a great quantity of
little, round, shining polypi, of about a quarter of a line in diameter.
Other learned men, who acknowledge the existence of these luminous
animals, can not, however, be persuaded to consider them as the cause of
all that light and scintillation which appear on the surface of the
ocean. They imagine that some substance of a phosphoric nature, arising
from putrefaction, must be admitted as one of the causes of this
phenomenon. By other naturalists it has been ascribed to the oily and
greasy substances with which the sea is impregnated; in proof of which a
kind of fish, resembling the tunny, is cited, as being provided with an
oil which shines with considerable luster.
The Abbe Nollent was convinced, by a series of experiments, that this
phenomenon is caused by small animals, either by their luminous aspect,
or by some liquor or effluvium which they emit. He did not, however,
exclude other causes; and among these, the spawn or fry of fishes is
deserving of attention. M. Dangelet, in sailing into the bay of
Antongil, in the island of Madagascar, observed a prodigious quantity of
fry, which covered the surface of the sea for the extent of more than a
mile, and which he at first, on account of its color, mistook for a bank
of sand. This immense accumulation of spawn or fry exhaled a
disagreeable odor; and it should be remarked that the sea had, for some
days before, appeared with uncommon splendor. The same accurate
observer, perceiving the sea remarkably luminous in the road of the cape
of Good Hope, during a perfect calm, remarked that the oars of the
canoes produced a whitish and pearly kind of luster: when he took in his
hand the water, which contained phosphorus, he discerned in it, for some
minutes, globules of light as large as the heads of pins. On pressing
these globules, they appeared to his touch like a soft and thin pulp;
and some days after the sea was covered with entire banks of small
fishes, in innumerable multitudes.
From all these facts it may be deduced, that various causes contribute
to the light and scintillation of the sea; and that the light which the
Cayenne naturalist attributed to agitation and friction, differs from
that which is extended far and near, seeming to cover the whole surface
of the ocean, and producing a very beautiful and striking appearance,
particularly in the torrid zone, and in the summer season.