The phenomena with this name and that of “Squid” are occasioned by the
presence of phosphorescent animalcules. They are especially produced
in the intertropical seas, and they appear to be chiefly abundant
in the Gulf of Guinea and in the Arabian Gulf. In the latter, the
phenomenon was known to the ancients more than a century before the
Christian era, as may be seen from a curious passage from the geography
of Agatharcides: “Along this country (the coast of Arabia) the sea
has a white aspect like a river: the cause of this phenomenon is a
subject of astonishment to us.” M. Quatrefages has discovered that the
_Noctilucæ_ which produce this phenomenon do not always give out clear
and brilliant sparks, but that under certain circumstances this light
is replaced by a steady clearness, which gives in these animalcules a
white colour. The waters in which they have been observed do not change
their place to any sensible degree.