The particles were so minute as easily to pass through
fine gauze; yet many were distinctly visible by the naked eye. The
water when placed in a tumbler and agitated gave out sparks, but a
small portion in a watch-glass scarcely ever was luminous.
Ehrenberg states that these particles all retain a certain degree
of irritability. My observations, some of which were made directly
after taking up the water, gave a different result. I may also
mention, that having used the net during one night, I allowed it to
become partially dry, and having occasion twelve hours afterwards
to employ it again, I found the whole surface sparkled as brightly
as when first taken out of the water. It does not appear probable
in this case that the particles could have remained so long alive.
On one occasion having kept a jelly-fish of the genus Dianaea till
it was dead, the water in which it was placed became luminous. 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.
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