ty of the sea. The pale spectres below the surface
sink deeper, and are lost to sight, but the increasing waves are
tinged here and there with green and white, and often along a line,
where the fresh water is mixing with the salt in an estuary, there is
a brightness so intense that boats and shores are visible.... But if
such sights are to be seen on the surface, what must not be the
phosphorescence of the depths! Every sea-pen is glorious in its light,
in fact, nearly every eight-armed Alcyonarian is thus resplendent, and
the social Pyrosoma, bulky and a free swimmer, glows like a bar of hot
metal with a white and green radiance."

Such accounts are enough to indicate how varied and how general a
phenomenon is the phosphorescence of the sea. To take notice of one
tithe of the points of interest summed up in the paragraph just quoted
would occupy many pages, and we must therefore confine the attention
to a few of the most interesting facts relating to marine
phosphorescence.

We will return to that form of marine luminosity to which we first
referred: what is known as the general or diffused phosphorescence of
the sea. From this mode of describing it the reader must not infer
that the surface of the ocean is ever to be seen all aglow in one
sheet of continuous light. So far, at least, as was ever observed by
M. de Quatrefages, who studied this phenomenon carefully and during
long periods on the coasts of Brittany and elsewhere, no light was
visible when the surface of the sea was perfectly still. On the other
hand, when the sea exhibits in a high degree the phenomenon of
diffused phosphorescence no disturbance can be too slight to cause the
water to shine with that peculiar characteristic gleam. Drop but a
grain of sand upon its surface, and you will see a point of light
marking the spot where it falls, and from that point as a centre a
number of increasing wavelets, each clearly defined by a line of
light, will spread out in circles all around.

The cause of this diffused phosphorescence was long the subject of
curiosity, and was long unknown, but more than a hundred years ago (in
1764) the light was stated by M. Kigaut to proceed from a minute and
very lowly organism, now known as _Noctiluca miliaris_; and subsequent
researches have confirmed this opinion. This Noctiluca is a spherical
form of not more than one-fiftieth of an inch in size, with a slight
depression or indentation at one point, marking the position o