Young Folks' Library, Volume XI (of 20) by Various

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Around the Samoa group the water rose and fell once in every fifteen
minutes, while on the shores of New Zealand each oscillation lasted no
less than two hours. Doubtless the different depths of water, the
irregular conformation of the island groups, and other like
circumstances, were principally concerned in producing these singular
variations. Yet they do not seem fully sufficient to account for so
wide a range of difference. Possibly a cause yet unnoticed may have
had something to do with the peculiarity. In waves of such enormous
extent it would be quite impossible to determine whether the course of
the wave motion was directed full upon a line of shore or more or less
obliquely. It is clear that in the former case the waves would seem to
follow each other more swiftly than in the latter, even though there
were no difference in their velocity.

Far on beyond the shores of New Zealand the great wave coursed,
reaching at length the coast of Australia. At dawn of August 14th
Moreton Bay was visited by five well-marked waves. At Newcastle, on
the Hunter River, the sea rose and fell several times in a remarkable
manner, the oscillatory motion commencing at half-past six in the
morning. But the most significant evidence of the extent to which the
sea-wave travelled in this direction was afforded at Port Fairy,
Belfast, South Victoria. Here the oscillation of the water was
distinctly perceived at midday on August 14th; and yet, to reach this
point, the sea-wave must not only have travelled on a circuitous
course nearly equal in length to half the circumference of the earth,
but must have passed through Bass's Straits, between Australia and Van
Diemen's Land, and so have lost a considerable portion of its force
and dimensions. When wL remember that had not the effects of the
earth-shock on the water been limited by the shores of South America,
a wave of disturbance equal in extent to that which travelled westward
would have swept toward the east, we see that the force of the shock
was sufficient to have disturbed the waters of an ocean covering the
whole surface of the earth. For the sea-waves which reached Yokohama
in one direction and Port Fairy in another had each traversed a
distance nearly equal to half the earth's circumference; so that if
the surface of the earth were all sea, waves setting out in opposite
directions from the centre of disturbance would have met each other at
the antipodes of their starting-point.

It is impossible to contemplate the effects which followed the great
earthquake--the passage of a sea-wave of enormous volume over fully
one third of the earth's surface, and the force with which, on the
farthermost limits of its range, the wave rolled in upon shores more
than ten thousand miles from its starting-place--without feeling that
those geologists are right who deny that the subterranean forces of
the earth are diminishing in intensity. It may be difficult, perhaps,
to look on the effects which are ascribed to ancient earth-throes
without imagining for a while that the power of modern earthquakes is
altogether less. But when we consider fairly the share which time had
in those ancient processes of change, when we see that while mountain
ranges were being upheaved or valleys depressed to their present
position, race after race, and type after type appeared on the earth,
and lived out the long lives which belong to races and to types, we
are recalled to the remembrance of the great work which the earth's
subterranean forces are still engaged upon. Even now continents are
being slowly depressed or upheaved; even now mountain ranges are being
raised to a new level, tablelands are in process of formation, and
great valleys are being gradually scooped out. It may need an
occasional outburst, such as the earthquake of August, 1868, to remind
us that great forces are at work beneath the earth's surface. But, in
reality, the signs of change have long been noted. Old shore-lines
shift their place, old soundings vary; the sea advances in one place
and retires in another; on every side Nature's plastic hand is at work
modelling and remodelling the earth, in order that it may always be a
fit abode for those who are to dwell upon it.

[Illustration]

THE PHOSPHORESCENT SEA

(FROM STUDIES OF ANIMATED NATURE.)

BY W.S. DALLAS.

[Illustration]

It is not merely on land that this phenomenon of phosphorescence is to
be seen in living forms. Among marine animals, indeed, it is a
phenomenon much more general, much more splendid, and, we may add,
much more familiar to those who live on our coasts. There must be many
in the British Isles who have never had the opportunity of seeing the
light of the glow-worm, but there can be few of those who have
frequented in summer any part of our coasts, who have never seen that
beautiful greenish light which is then so often visible, especially on
our southern shores, when the water is disturbed by the blade of an
oar or the prow of a boat or ship. In some cases, even on our own
shores, the phenomenon is much more brilliant, every rippling wave
being crested with a line of the same peculiar light, and in warmer
seas exhibitions of this kind are much more common. It is now known
that this light is due to a minute living form, to which we will
afterward return.

But before going on to speak in some detail of the organisms to which
the phosphorescence of the sea is due, it will be as well to mention
that the kind of phosphorescence just spoken of is only one mode in
which the phenomenon is exhibited on the ocean. Though sometimes the
light is shown in continuous lines whenever the surface is disturbed,
at other times, and, according to M. de Quatrefages, more commonly,
the light appears only in minute sparks, which, however numerous,
never coalesce. "In the little channel known as the Sund de Chausez,"
he writes, "I have seen on a dark night each stroke of the oar kindle,
as it were, myriads of stars, and the wake of the craft appeared in a
manner besprinkled with diamonds." When such is the case the
phosphorescence is due to various minute animals, especially
crustaceans; that is, creatures which, microscopically small as they
are, are yet constructed more or less on the type of the lobster or
cray-fish.

At other times, again, the phosphorescence is still more partial.
"Great domes of pale gold with long streamers," to use the eloquent
words of Professor Martin Duncan, "move slowly along in endless
succession; small silvery disks swim, now enlarging and now
contracting, and here and there a green or bluish gleam marks the
course of a tiny, but rapidly rising and sinking globe. Hour after
hour the procession passes by, and the fishermen hauling in their nets
from the midst drag out liquid light, and the soft sea jellies,
crushed and torn piecemeal, shine in every clinging particle. The
night grows dark, the wind rises and is cold, and the tide changes; so
does the luminosity 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 of a
mouth leading to a short digestive cavity, and having close beside it
a filament, by means of which it probably moves about. The sphere is
filled with protoplasm, in which there is a nucleus and one or more
gaps, or "vacuoles." Such is nearly all the structure that can be
discerned with the aid of the microscope in this simple organism.

Nevertheless, this lowly form is the chief cause of that diffused
phosphorescence which is sometimes seen over a wide extent of the
ocean. How innumerable the individuals belonging to this species must
therefore be, may be left to the imagination. Probably the Noctiluca
is not rivalled in this respect even by miscroscopic unicellular algae
which compose the "red snow."

By filtering sea-water containing Noctilucae its light can be
concentrated, and it has been found that a few teaspoonfuls will then
yield light enough to enable one to read holding a book at the
ordinary distance from the eyes--about ten inches.

A singular and highly remarkable case of diffused marine
phosphorescence was observed by Nordenskioeld during his voyage to
Greenland in 1883. One dark night, when the weather was calm and the
sea smooth, his vessel was steaming across a narrow inlet called the
Igaliko Fjord, when the sea was suddenly observed to be illumined in
the rear of the vessel by a broad but sharply-defined band of light,
which had a uniform, somewhat golden sheen, quite unlike the ordinary
bluish-green phosphorescence of the sea. The latter kind of light was
distinctly visible at the same time in the wake of the vessel. Though
the steamer was going at the rate of from five to six miles an hour,
the remarkable sheet of light got nearer and nearer. When quite close,
it appeared as if the vessel were sailing in a sea of fire or molten
metal. In the course of an hour the light passed on ahead, and
ultimately it disappeared in the remote horizon. The nature of this
phenomenon Nordenskioeld is unable to explain; and unfortunately he had
not the opportunity of examining it with the spectroscope.

If we come now to consider the more partial phosphorescence of the
sea, we find that it is due to animals belonging to almost every group
of marine forms--to Echinoderms, or creatures of the sea-urchin and
star-fish type, to Annelid worm, to Medusidae, or jelly-fish, as they
are popularly called, including the "great domes" and the "silvery
disks" of the passage above quoted from Professor Martin Duncan, to
Tunicates, among which is the Pyrosoma, to Mollusks, Crustaceans, and
in very many cases to Actinozoa, or forms belonging to the type of the
sea anemone and the coral polyp.

Of these we will single out only a few for more special notice.

Many of the Medusidae, or jelly-fish, possess the character of which we
are speaking. In some cases the phosphorescence is spontaneous among
them, but in others it is not so; the creature requires to be
irritated or stimulated in some way before it will emit the light. It
is spontaneous, for example, in the _Pelagia phosphorea_, but not in
the allied _Pelagia noctiluca_, a very common form in the
Mediterranean.

In both of the jelly-fishes just mentioned the phosphorescence, when
displayed at all, is on the surface of the swimming disk, and this is
most commonly the case with the whole group. Sometimes, however, the
phosphorescence is specially localized. In some forms, as in
_Thaumantius pilosella_ and other members of the same genus, it is
seen in buds at the base of tentacles given off from the margin of the
swimming-bell. In other cases it is situated in certain internal
organs, as in the canals which radiate from the centre to the margin
of the bell, or in the ovaries. It is from this latter seat that the
phosphorescence proceeds in _Oceania pilata_, the form which gives out
such a light that Ehrenberg compared it to a lamp-globe lighted by a
flame.

The property of emitting a phosphorescent light, sometimes
spontaneously and sometimes on being stimulated, is likewise
exemplified in the Ctenophora, a group resembling the Medusidge in
the jelly-like character of their bodies, but more closely allied in
structure to the Actinozoa. But we will pass over these cases in order
to dwell more particularly on the remarkable tunicate known as
Pyrosoma, a name indicative of its phosphorescent property, being
derived from two Greek words signifying fire-body. As shown in the
illustration Pyrosoma is not a single creature, but is composed of a
whole colony of individuals, each of which is represented by one of
the projections on the surface of the tube, closed at one end, which
they all combine to form. The free end on the exterior contains the
mouth, while there is another opening in each individual toward the
interior of the tube. Such colonies, which swim about by the alternate
contraction and dilatation of the individuals composing them, are
pretty common in the Mediterranean, where they may attain the length
of perhaps fourteen inches, with a breadth of about three inches. In
the ocean they may reach a much greater size. Mr. Moseley, in his
"Notes of a Naturalist on the Challenger," mentions a giant specimen
which he once caught in the deep-sea trawl, a specimen four feet in
length and ten inches in diameter, with "walls of jelly about an inch
in thickness."

[Illustration: A. PYROSOMA. B. PONITON. (Magnified.)]

The same naturalist states that the light emitted by this compound
form is the most beautiful of all kinds of phosphorescence. When
stimulated by a touch, or shake, or swirl of the water, it "gives out
a globe of bluish light, which lasts for several seconds, as the
animal drifts past several feet beneath the surface, and then suddenly
goes out." He adds that on the giant specimen just referred to be
wrote his name with his finger as it lay on the deck in a tub at
night, and in a few seconds he had the gratification of seeing his
name come out in "letters of fire."

Among mollusks, the best known instance of phosphorescence is in the
rock-boring Pholas, the luminosity of which after death is mentioned
by Pliny. But it is not merely after death that Pholas becomes
luminous--a phenomenon perfectly familiar even in the case of many
fish, especially the herring and mackerel. It was long before the
luminosity of the living animal was known, but this is now a
well-ascertained fact; and Panceri, an Italian naturalist, recently
dead, has been able to discover in this, as in several other marine
phosphorescent forms, the precise seat of the light-giving bodies,
which he has dissected out again and again for the sake of making
experiments in connection with this subject.

A more beautiful example of a phosphorescent mollusk is presented by a
sea-slug called _Phyllirhoe bucephala_. This is a creature of from one
and a half to two inches in length, without a shell in the adult
stage, and without even gills. It breathes only by the general surface
of the body. It is common enough in the Mediterranean, but is not easy
to see, as it is almost perfectly transparent, so that it cannot be
distinguished without difficulty, by day at least, from the medium in
which it swims. By night, however, it is more easily discerned, in
consequence of its property of emitting light. When disturbed or
stimulated in any way, it exhibits a number of luminous spots of
different sizes irregularly distributed all over it, but most thickly
aggregated on the upper and under parts. These phosphorescent spots,
it is found, are not on the surface, but for the most part represent
so many large cells which form the terminations of nerves, and are
situated underneath the transparent cuticle. The spots shine with
exceptional brilliancy when the animal is withdrawn from the water and
stimulated by a drop of ammonia.

Among the Annelid worms a species of _Nereis_, or sea-centipedes, has
earned by its phosphorescent property the specific name of _noctiluca_
(night-shining), and the same property is very beautifully shown in
_Polynoe_, a near ally of the familiar sea-mouse. M. de Quatrefages
speaks with enthusiasm of the beauty of the spectacle presented by
this latter form when examined under a microscope magnifying to the
extent of a hundred diameters. He then found, as he did in the great
majority of cases which he studied, that the phosphorescence was
confined to the motor muscles, and was manifested solely when these
were in the act of contracting, manifested, too, not in continuous
lines along the course of the muscles, but in rows of brilliant
points.

More interesting than the Annelids, however, are the Alcyonarian
Actinozoa. The Actinozoa have already been described as formed on the
type of the sea-anemone and the coral polyp, that is, they are all
animals with a radiate structure, attached to one end, and having
their only opening at the other end, which is surrounded by tentacles.
In the Alcyonarian forms belonging to this great group these tentacles
are always eight in number, and fringed on both sides. Moreover, these
forms are almost without exception compound. Like the Pyrosoma, they
have a common life belonging to a whole stock or colony, as well as an
individual life.

Now, throughout this sub-division of the Actinozoa phosphorescence is
a very general phenomenon. Professor Moseley, already quoted as a
naturalist accompanying the Challenger expedition, informs us that
"all the Alcyonarians dredged by the Challenger in deep water were
found to be brilliantly phosphorescent when brought to the surface."

Among these Alcyonarians are the sea-pens mentioned in the quotation
above made from Professor Martin Duncan. Each sea-pen is a colony of
Alcyonarians, and the name is due to the singular arrangement of the
individuals upon the common stem. This stem is supported internally by
a coral rod, but its outer part is composed of fleshy matter belonging
to the whole colony. The lower portion of it is fixed in the muddy
bottom of the sea, but the upper portion is free, and gives off a
number of branches, on which the individual polyps are seated. The
whole colony thus has the appearance of a highly ornamental pen.

There is one British species, _Pennatula phosphorea_, which is found
in tolerably deep water, and is from two to four inches in length. The
specific name again indicates the phosphorescent quality belonging to
it. When irritated, it shines brilliantly, and the curious thing is
that the phosphorescence travels gradually on from polyp to polyp,
starting from the point at which the irritation is applied. If the
lower part of the stem is irritated, the phosphorescence passes
gradually upwards along each pair of branches in succession; but if
the top is irritated the phosphorescence will pass in the same way
downwards. When both top and bottom are irritated simultaneously two
luminous currents start at once, and, meeting in the middle, usually
become extinguished there; but on one occasion Panceri found that the
two crossed, and each completed its course independently of the other.
Those of our readers who have had opportunities of making or seeing
experiments with the sensitive plant (_Mimosa pudica_) will be
reminded of the way in which, when that plant is irritated, the
influence travels regularly on from pinnules to pinnules and pinnae to
pinnae.

In all the cases mentioned the phenomenon of phosphorescence is
exhibited by invertebrate animals; but though rare, it is not an
unknown phenomenon even in living vertebrates. In a genus of deep-sea
fishes called Stomias, Gunther mentions that a "series of
phosphorescent dots run along the lower side of the head, body, and
tail." Several other deep-sea fishes, locally phosphorescent, seem to
have been dredged up by the French ship Talisman in its exploring
cruise off the west coast of Northern Africa in 1883. During the same
expedition, a number of deep-sea phosphorescent crustaceans were
dredged up, the phosphorescence being in some cases diffused over the
whole body, in other cases localized to particular areas. In deep-sea
forms the phenomenon is, in fact, so common, as to have given rise to
the theory that in the depths of the ocean, where the light of the
sun cannot penetrate, the phosphorescence of various organisms diffuse
a light which limits the domain of absolute darkness.

So much by way of illustration regarding the phosphorescence exhibited
by animals, terrestrial and marine; but it ought to be noticed that
there are also a few cases in which the same phenomenon is to be
witnessed in plants. These are not so numerous as was at one time
supposed, the property having been mistakenly ascribed to some plants
not really luminous.

[Illustration: A PHOSPHORESCENT SEA.]

In some instances the mistake appears to have been due to a subjective
effect produced by brilliantly colored (red or orange) flowers, such
as the great Indian cress, the orange lily, the sunflower, and the
marigold. The fact that such flowers do give out in the dusk sudden
flashes of light has often been stated on the authority of a daughter
of Linnaeus, subsequently backed by the assertions of various other
observers. But most careful observers seem to be agreed that the
supposed flashes of light are in reality nothing else than a certain
dazzling of the eyes.

In another case, in which a moss, _Schistostega osmundacea_, has been
stated to be phosphorescent, the effect is said to be really due to
the refraction and reflection of light by minute crystals scattered
over its highly cellular leaves, and not to be produced at all where
the darkness is complete.

Among plants, genuine phosphorescence is to be found chiefly in
certain fungi, the most remarkable of which is _Rhizomorpha
subterranea_, which is sometimes to be seen ramifying over the walls
of dark, damp mines, caverns, or decayed towers, and emitting at
numerous points a mild phosphorescent light, which is sometimes bright
enough to allow of surrounding objects being distinguished by it. The
name of "vegetable glow-worm" has sometimes been applied to this
curious growth.

Among other phosphorescent fungi are several species of Agaricus,
including the _A. olearius_ of Europe, _A. Gardneri_ of Brazil, and
_A. lampas_ of Australia, and besides the members of this genus,
_Thelaphora caerulea_, which is the cause of the phosphorescent light
sometimes to be seen on decaying wood--the "touchwood" which many boys
have kept in the hope of seeing this light displayed. The milky juice
of a South American Euphorbia (_E. phosphorea_) is stated by Martins
to be phosphorescent when gently heated. But phosphorescence is
evidently not so interesting and important a phenomenon in the
vegetable as it is in the animal kingdom.

The whole phenomenon is one that gives rise to a good many questions
which it is not easy to answer, and this is especially true in the
case of animal phosphorescence. What is the nature of the light? What
are the conditions under which it is manifested? What purpose does it
serve in the animal economy?

As to the nature of the light, the principal question is whether it is
a direct consequence of the vital activity of the organism in which it
is seen, of such a nature that no further explanation can be given of
it, any more than we can explain why a muscle is contracted under the
influence of a nerve-stimulus; or whether it is due to some chemical
process more or less analogous to the burning of a candle.

The fact of luminosity appearing to be in certain cases directly under
the control of the creature in which it is found, and the fact of its
being manifested in many forms, as M. de Quatrefages found, only when
muscular contraction was taking place, would seem to favor the former
view. On the other hand, it is against this view that the
phosphorescence is often found to persist after the animal is dead,
and even in the phosphorescent organs for a considerable time after
they have been extracted from the body of the animal. In the glow-worm
the light goes on shining for some time after the death of the insect,
and even when it has become completely extinguished it can be restored
for a time by the application of a little moisture. Further, both
Matteucci and Phipson found that when the luminous substance was
extracted from the insect it would keep on glowing for thirty or forty
minutes.

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