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

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More characteristic however, are certain units of this living
sponge-colony which live in the lining membrane of the canals. In
point of fact, a sponge is a kind of Venice, a certain proportion of
whose inhabitants, like those of the famous Queen of the Adriatic
herself, live on the banks of the waterways. Just as in Venice we find
the provisions for the denizens of the city brought to the inhabitants
by the canals, so from the water, which, as we shall see, is
perpetually circulating through a sponge, the members of the
sponge-colony receive their food.

Look, again, at the sponge-fragment which lies before us. You perceive
half a dozen large holes or so, each opening on a little eminence, as
it were. These apertures, bear in mind, we call _oscula_. They are the
exits of the sponge-domain. But a close inspection of a sponge shows
that it is riddled with finer and smaller apertures. These latter are
the _pores_, and they form the entrances to the sponge-domain.

On the banks of the canal you may see growing plentifully in summer
time a green sponge, which is the common fresh-water species. Now, if
you drop a living specimen of this species into a bowl of water, and
put some powdered indigo into the water, you may note how the currents
are perpetually being swept in by the pores and out by the oscula. In
every living sponge this perpetual and unceasing circulation of water
proceeds. This is the sole evidence the unassisted sight receives of
the vitality of the sponge-colony, and the importance of this
circulation in aiding life in these depths, to be fairly carried out
cannot readily be over-estimated.

[Illustration: WHERE SPONGES GROW.]

Let us now see how this circulation is maintained. Microscopically
regarded, we see here and there, in the sides of the sponge-passages,
little chambers and recesses which remind one of the passing-places in
a narrow canal. Lining these chambers, we see living sponge-units of a
type different from the shapeless specks we noted to occur in the
meshes of the sponge substance itself. The units of the recesses each
consist of a living particle, whose free extremity is raised into a
kind of collar, from which projects a lash-like filament known as a
flagellum.

This lash is in constant movement. It waves to and fro in the water,
and the collection of lashes we see in any one chamber acts as a
veritable brush, which by its movement not only sweeps water in by the
pores, but sends it onwards through the sponge, and in due time sends
it out by the bigger holes, or oscula. This constant circulation in
the sponge discharges more than one important function. For, as
already noted, it serves the purpose of nutrition, in that the
particles on which sponge-life is supported are swept into the colony.

Again, the fresh currents of water carry with them the oxygen gas
which is a necessity of sponge existence, as of human life; while,
thirdly, waste matters, inevitably alike in sponge and in man as the
result of living, are swept out of the colony, and discharged into the
sea beyond. Our bit of sponge has thus grown from a mere dry fragment
into a living reality. It is a community in which already, low as it
is, the work of life has come to be discharged by distinct and fairly
specialized beings.

The era of new sponge-life is inaugurated by means of egg-development,
although there exists another fashion (that of gemmules or buds)
whereby out of the parental substance young sponges are produced. A
sponge-egg develops, as do all eggs, in a definite cycle. It undergoes
division (Fig. 1); its one cell becomes many; and its many cells
arrange themselves first of all into a cup-like form (5, 6 and 7),
which may remain in this shape if the sponge is a simple one, or
become developed into the more complex shape of the sponges we know.

In every museum you may see specimens of a beautiful vase-like
structure seemingly made of spun-glass. This is a flinty sponge, the
"Venus flower-basket," whose presence in the sponge family redeems it
from the charge that it contains no things of beauty whatever. So,
too, the rocks are full of fossil-sponges, many of quaint form. Our
piece of sponge, as we may understand, has yet other bits of history
attached to it.... Meanwhile, think over the sponge and its ways, and
learn from it that out of the dry things of life, science weaves many
a fairy tale.

[Illustration]

THE GREATEST SEA-WAVE EVER KNOWN

(FROM LIGHT SCIENCE IN LEISURE HOURS.)

BY R.A. PROCTOR.

[Illustration]

August 13th, 1868, one of the most terrible calamities which has ever
visited a people befell the unfortunate inhabitants of Peru. In that
land earthquakes are nearly as common as rain storms are with us; and
shocks by which whole cities are changed into a heap of ruins are by
no means infrequent. Yet even in Peru, "the land of earthquakes," as
Humboldt has termed it, no such catastrophe as that of August, 1868,
had occurred within the memory of man. It was not one city which was
laid in ruins, but a whole empire. Those who perished were counted by
tens of thousands, while the property destroyed by the earthquake was
valued at millions of pounds sterling.

Although so many months have passed since this terrible calamity took
place, scientific men have been busily engaged, until quite recently,
in endeavoring to ascertain the real significance of the various
events which were observed during and after the occurrence of the
earthquake. The geographers of Germany have taken a special interest
in interpreting the evidence afforded by this great manifestation of
Nature's powers. Two papers have been written recently on the great
earthquake of August 13th, 1868--one by Professor von Hochsteter, the
other by Herr von Tschudi, which present an interesting account of the
various effects, by land and by sea, which resulted from the
tremendous upheaving force to which the western flanks of the Peruvian
Andes were subjected on that day. The effects on land, although
surprising and terrible, only differ in degree from those which have
been observed in other earthquakes. But the progress of the great
sea-wave which was generated by the upheaval of the Peruvian shores
and propagated over the whole of the Pacific Ocean differs altogether
from any earthquake phenomena before observed. Other earthquakes have
indeed been followed by oceanic disturbances; but these have been
accompanied by terrestrial motions, so as to suggest the idea that
they had been caused by the motion of the sea-bottom or of the
neighboring land. In no instance has it ever before been known that a
well-marked wave of enormous proportions should have been propagated
over the largest ocean tract on our globe by an earth-shock whose
direct action was limited to a relatively small region, and that
region not situated in the centre, but on one side of the wide area
traversed by the wave.

We propose to give a brief sketch of the history of this enormous
sea-wave. In the first place, however, it may be well to remind the
reader of a few of the more prominent features of the great shock to
which this wave owed its origin.

It was at Arequipa, at the foot of the lofty volcanic mountain Misti,
that the most terrible effects of the great earthquake were
experienced. Within historic times Misti has poured forth no lava
streams, but that the volcano is not extinct is clearly evidenced by
the fact that in 1542 an enormous mass of dust and ashes was vomited
forth from its crater. On August 13th. 1868, Misti showed no signs of
being disturbed. So far as the volcanic neighbor was concerned, the
forty-four thousand inhabitants of Arequipa had no reason to
anticipate the catastrophe which presently befell them. At five
minutes past five an earthquake shock was experienced, which, though
severe, seems to have worked little mischief. Half a minute later,
however, a terrible noise was heard beneath the earth; a second shock
more violent than the first was felt, and then began a swaying motion,
gradually increasing in intensity. In the-course of the first minute
this motion had become so violent that the inhabitants ran in terror
out of their houses into the streets and squares. In the next two
minutes the swaying movement had so increased that the more lightly
built houses were cast to the ground, and the flying people could
scarcely keep their feet. "And now," says Von Tschudi, "there followed
during two or three minutes a terrible scene. The swaying motion which
had hitherto prevailed changed into fierce vertical upheaval. The
subterranean roaring increased in the most terrifying manner; then
were heard the heart-piercing shrieks of the wretched people, the
bursting of walls, the crashing fall of houses and churches, while
over all rolled thick clouds of a yellowish-black dust, which, had
they been poured forth many minutes longer, would have suffocated
thousands." Although the shocks had lasted but a few minutes, the whole
town was destroyed. Not one building remained uninjured, and there
were few which did not lie in shapeless heaps of ruins.

At Tacna and Arica the earth-shock was less severe, but strange and
terrible phenomena followed it. At the former place a circumstance
occurred the cause and nature of which yet remain a mystery. About
three hours after the earthquake--in other words, at about eight
o'clock in the evening--an intensely brilliant light made its
appearance above the neighboring mountains. It lasted for fully half
an hour, and has been ascribed to the eruption of some as yet unknown
volcano.

At Arica the sea-wave produced even more destructive effects than had
been caused by the earthquake. About twenty minutes after the first
earth-shock the sea was seen to retire, as if about to leave the
shores wholly dry; but presently its waters returned with tremendous
force. A mighty wave, whose length seemed immeasurable, was seen
advancing like a dark wall upon the unfortunate town, a large part of
which was overwhelmed by it. Two ships, the Peruvian corvette America,
and the United States "double-ender" Wateree, were carried nearly half
a mile to the north of Arica beyond the railroad which runs to Tacna,
and there left stranded high and dry. This enormous wave was
considered by the English vice-consul at Arica to have been fully
fifty feet in height.

At Chala three such waves swept in after the first shocks of
earthquake. They overflowed nearly the whole of the town, the sea
passing more than half a mile beyond its usual limits.

At Islay and Iquique similar phenomena were manifested. At the former
town the lava flowed in no less than five times, and each time with
greater force. Afterward the motion gradually diminished, but even an
hour and a half after the commencement of this strange disturbance the
waves still ran forty feet above the ordinary level. At Iquique the
people beheld the inrushing wave while it was still a great way off. A
dark blue mass of water some fifty feet in height was seen sweeping in
upon the town with inconceivable rapidity. An island lying before the
harbor was completely submerged by the great wave, which still came
rushing on black with the mud and slime it had swept from the
sea-bottom. Those who witnessed its progress from the upper balconies
of their houses, and presently saw its black mass rushing close
beneath their feet, looked on their safety as a miracle. Many
buildings were indeed washed away, and in the low-lying parts of the
town there was a terrible loss of life. After passing far inland, the
wave slowly returned sea-ward, and, strangely enough, the sea, which
elsewhere heaved and tossed for hours after the first great wave had
swept over it, here came soon to rest.

At Callao a yet more singular instance was afforded of the effect
which circumstances may have upon the motion of the sea after a great
earthquake has disturbed it. In former earthquakes Callao has suffered
terribly from the effects of the great sea-wave. In fact, on two
occasions the whole town has been destroyed, and nearly all its
inhabitants have been drowned, through the inrush of precisely such
waves as flowed into the ports of Arica and Chala. But upon this
occasion the centre of subterranean disturbance must have been so
situated that either the wave was diverted from Callao, or, more
probably, two waves reached Callao from different sources and at
different times, so that the two undulations partly counteracted each
other. Certain it is that, although the water retreated strangely from
the coast near Callao, insomuch that a wide tract of the sea-bottom
was uncovered, there was no inrushing wave comparable with those
described above. The sea afterward rose and fell in an irregular
manner, a circumstance confirming the supposition that the disturbance
was caused by two distinct oscillations. Six hours after the
occurrence of the earth-shock the double oscillations seemed for a
while to have worked themselves into unison, for at this time three
considerable waves rolled in upon the town. But clearly these waves
must not be compared with those which in other instances had made
their appearance within half an hour of the earth-throes. There is
little reason to doubt that if the separate oscillations had
re-enforced each other earlier, Callao would have been completely
destroyed. As it was, a considerable amount of mischief was effected;
but the motion of the sea presently became irregular again, and so
continued until the morning of August 14th, when it began to ebb with
some regularity. But during the 14th there were occasional renewals of
the irregular motion, and several days elapsed before the regular ebb
and flow of the sea were resumed.

Such were among the phenomena presented in the region where the
earthquake itself was felt. It will be seen at once that within this
region, or rather along that portion of the sea-coast which falls
within the central region of disturbance, the true character of the
sea-wave generated by the earthquake could not be recognized. If a
rock fall from a lofty cliff into a comparatively shallow sea, the
water around the place where the rock has fallen is disturbed in an
irregular manner. The sea seems at one place to leap up and down;
elsewhere one wave seems to beat against another, and the sharpest eye
can detect no law in the motion of the seething waters. But presently,
outside the scene of disturbance, a circular wave is seen to form, and
if the motion of this wave be watched it is seen to present the most
striking contrast with the turmoil and confusion at its centre. It
sweeps onward and outward in a regular undulation. Gradually it loses
its circular figure (unless the sea-bottom happens to be unusually
level), showing that although its motion is everywhere regular, it is
not everywhere equally swift. A wave of this sort, though incomparably
vaster, swept swiftly away on every side from the scene of the great
earthquake near the Peruvian Andes. It has been calculated that the
width of this wave varied from one million to five million feet, or,
roughly, from two hundred to one thousand miles, while, when in
mid-Pacific, the length of the wave, measured along its summit in a
widely-curved path from one side to another of the great ocean,
cannot have been less than eight thousand miles.

[Illustration: OVER A LARGE PORTION OF ITS COURSE ITS PASSAGE WAS
UNNOTED.]

We cannot tell how deep-seated was the centre of subterranean action;
but there can be no doubt it was very deep indeed, because otherwise
the shock felt in towns separated from each other by hundreds of miles
could not have been so nearly contemporaneous. Therefore the portion
of the earth's crust upheaved must have been enormous, for the length
of the region where the direct effects of the earthquake were
perceived is estimated by Professor von Hochsteter at no less than
two hundred and forty miles. The breadth of the region is unknown,
because the slope of the Andes on one side and the ocean on the other
concealed the motion of the earth's crust.

The great ocean-wave swept, as we have said, in all directions around
the scene of the earth-throe. Over a large part of its course its
passage was unnoted, because in the open sea the effects even of so
vast an undulation could not be perceived. A ship would slowly rise as
the crest of the great wave passed under her, and then as slowly sink
again. This may seem strange, at first sight, when it is remembered
that in reality the great sea-wave we are considering swept at the
rate of three or four hundred sea-miles an hour over the larger part
of the Pacific. But when the true character of ocean-waves is
understood, when it is remembered that there is no transference of the
water itself at this enormous rate, but simply a transmission of
motion (precisely as when in a high wind waves sweep rapidly over a
cornfield, while yet each cornstalk remains fixed in the ground), it
will be seen that the effects of the great sea-wave could only be
perceived near the shore. Even there, as we shall presently see, there
was much to convey the impression that the land itself was rising and
falling rather than that the deep was moved. But among the hundreds of
ships which were sailing upon the Pacific when its length and breadth
were traversed by the great sea-wave, there was not one in which any
unusual motion was perceived.

In somewhat less than three hours after the occurrence of the
earthquake the ocean-wave inundated the port of Coquimbo, on the
Chilean seaboard, some eight hundred miles from Arica. An hour or so
later it had reached Constitucion, four hundred and fifty miles
farther south; and here for some three hours the sea rose and fell
with strange violence. Farther south, along the shore of Chile, even
to the island of Chiloe, the shore-wave travelled, though with
continually diminishing force, owing, doubtless, to the resistance
which the irregularities of the shore opposed to its progress.

The northerly shore-wave seems to have been more considerable; and a
moment's study of a chart of the two Americas will show that this
circumstance is highly significant. When we remember that the
principal effects of the land-shock were experienced within that angle
which the Peruvian Andes form with the long north-and-south line of
the Chilean and Bolivian Andes, we see at once that, had the centre of
the subterranean action been near the scene where the most destructive
effects were perceived, no sea-wave, or but a small one, could have
been sent toward the shores of North America. The projecting shores of
northern Peru and Ecuador could not have failed to divert the sea-wave
toward the west; and though a reflected wave might have reached
California, it would only have been after a considerable interval of
time, and with dimensions much less than those of the sea-wave which
travelled southward. When we see that, on the contrary, a wave of even
greater proportions travelled toward the shores of North America, we
seem forced to the conclusion that the centre of the subterranean
action must have been so far to the west that the sea-wave generated
by it had a free course to the shores of California.

Be this as it may, there can be no doubt that the wave which swept the
shores of Southern California, rising upward of sixty feet above the
ordinary sea-level, was absolutely the most imposing of all the
indirect effects of the great earthquake. When we consider that even
in San Pedro Bay, fully five thousand miles from the centre of
disturbance, a wave twice the height of an ordinary house rolled in
with unspeakable violence only a few hours after the occurrence of the
earth-throe, we are most strikingly impressed with the tremendous
energy of the earth's movement.

Turning to the open ocean, let us track the great wave on its course
past the multitudinous islands which dot the surface of the Pacific.

The inhabitants of the Sandwich Islands, which lie about six thousand
three hundred miles from Arica, might have imagined themselves safe
from any effects which could be produced by an earthquake taking place
so far away from them. But on the night between August 13th and 14th,
the sea around this island group rose in a surprising manner, insomuch
that many thought the islands were sinking, and would shortly subside
altogether beneath the waves. Some of the smaller islands, indeed,
were for a time completely submerged. Before long, however, the sea
fell again, and as it did so the observers "found it impossible to
resist the impression that the islands were rising bodily out of the
water." For no less than three days this strange oscillation of the
sea continued to be experienced, the most remarkable ebbs and floods
being noticed at Honolulu, on the island of Woahoo.

But the sea-wave swept onward far beyond these islands.

At Yokohama, in Japan, more than ten thousand five hundred miles from
Arica, an enormous wave poured in on August 14th, but at what hour we
have no satisfactory record. So far as distance is concerned, this
wave affords most surprising evidence of the stupendous nature of the
disturbance to which the waters of the Pacific Ocean had been
subjected. The whole circumference of the earth is but twenty-five
thousand miles, so that this wave had travelled over a distance
considerably greater than two-fifths of the earth's circumference. A
distance which the swiftest of our ships could not traverse in less
than six or seven weeks had been swept over by this enormous
undulation in the course of a few hours.

More complete details reach us from the Southern Pacific.

Shortly before midnight the Marquesas Isles and the low-lying Tuamotu
group were visited by the great wave, and some of these islands were
completely submerged by it. The lonely Opara Isle, where the steamers
which run between Panama and New Zealand have their coaling station,
was visited at about half-past eleven in the evening by a billow which
swept away a portion of the coal depot. Afterward great waves came
rolling in at intervals of about twenty minutes, and several days
elapsed before the sea resumed its ordinary ebb and flow.

It was not until about half-past two on the morning of August 14th
that the Samoa Isles (sometimes called the Navigator Islands) were
visited by the great wave. The watchmen startled the inhabitants from
their sleep by the cry that the sea was about to overwhelm them; and
already, when the terrified people rushed from their houses, the sea
was found to have risen far above the highest water-mark. But it
presently began to sink again, and then commenced a series of
oscillations, which lasted for several days, and were of a very
remarkable nature. Once in every quarter of an hour the sea rose and
fell, but it was noticed that it rose twice as rapidly as it sank.
This peculiarity is well worth remarking. The eminent physicist Mallet
speaks thus (we follow Lyell's quotation) about the waves which
traverse an open sea: "The great sea-wave, advancing at the rate of
several miles in a minute, consists, in the deep ocean, of a long, low
swell of enormous volume, having an equal slope before and behind, and
that so gentle that it might pass under a ship without being noticed.
But when it reaches the edge of soundings, its front slope becomes
short and steep, while its rear slope is long and gentle." On the
shores visited by such a wave, the sea would appear to rise more
rapidly than it sank. We have seen that this happened on the shores of
the Samoa group, and therefore the way in which the sea rose and fell
on the days following the great earthquake gave significant evidence
of the nature of the sea-bottom in the neighborhood of these islands.
As the change of the great wave's figure could not have been quickly
communicated, we may conclude with certainty that the Samoan Islands
are the summits of lofty mountains, whose sloping sides extend far
toward the east.

This conclusion affords interesting evidence of the necessity of
observing even the seemingly trifling details of important phenomena.

The wave which visited the New Zealand Isles was altogether different
in character, affording a noteworthy illustration of another remark of
Mallet's. He says that where the sea-bottom slopes in such a way that
there is water of some depth close inshore, the great wave may roll in
and do little damage; and we have seen that so it happened in the case
of the Samoan Islands. But he adds that, "where the shore is shelving
there will be first a retreat of the water, and then the wave will
break upon the beach and roll far in upon the land." This is precisely
what happened when the great wave reached the eastern shores of New
Zealand, which are known to shelve down to very shallow water,
continuing far away to sea toward the east.

At about half-past three on the morning of August 14th the water began
to retreat in a singular manner from the port of Littleton, on the
eastern shores of the southernmost of the New Zealand Islands. At
length the whole port was left entirely dry, and so remained for about
twenty minutes. Then the water was seen returning like a wall of foam
ten or twelve feet in height, which rushed with a tremendous noise
upon the port and town. Toward five o'clock the water again retired,
very slowly as before, not reaching its lowest ebb until six. An hour
later a second huge wave inundated the port. Four times the sea
retired and returned with great power at intervals of about two hours.
Afterward the oscillation of the water was less considerable, but it
had not wholly ceased until August 17th, and only on the 18th did the
regular ebb and flow of the tide recommence.

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