Chapter VII: Front Matter (7)

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.

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.

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 we 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.

THE PHOSPHORESCENT SEA

(FROM STUDIES OF ANIMATED NATURE.)

BY W.S. DALLAS.

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 algæ which compose the "red snow."

By filtering sea-water containing Noctilucæ 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 Nordenskiöld 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 Nordenskiöld 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 Medusidæ, 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 Medusidæ, 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 Medusidæ 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."

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 _Phyllirhoë 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 _Polynoë_, 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.

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 Linnæus, 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 cærulea_, 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.

In Pholas the light is still more persistent, and it is found that when the dead body of this mollusk is placed in honey, it will retain for more than a year the power of emitting light when plunged in warm water.

The investigations of recent years have rendered it more and more probable that the light exhibited by phosphorescent organisms is due to a chemical process somewhat analogous to that which goes on in the burning of a candle. This latter process is one of rapid oxidation. The particles of carbon supplied by the oily matter that feeds the candle become so rapidly combined with oxygen derived from the air that a considerable amount of light, along with heat, is produced thereby. Now, the phenomenon of phosphorescence in organic forms, whether living or dead, appears also to be due to a process of oxidation, but one that goes on much more slowly than in the case of a lighted candle. It is thus more closely analogous to what is observed in the element phosphorus itself, which owes its name (meaning "light-bearer") to the fact that when exposed to the air at ordinary temperatures it glows in the dark, in consequence of its becoming slowly combined with oxygen.

At one time it was believed that the presence of oxygen was not necessary to the exhibition of phosphorescence in organic forms, but it has now been placed beyond doubt that this is a mistake. Oxygen has been proved to be indispensable, and hence we see a reason for the luminous organs in the glow-worm being so intimately connected, as above mentioned, with the air-tubes that ramify through the insect.

This fact of itself might be taken as a strong indication of the chemical nature of the process to which phosphorescence is due. But the problem has been made the subject of further investigations which have thrown more light upon it. It was long known that there were various inorganic bodies besides phosphorus which emitted a phosphorescent light in the dark, at least after being exposed to the rays of the sun; but it was not till quite recently that any organic compound was known to phosphoresce at ordinary temperatures.

This discovery was made by a Polish chemist, named Bronislaus Radziszewski, who followed it up with a long series of experiments on the phosphorescence of organic compounds, by which he was able to determine the conditions under which that phenomenon was exhibited. In all the substances investigated by him in which phosphorescence was introduced he found that three conditions were essential to its production: (1) that oxygen should be present; (2) that there should be an alkaline reaction in the phosphorescing mixture--that is, a reaction such as is produced on acids and vegetable coloring matters by potash, soda, and the other alkalies; and (3) that some kind of chemical action should take place.

He found, moreover, that among the organic compounds that could be made to phosphoresce under these conditions were nearly all the fixed and ethereal oils. With reference to the phosphorescence of animals, this observation is important, for it has been shown in a great many cases that a fatty substance forms the main constituent in their luminous organs. This has long been known to be the case in the luminous insects belonging to the Lampyridæ and Elateridæ, as well as in the luminous centipedes; and the researches of Panceri, already referred to, on the luminous organs of many marine forms have shown that it holds good with regard to these also.

We may, therefore, conclude that substances fitted to phosphoresce under the conditions determined by the experiments of Radziszewski are generally, and probably universally, present in the luminous organs of phosphorescent animals. Now, what is to be said as to the occurrence of these conditions? The access of oxygen is in all cases easy to account for, but it must also be shown how the alkaline reaction is to be produced. We need not expect to find in animal organisms potash, soda, ammonia, and the other common alkalies; but it was established by experiment that the alkaline organic compounds cholin and neurin, which are present in animal tissues, would also serve to bring about the phenomenon of phosphorescence in the substances on which the experiments were made.

Accordingly, it seems fair to conclude that when all these conditions for the production of phosphorescence in a chemical laboratory are present in animal organisms, the phenomenon, when observed in these, is exactly of the same nature as that which is produced artificially. By that it is meant that animal phosphorescence is attended, like the artificial phenomenon, by a slow chemical action, or in other words, that the phosphorescent light is due to a gradual process of oxidation.

One curious circumstance has been discovered which lends still further probability to this explanation. It was mentioned above that among phosphorescent plants there are several species of Agaricus. Now, from one species of this genus, though not indeed one of the phosphorescent species (from _A. muscarius_) there has been extracted a principle called _amanitia_, which is found to be identical with cholin. In the light of the results derived from the investigations just referred to it is reasonable to draw the conclusion that, if sought for, this principle would likewise be found in the phosphorescent species in which the other conditions of phosphorescence are also present.

On this theory of the production of the phenomenon now under consideration, the effect of shaking or of vital action in giving rise to or intensifying the exhibition of the light is accounted for by the fact that by these means fresh supplies of oxygen are brought into contact with the phosphorescent substance. The effect of ammonia on the light emitted by the sea-slug _Phyllirhoë bucephala_, is also fully explained, ammonia being one of those alkaline substances which are so directly favorable to the exhibition of the phenomenon.

Nor is it difficult to account for the control which in some cases insects appear to have over the luminosity of the phosphorescent organs, exhibiting and withdrawing the light at will. It is not necessary to suppose that this is an immediate effect, a conversion of nerve force into light, and a withdrawal of that force. The action of the creature's will may be merely in maintaining or destroying the conditions under which the light is manifested. It may, for example, have the power of withdrawing the supply of oxygen, and this supposition receives some countenance from the observation cited from Kirby and Spence on the two captured glow-worms, one of which withdrew its light, while the other kept it shining, but while doing so had the posterior extremity of the abdomen in constant motion. But the animal may also have the power in another way of affecting the chemical conditions of the phenomenon. It may, for example, have the power of increasing or diminishing by some nervous influence the supply of the necessary alkaline ingredient.

But if animal phosphorescence is really due to a process of slow oxidation, there is one singular circumstance to be noted in connection with it. Oxidation is a process that is normally accompanied by the development of heat. Even where no light is produced an increase of temperature regularly takes place when substances are oxidized. We ought, then, to expect such a rise of temperature when light is emitted by the phosphorescent organs of animals. But the most careful observations have shown that nothing of the kind can be detected. It was with a view to test this that Panceri dissected out the luminous organs of so many specimens of Pholas. He selected this mollusk because it was so abundant in the neighborhood of Naples, where, his experiments were made; and in making his experiments he made use of a thermopile, an apparatus by which, with the aid of electricity, much smaller quantities of heat can be indicated than by means of the most delicate thermometer. The organs remained luminous long after they were extracted, but no rise in temperature whatever could be found to accompany the luminosity. Many experiments upon different animals were made with similar negative results by means of the thermometer.

The only explanation of this that can be given is probably to be found in the fact that the chemical process ascertained to go on in the phosphorescence of organic compounds on which experiments were made in the laboratory is an extremely slow one.