Part 9 (1/2)
CHAPTER FOURTEEN.
ANIMAL LIFE IN THE SEA--MEDUSAE--FOOD OF THE WHALE--PHOSPHORIC LIGHT-- CAUSE THEREOF--LUMINOSITY OF THE OCEAN.
Reference has elsewhere been made in this volume to the immense amount of animal life that exists in the ocean, not only in the form of fish of all sizes, but in that of animalcules, which, although scarcely visible to the naked eye, are, in some cases, so innumerable as to give a distinct colouring to the water.
The _Medusae_, or, more familiarly, sea blubbers, are seen in the waters that lave our own sh.o.r.es. They are of various sizes, from that of a large plate to a pin-head. They are almost colourless, like clear jelly, and when carelessly observed, seem to be dead objects drifting with the tide; but a closer observation shows that they are possessed of life, though not of a particularly active kind, and that they swim by alternate contractions and expansions of their bodies. These creatures const.i.tute a large part of the whale's food. Some of them are flat, some semi-globular, others are bell-shaped, while some have got little heads and small fins. Of these last it is said that each little creature has no fewer than three hundred and sixty thousand minute suckers on its head with which it seizes its prey. When we think of the exceeding smallness of the creatures thus preyed upon, and consider the fact that each little thing must obtain food by making war upon some creatures still smaller than itself, we are led almost in spite of ourselves into that mysteriously metaphysical question--infinitesimal _divisibility_; which may be translated thus--the endless division and subdivision of atoms. This subject has puzzled the heads of the profoundest philosophers of all ages; we will not, therefore, puzzle our readers with it any further.
Scoresby tells us that the colour of the Greenland Sea varies from ultramarine blue to olive-green, from the purest transparency to striking opacity; and that these colours are permanent, and do not depend on the state of the weather, but on the quality of the water. He observed that whales were found in much greater numbers in the green than in the blue water; and he found, on examining the former with the microscope, that its opacity and its colour were due to countless mult.i.tudes of those animalcules on which the whale feeds.
We need scarcely remark that it is utterly beyond the power of man to form anything approaching to a correct conception of the amount of _life_ that is thus shown to exist in the ocean. Although it has pleased the Creator to limit our powers, yet it has also pleased him to leave the limit of those powers undefined. We may not, indeed, ever hope in this life to attain to perfect knowledge, nevertheless, by ”searching” we may ”find out wisdom;” and certain it is, that, although there undoubtedly must be a point of knowledge on any given subject which man cannot reach, there is in man a power incessantly to extend his knowledge and increase his powers of conception, by each successive effort that he makes in his course from the cradle to the grave.
Even although we were told the exact number of the little creatures that inhabit the sea, we could not, by any simple effort of the mind, however powerful, form a conception of what that number implied. We might shut ourselves up like the hermits of old, abstract our thoughts from all other things, and ponder the subject for weeks or months together, and at the termination of our effort we should be as wise as we were at its commencement, but no wiser. But by searching round the subject, and comparing lesser things with greater, although we should still fail to arrive at a full comprehension of the truth, we may advance our powers of conception very considerably beyond the point attained by our first effort; and which point, as we have said, could not be surmounted by a hair's breadth by the mere exertion of simple or abstract thought.
Dr Scoresby's remarks on the subject of animal life in the ocean, are so graphic and curious that we extract the pa.s.sages verbatim from the admirable memoir of that gentleman, written by his nephew. He says:
”I procured a quant.i.ty of snow from a piece of ice that had been washed by the sea, and was greatly discoloured by the decomposition of some peculiar substance upon it. A little of this snow dissolved in a wine-gla.s.s appeared perfectly nebulous--the water being found to contain a great number of semi-transparent spherical substances, with others resembling small portions of fine hair. On examining these substances with a compound microscope, I was enabled to make the following observations:--
”The semi-transparent globules appeared to consist of an animal of the medusa kind. It was from one-twentieth to one-thirtieth of an inch in diameter. Its surface was marked with twelve distinct patches, or nebulae, of dots of a brownish colour. These dots were disposed in pairs, four pairs or sixteen pairs alternately, composing one of the nebula. The body of the medusa was transparent. When the water containing these animals was heated, it emitted a very strong odour, in some respects resembling the smell of oysters when thrown on hot coals, but much more offensive.
”The fibrous or hair-like substances were more easily examined, being of a darker colour. They varied in length from a point to one-tenth of an inch; and when highly magnified, were found beautifully moniliform.
Whether they were living animals, and possessed of locomotion, I could not ascertain. They possessed the property of decomposing light, and in some cases showed all the colours of the spectrum very distinctly.
”I afterwards examined the different qualities of sea water, and found these substances very abundant in that of an olive-green colour; and also occurring, but in lesser quant.i.ty, in the bluish-green water. The number of medusae in the olive-green water was found to be immense.
They were about one-fourth of an inch asunder. In this proportion, a cubic inch of water must contain 64; a cubic foot 110,592; a cubic fathom 23,887,872; and a cubic mile about 23,888,000,000,000,000.”
Of course we have, in the last two numbers, reached the utterly incomprehensible; but Dr Scoresby goes into comparisons which help us a little, at least to ascertain how hopelessly beyond our conceptions such numbers are.
”From soundings made in the situation where these animals were found, it is probable the sea is upwards of a mile in depth; but whether these substances occupy the whole depth is uncertain. Provided, however, the depth to which they extend be but two hundred and fifty fathoms, the above immense number of one species may occur in the s.p.a.ce of two miles square. It may give a better conception of the amount of medusae in this extent, if we calculate the length of time that would be requisite, with a certain number of persons, for counting this number. Allowing that one person could count a million in seven days, which is barely possible, it would have required that eighty thousand persons should have started at the creation of the world to complete the enumeration at the present time!
”What a stupendous idea this gives of the immensity of creation, and of the bounty of Divine Providence in furnis.h.i.+ng such a profusion of life in a region so remote from the habitations of men!
”The larger portion of these medusae, consisting of transparent substances of a lemon-yellow colour, and globular form, appeared to possess very little power of motion. Some of them were seen advancing by a slight waving motion, at the rate of a hundred and eightieth of an inch in a second; and others, spinning round with considerable celerity, gave great interest and liveliness to the examination. But the progressive motion of the most active, however distinct and rapid it might appear under a high magnifying power, was, in reality, extremely slow; for it did not exceed an inch in three minutes. At this rate they would require one hundred and fifty-one days to travel a nautical mile.
”The vastness of their numbers, and their exceeding minuteness, are circ.u.mstances, discovered in the examination of these animalcules, of uncommon interest. In a drop of water examined by a power of 28.224 (magnified superficies) there were fifty in number, on an average, in each square of the micrometer gla.s.s, of an eight hundred and fortieth of an inch; and as the drop occupied a circle on a plate of gla.s.s containing 529 of these squares, there must have been, in this single drop of water, taken out of the yellowish-green sea, in a place by no means the most discoloured, about 26,450 animalcules. Hence, reckoning sixty drops to a dram, there would be a number in a gallon of water exceeding, by one half the amount of the population of the whole globe!
It gives a powerful conception of the minuteness and wonders of creation, when we think of more than twenty-six thousand animals living, obtaining subsistence, and moving perfectly at their ease, without annoyance to one another, in a single drop of water... A whale requires a sea, an ocean, to sport in. About one hundred and fifty millions of these animalcules would have abundant room in a tumbler of water!”
But besides furnis.h.i.+ng food to the whale, and, no doubt, to many other of the inhabitants of the deep, those medusae are the cause of the phosph.o.r.escent light that sometimes glows on the ocean with resplendent brilliancy. We see this light oftentimes on our own coasts. It is usually of a pale bluish-white colour, more or less intense, apparently, according to the condition of the creatures by which it is emitted. It can only be seen at night. We have seen it on the west coast of Scotland, so bright that the steamer in which we sailed left behind her what appeared to be a broad highway of liquid fire.
At times it requires vigorous motion, such as takes place when an oar is dipped, a stone thrown, or paddle-wheels dashed into the water; but at other times, the mere motion of the ocean swell, even in calm weather, is sufficient to stir up the lambent light and cause the crest of every undulation to glitter as if tipped with burnished silver. In such circ.u.mstances we have seen the ends of the oars of a boat silvered with it when lifted out of the wave, and the drops which fell from them before being redipped resembled the most beautiful diamonds.
Mr P.H. Gosse, in his interesting work, ”The Ocean,” gives the following account of this luminosity of the sea, as witnessed by himself on one occasion:
”In a voyage to the Gulf of Mexico, I saw the water in those seas more splendidly luminous than I had ever observed before. It was indeed a magnificent sight, to stand on the fore-part of the vessel and watch her breasting the waves. The ma.s.s of water rolled from her bows as white as milk, studded with those innumerable sparkles of blue light. The nebulosity instantly separated into small ma.s.ses, curdled like clouds of marbles, leaving the water between of its own clear blackness; the clouds soon subsided, but the sparks remained. Sometimes one of these points, of greater size and brilliancy than the rest, suddenly burst into a small cloud of superior whiteness to the ma.s.s, and be then lost in it. The curdling of the milky appearance into clouds and ma.s.ses, and its quick subsidence, were what I had never before observed elsewhere.”
Many scientific travellers have carefully examined this subject, and we believe that all agree in referring this beautiful appearance to the medusae. One gentleman drew a bucketful of water from the sea when it was in this condition, and found, on examining it in a dark place, that the little creatures ”could be distinctly seen emitting a bright speck of light. Sometimes this was like a sudden flash, at others appearing like an oblong or round luminous point, which continued bright for a short time, like a lamp lit beneath the water and moving through it, still possessing its definite shape, and then suddenly disappearing.
When the bucket was sharply struck on the outside, there would appear at once a great number of these luminous bodies, which retained their brilliant appearance for a few seconds, and then all was dark again.
They evidently appeared to have it under their own will, giving out their light frequently, at various depths in the water, without any agitation being given to the bucket. At times might be seen minute but pretty bright specks of light, darting across a piece of water and then vanis.h.i.+ng; the motion of the light being exactly that of the cyclops through the water. Upon removing a tumblerful from the bucket, and taking it to the light, a number of cyclops were accordingly found swimming and darting about in it.”