The Botanic Garden Volume I Part 28

_You round Echinus ray his arrowy mail, Give the keel'd Nautilus his oar and sail.

Firm to his rock with silver cords suspend The anch.o.r.ed Pinna, and his Cancer-friend_.

CANTO III. l. 67.

The armour of the Echinus, or Sea-hedge Hog, consists generally of moveable spines; (_Linnei System. Nat._ Vol. I. p. 1102.) and in that respect resembles the armour of the land animal of the same name. The irregular protuberances on other sea-sh.e.l.ls, as on some species of the Purpura, and Murex, serve them as a fortification against the attacks of their enemies.

It is said that this animal foresees tempestuous weather, and sinking to the bottom of the sea adheres firmly to sea-plants, or other bodies by means of a substance which resembles the horns of snails. Above twelve hundred of these fillets have been counted by which this animal fixes itself; and when afloat, it contracts these fillets between the bases of its points, the number of which often amounts to two thousand. Dict raisonne. art. Oursin. de mer.

There is a kind of Nautilus, called by Linneus, Argonauta, whose sh.e.l.l has but one cell; of this animal Pliny affirms, that having exonerated its sh.e.l.l by throwing out the water, it swims upon the surface, extending a web of wonderful tenuity, and bending back two of its arms and rowing with the rest, makes a sail, and at length receiving the water dives again. Plin. IX. 29. Linneus adds to his description of this animal, that like the Crab Diogenes or Bernhard, it occupies a house not its own, as it is not connected to its sh.e.l.l, and is therefore foreign to it; who could have given credit to this if it had not been attested by so many who have with their own eyes seen this argonaut in the act of sailing? Syst. Nat p. 1161.

The Nautilus, properly so named by Linneus, has a sh.e.l.l consisting of many chambers, of which cups are made in the East with beautiful painting and carving on the mother-pearl. The animal is said to inhabit only the uppermost or open chamber, which is larger than the rest; and that the rest remain empty except that the pipe, or siphunculus, which communicates from one to the other of them is filled with an appendage of the animal like a gut or string. Mr. Hook in his Philos. Exper. p.

306, imagines this to be a dilatable or compressible tube, like the air- bladders of fish, and that by contracting or permitting it to expand, it renders its sh.e.l.l boyant or the contrary. See Note on Ulva, Vol. II.

The Pinna, or Sea-wing, is contained in a two-valve sh.e.l.l, weighing sometimes fifteen pounds, and emits a beard of fine long glossy silk- like fibres, by which it is suspended to the rocks twenty or thirty feet beneath the surface of the sea. In this situation it is so successfully attacked by the eight-footed Polypus, that the species perhaps could not exist but for the exertions of the Cancer Pinnotheris, who lives in the same sh.e.l.l as a guard and companion. Amoen. Academ. Vol. II. p. 48. Lin.

Syst. Nat. Vol. I. p. 1159, and p. 1040.

The Pinnotheris, or Pinnophylax, is a small crab naked like Bernard the Hermit, but is furnished with good eyes, and lives in the same sh.e.l.l with the Pinna; when they want food the Pinna opens its sh.e.l.l, and sends its faithful ally to forage; but if the Cancer sees the Polypus, he returns suddenly to the arms of his blind hostess, who by closing the sh.e.l.l avoids the fury of her enemy; otherwise, when it has procured a booty, it brings it to the opening of the sh.e.l.l, where it is admitted, and they divide the prey. This was observed by Haslequist in his voyage to Palestine.

The Byssus of the antients, according to Aristotle, was the beard of the Pinna above mentioned, but seems to have been used by other writers indiscriminately for any spun material, which was esteemed finer or more valuable than wool. Reaumur says the threads of this Byssus are not less fine or less beautiful than the silk, as it is spun by the silk-worm; the Pinna on the coasts of Italy and Provence (where it is fished up by iron-hooks fixed on long poles) is called the silk-worm of the sea. The stockings and gloves manufactured from it, are of exquisite fineness, but too warm for common wear, and are thence esteemed useful in rhumatism and gout. Dict. raisonne art. Pinne-marine. The warmth of the Byssus, like that of silk, is probably owing to their being bad conductors of heat, as well as of electricity. When these fibres are broken by violence, this animal as well as the muscle has the power to reproduce them like the common spiders, as was observed by M. Adanson.

As raw silk, and raw cobwebs, when swallowed, are liable to produce great sickness (as I am informed) it is probable the part of muscles, which sometimes disagrees with the people who eat them, may be this silky web, by which they attach themselves to stones. The large kind of Pinna contains some mother-pearl of a reddish tinge, according to M.

d'Argenville. The substance sold under the name of Indian weed, and used at the bottom of fish-lines, is probably a production of this kind; which however is scarcely to be distinguished by the eye from the tendons of a rat's tail, after they have been separated by putrefaction in water, and well cleaned and rubbed; a production, which I was once shewn as a great curiosity; it had the uppermost bone of the tail adhering to it, and was said to have been used as an ornament in a lady's hair.

NOTE XXVIII.--STURGEON.

_With worm-like hard his toothless lips array, And teach the unweildy Sturgeon to betray._

CANTO III. l. 71.

The Sturgeon, _Acipenser, Strurio._ Lin. Syst. Nat. Vol. I. p. 403. is a fish of great curiosity as well as of great importance; his mouth is placed under the head, without teeth, like the opening of a purse, which he has the power to push suddenly out or retract. Before this mouth under the beak or nose hang four tendrils some inches long, and which so resemble earth-worms that at first sight they may be mistaken for them.

This clumsy toothless fish is supposed by this contrivance to keep himself in good condition, the solidity of his flesh evidently shewing him to be a fish of prey. He is said to hide his large body amongst the weeds near the sea-coast, or at the mouths of large rivers, only exposing his cirrhi or tendrils, which small fish or sea-insects mistaking for real worms approach for plunder, and are sucked into the jaws of their enemy. He has been supposed by some to root into the soil at the bottom of the sea or rivers; but the cirrhi, or tendrills abovementioned, which hang from his snout over his mouth, must themselves be very inconvenient for this purpose, and as it has no jaws it evidently lives by suction, and during its residence in the sea a quant.i.ty of sea-insects are found in its stomach.

The flesh was so valued in the time of the Emperor Severus, that it was brought to table by servants with coronets on their heads, and preceded by music, which might give rise to its being in our country presented by the Lord Mayor to the King. At present it is caught in the Danube, and the Walga, the Don, and other large rivers for various purposes. The skin makes the best covering for carriages; isingla.s.s is prepared from parts of the skin; cavear from the sp.a.w.n; and the flesh is pickled or salted, and sent all over Europe.

NOTE XXIX.--OIL ON WATER.

_Who with fine films, suspended o'er the deep, Of Oil effusive lull the waves to sleep._

CANTO III. l. 87.

There is reason to believe that when oil is poured upon water, the two surfaces do not touch each other, but that the oil is suspended over the water by their mutual repulsion. This seems to be rendered probable by the following experiment: if one drop of oil be droped on a bason of water, it will immediately diffuse itself over the whole, for there being no friction between the two surfaces, there is nothing to prevent its spreading itself by the gravity of the upper part of it, except its own tenacity, into a pellicle of the greatest tenuity. But if a second drop of oil be put upon the former, it does not spread itself, but remains in the form of a drop, as the other already occupied the whole surface of the bason, and there is friction in oil pa.s.sing over oil, though none in oil pa.s.sing over water.

Hence when oil is diffused on the surface of water gentle breezes have no influence in raising waves upon it; for a small quant.i.ty of oil will cover a very great surface of water, (I suppose a spoonful will diffuse itself over some acres) and the wind blowing upon this carries it gradually forwards; and there being no friction between the two surfaces the water is not affected. On which account oil has no effect in stilling the agitation of the water after the wind ceases, as was found by the experiments of Dr. Franklin.

This circ.u.mstance lately brought into notice by Dr. Franklin had been mentioned by Pliny, and is said to be in use by the divers for pearls, who in windy weather take down with them a little oil in their mouths, which they occasionally give out when the inequality of the supernatant waves prevents them from seeing sufficiently distinctly for their purpose.

The wonderful tenuity with which oil can be spread upon water is evinced by a few drops projected from a bridge, where the eye is properly placed over it, pa.s.sing through all the prismatic colours as it diffuses itself. And also from another curious experiment of Dr. Franklin's: he cut a piece of cork to about the size of a letter-wafer, leaving a point standing off like a tangent at one edge of the circle. This piece of cork was then dipped in oil and thrown into a large pond of water, and as the oil flowed off at the point, the cork-wafer continued to revolve in a contrary direction for several minutes. The oil flowing off all that time at the pointed tangent in coloured streams. In a small pond of water this experiment does not so well succeed, as the circulation of the cork stops as soon as the water becomes covered with the pellicle of oil. See Additional Note, No. XIII. and Note on Fucus, Vol. II.

The ease with which oil and water slide over each other is agreeably seen if a phial be about half filled with equal parts of oil and water, and made to oscillate suspended by a string, the upper surface of the oil and the lower one of the water will always keep smooth; but the agitation of the surfaces where the oil and water meet, is curious; for their specific gravities being not very different, and their friction on each other nothing, the highest side of the water, as the phial descends in its oscillation, having acquired a greater momentum than the lowest side (from its having descended further) would rise the highest on the ascending side of the oscillation, and thence pushes the then uppermost part of the water amongst the oil.

NOTE x.x.x.--SHIP-WORM.

_Meet fell Teredo, as he mines the keel With beaked head, and break his lips of steel._

CANTO III. l. 91.

The Teredo, or ship-worm, has two calcareous jaws, hemispherical, flat before, and angular behind. The sh.e.l.l is taper, winding, penetrating ships and submarine wood, and was brought from India into Europe, Linnei System. Nat. p. 1267. The Tarieres, or sea-worms, attack and erode ships with such fury, and in such numbers, as often greatly to endanger them.

It is said that our vessels have not known this new enemy above fifty years, that they were brought from the sea about the Antilles to our parts of the ocean, where they have increased prodigiously. They bore their pa.s.sage in the direction of the fibres of the wood, which is their nourishment, and cannot return or pa.s.s obliquely, and thence when they come to a knot in the wood, or when two of them meet together with their stony mouths, they perish for want of food.

In the years 1731 and 1732 the United Provinces were under a dreadful alarm concerning these insects, which had made great depredation on the piles which support the banks of Zeland, but it was happily discovered a few years afterwards that these insects had totally abandoned that island, (Dict Raisonne, art, Vers Rongeurs,) which might have been occasioned by their not being able to live in that lat.i.tude when the winter was rather severer than usual.

NOTE x.x.xI.--MAELSTROM.

_Turn the broad helm, the fluttering canvas urge From Maelstrom's fierce innavigable surge._

CANTO III. l. 93.

On the coast of Norway there is an extensive vortex, or eddy, which lies between the islands of Moskoe and Moskenas, and is called Moskoestrom, or Maelstrom; it occupies some leagues in circ.u.mference, and is said to be very dangerous and often destructive to vessels navigating these seas. It is not easy to understand the existence of a constant descending stream without supposing it must pa.s.s through a subterranean cavity to some other part of the earth or ocean which may lie beneath its level; as the Mediterranean seems to lie beneath the level of the Atlantic ocean, which therefore constantly flows into it through the Straits; and the waters of the Gulph of Mexico lie much above the level of the sea about the Floridas and further northward, which gives rise to the Gulph-stream, as described in note on Ca.s.sia in Vol. II.

The Maelstrom is said to be still twice in about twenty-four hours when the tide is up, and most violent at the opposite times of the day. This is not difficult to account for, since when so much water is brought over the subterraneous pa.s.sage, if such exists, as compleatly to fill it and stand many feet above it, less disturbance must appear on the surface. The Maelstrom is described in the Memoires of the Swedish Academy of Sciences, and Pontoppiden's Hist. of Norway, and in Universal Museum for 1763, p. 131.

The reason why eddies of water become hollow in the middle is because the water immediately over the centre of the well, or cavity, falls faster, having less friction to oppose its descent, than the water over the circ.u.mference or edges of the well. The circular motion or gyration of eddies depends on the obliquity of the course of the stream, or to the friction or opposition to it being greater on one side of the well than the other; I have observed in water pa.s.sing through a hole in the bottom of a trough, which was always kept full, the gyration of the stream might be turned either way by increasing the opposition of one side of the eddy with ones finger, or by turning the spout, through which the water was introduced, a little more obliquely to the hole on one side or on the other. Lighter bodies are liable to be retained long in eddies of water, while those rather heavier than water are soon thrown out beyond the circ.u.mference by their acquired momentum becoming greater than that of the water. Thus if equal portions of oil and water be put into a phial, and by means of a string be whirled in a circle round the hand, the water will always keep at the greater distance from the centre, whence in the eddies formed in rivers during a flood a person who endeavours to keep above water or to swim is liable to be detained in them, but on suffering himself to sink or dive he is said readily to escape. This circulation of water in descending through a hole in a vessel Dr. Franklin has ingeniously applied to the explanation of hurricanes or eddies of air.

NOTE x.x.xII.--GLACIERS.