An extraordinary instance of this kind is mentioned at Bathsha, a port in the kingdom of Tonquin in the East Indies, of northern latitude 20° 50′. The day in which the moon passes the equator, the water stagnates there without any motion: as the moon removes from the equator, the water begins to rise and fall once a day; and it is high water at the setting of the moon, and low water at her rising. This daily tide increases for about seven or eight days, and then decreases for as many days by the same degrees, till this motion ceases when the moon has returned to the equator. When she has passed the equator, and declines towards the south pole, the water rises and falls again, as before; but it is high water now at the rising, and low water at the setting, of the moon.
We shall close this chapter with an account of the remarkable fact of Waves stilled by Oil.—This wonderful property, though well known to the ancients, as appears from the writings of Pliny, was for many ages either quite unnoticed, or treated as fabulous by succeeding philosophers, till Dr. Franklin again attracted the attention of the learned to this subject; though it appears, from some anecdotes, that seafaring people have always been acquainted with it. Mr. Pennant, in his British Zoology, vol. iv. under the article Seal, takes notice, that when these animals are devouring a very oily fish, which they always do under water, the waves above are remarkably smooth; and by this the fishermen know where to find them. Sir Gilbert Lawson, who served long in the army at Gibraltar, assured Dr. Franklin, that the fishermen in that place are accustomed to pour a little oil on the sea, in order to still its motion, that they may be enabled to see the oysters lying at its bottom, which are there very large, and which they take up with a proper instrument. A similar practice is followed among fishermen in various other parts; and Dr. Franklin was informed by an old sea captain, that the fishermen of Lisbon, when about to return into the river, if they saw too great a surf upon the bar, would empty a bottle or two of oil into the sea, which would suppress the breakers, and allow them to pass freely. The Doctor having revolved in his mind all these pieces of information, became impatient to try the experiment himself. At last, having an opportunity of observing a large pond very rough with the wind, he dropped a small quantity of oil upon it. But having at first applied it on the lee side, the oil was driven back again upon the shore. He then went to the windward side, and poured on about a tea-spoonful of oil; this produced an instant calm over a space several yards square, which spread amazingly, and extended itself gradually till it came to the lee-side; making all that quarter of the pond, perhaps half an acre, as smooth as glass. This experiment was often repeated in different places, and was always attended with success.
CHAP. XLV.
CURIOSITIES RESPECTING THE SEA.—(Concluded.)
| “—————————Adoring, own The hand Almighty, who its channel’d bed Immeasurable sunk, and pour’d abroad, Fenc’d with eternal mounds, the fluid sphere; With every wind to waft large commerce on, Join pole to pole, consociate sever’d worlds, And link in bonds of intercourse and love Earth’s universal family.” |
On the Perfection of Navigation.
The following account of the present wonderful perfection of navigation, is taken from a History of Voyages and Discoveries made in the North; translated from the German of John Reinhold Foster, LL.D.—
“Of all the arts and professions which have at any time attracted notice, none has ever appeared to be more astonishing and marvellous than that of navigation, in the state in which it is at present; an art which doubtless affords one of the most certain irrefragable proofs of the amazing powers of the human understanding. This cannot be made more evident, than when, taking a retrospective view of the tottering inartificial craft to which navigation owes its origin, we compare it to a noble and majestic edifice, containing 1000 men, together with their provisions, drink, furniture, wearing-apparel, and other necessaries, for many months, besides 100 pieces of heavy ordnance; and bearing all this vast apparatus safely, and as it were on the wings of the wind, across immense seas to the most distant shores. The following example may serve for the present to delineate at full length, as it were, the idea above alluded to. But first I must premise, that a huge unwieldy log of wood, with the greatest difficulty, and in the most uncouth manner, hollowed out in the inside, and somewhat pointed at both ends, and in this way set on a river for the purpose of transporting two or three persons belonging to one and the same family, across a piece of water a few feet deep, by the assistance of a pole pushed against the ground, cannot with any propriety be considered as the image of navigation in its first and earliest stage. For it seems evident to me, that people in the beginning only took three or four trunks of trees, and fastened them together, and then, by means of this kind of raft, got across such waters as were too deep for them to ford, and across which they could not well swim, with their children, and various kinds of goods which they might wish to preserve from being wet. The canoe, however, is a specimen of the art in a more advanced state, as this kind of craft is capable of having direction given to it, and even of so capital an improvement as that of having a sail added to it. For this reason I choose this vehicle for a standard, in preference to a mere raft, to which, imperfect as it is, it is so much superior.
“Let us, then, compare this with a large majestic floating edifice, the result of the ingenuity and labour of many hundreds of hands, and composed of a number of well-proportioned pieces, nicely fastened together by iron nails and bolts; and rendered so tight with tow and pitch, that no water can penetrate it. Now, in order to give motion and direction to this enormous machine, some astonishingly lofty pieces of timber have been fixed upright in it, and so many moveable cross pieces have been added to it, together with such a variety of pieces of strong linen cloth, for the purpose of catching the wind, and of receiving its impulse and propelling power, that the number of them amounts to upwards of thirty. For changing the direction of the yards and sails, according to particular circumstances, it has also been requisite to add a vast quantity of cordage and tackling; and nevertheless, even all this would not be sufficient for the perfect direction and government of the vessel, if there were not fastened to the hinder part of it, by means of hinges and hooks, a moveable piece of wood, very small indeed, in proportion to the whole machine, but the least inclination of which to either side is sufficient to give immediately a different direction to this enormously large mass, and that even in a storm, so that two men may direct and govern this swimming island with the same, or with greater ease, than a single man can do a boat. But if, besides, we consider, that, in a vessel like this, not a single piece is put in at random, but that every part of it has its determinate measure and proportion, and is fixed precisely in that place which is the most advantageous for it; that, throughout every part of it, there is distributed an astonishing quantity of blocks, stays, and pulleys, for the purpose of diminishing the friction, and of accelerating the motion of these parts; that even the bellying and vaulted part of the fabric, together with its sharp termination underneath, are proportioned according to the nicest calculations, and the most accurately determined rules; that the length and the thickness of the masts, the size of the booms and yards, the length, width, and strength of the sails and tackling, are all in due proportion to each other, according to certain rules founded upon the principles of motion: when we consider all this, I say, our admiration increases more and more at this great masterpiece of human power and understanding.