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hitherto been given. Perhaps it may be this, | down, and let the air pass out at E, which that great part of the force employed contri- striking forcibly against the water abaft must butes little to the motion. For instance, (fig. push the boat forward. If there is added an air 12) of the four paddles a, b, c, d, all under vessel F properly valved and placed, the force water, and turning to move a boat from X to would continue to act while a fresh stroke is Y, c has the most power, b nearly though taken with the lever. The boatman might not quite as much, their motion being nearly stand with his back to the stern, and putting horizontal; but the force employed in moving his hands behind him, work the motion by a, is consumed in pressing almost downright taking hold of the cross bar at B, while anoupon the water till it comes to the place of ther should steer; or if he had two such b; and the force employed in moving d is pumps, one on each side of the stern, with a consumed in lifting the water till d arrives at lever for each hand, he might steer himself the surface; by which means much of the la- by working occasionally more or harder with bour is lost. It is true, that by placing the either hand, as watermen now do with a pair wheels higher out of the water, this waste la- of sculls. There is no position in which the bour will be diminished in a calm, but where body of a man can exert more strength than a sea runs, the wheels must unavoidably be in pulling right upwards. To obtain more swiftoften dipt deep in the waves, and the turn-ness, greasing the bottom of a vessel is someing of them thereby rendered very laborious to little purpose.

times used, and with good effect. I do not know that any writer has hitherto attempted to explain this. At first sight one would imagine, that though the friction of a hard body, sliding on another hard body, and the resist

minished by putting grease between them, yet that a body sliding on a fluid, such as water, should have no need of, nor receive any advantage from such greasing. But the fact is not disputed. And the reason perhaps may be this-The particles of water have a mutual attraction, called the attraction of adhesion. Water also adheres to wood, and to many other substances, but not to grease: on the contrary they have a mutual repulsion, so that it is a question whether when oil is poured on water, they ever actually touch each other; for a drop of oil upon water, instead of sticking to the spot where it falls, as it would if it fell on a looking-glass, spreads instantly to an immense distance in a film extremely thin, which it could not easily do if it touched and rubbed or adhered even in a small degree to the surface of the water. Now the adhesive force of water to itself, and to other substances, may be estimated from the weight of it necessary to separate a drop, which adheres, while growing, till it has weight enough to force the separation and break the drop off. Let us suppose the drop to be the size of a pea, then there will be as many of these adhesions as there are drops of that size touching the bottom of a vessel, and these must be broken by the moving power, every step of her motion that amounts to a drop's breadth and there being no such adhesions to break between the water and a greased bottom, may occasion the difference.

Among the various means of giving motion to a boat, that of M. Bernoulli appears one of the most singular, which was to have fixed in the boat a tube in the form of an L, the up-ance occasioned by that friction, might be diright part to have a funnel-kind of opening at top, convenient for filling the tube with water; which, descending and passing through the lower horizontal part, and issuing in the middle of the stern, but under the surface of the river, should push the boat forward. There is no doubt that the force of the descending water would have a considerable effect, greater in proportion to the height from which it descended; but then it is to be considered, that every bucket full pumped or dipped up into the boat, from its side or through its bottom, must have its viz inertia overcome so as to receive the motion of the boat, before it can come to give motion by its descent; and that will be a deduction from the moving power. To remedy this, I would propose the addition of another such L pipe, and that they should stand back to back in the boat thus, figure 13, the forward one being worked as a pump, and sucking in the water at the head of the boat, would draw it forward while pushed in the same direction by the force at the stern. And after all it should be calculated whether the labour of pumping would be less than that of rowing. A fire-engine might possibly in some cases be applied in this operation with advantage. Perhaps this labour of raising water might be spared, and the whole force of a man applied to the moving of a boat by the use of air instead of water; suppose the boat constructed in this form, figure 14. A, a tube round or square, of two feet diameter, in which a So much respecting the motion of vessels. piston may move up and down. The piston to But we have sometimes occasion to stop their have valves in it, opening inwards, to admit motion; and if a bottom is near enough we air when the piston rises; and shutting, when can cast anchor: where there are no soundit is forced down by means of the lever B turn-ings, we have as yet no means to prevent ing on the centre C. The tube to have a driving in a storm, but by lying-to, which still valve D, to open when the piston is forced permits driving at the rate of about two miles

an hour; so that in a storm continuing fifty hours, which is not an uncommon case, the ship may drive one hundred miles out of her course; and should she in that distance meet with a lee shore, she may be lost.

To prevent this driving to leeward in deep water, a swimming anchor is wanting, which ought to have these properties.

1. It should have a surface so large as, being at the end of a hauser in the water, and placed perpendicularly, should hold so much of it, as to bring the ship's head to the wind, in which situation the wind has least power to drive her.

2. It should be able by its resistance to prevent the ship's receiving way.

3. It should be capable of being situated below the heave of the sea, but not below the undertow.

4. It should not take up much room in the ship.

5. It should be easily thrown out, and put into its proper situation.

6. It should be easy to take in again, and stow away.

An ingenious old mariner, whom I formerly knew, proposed, as a swimming anchor for a large ship, to have a stem of wood twentyfive feet long and four inches square, with four boards of 18, 16, 14 and 12 feet long, and one foot wide, the boards to have their substance thickened several inches in the middle by additional wood, and to have each a four inch square hole through its middle, to permit its being slipt on occasionally upon the stem, and at right angles with it; where all being placed and fixed at four feet distance from each other, it would have the appearance of the old mathematical instrument called a forestaff. This thrown into the sea, and held by a hauser veered out at some length, he conceived would bring a vessel up, and prevent her driving, and when taken in might be stowed away by separating the boards from the stem. (Figure 15.) Probably such a swimming anchor would have some good effect, but it is subject to this objection, that laying on the surface of the sea, it is liable to be hove forward by every wave, and thereby give so much leave for the ship to drive.

Two machines for this purpose have occurred to me, which, though not so simple as the above, I imagine would be more effectual, and more easily manageable. I will endeavour to describe them, that they may be submitted to your judgment, whether either would be serviceable; and if they would, to which we should give the preference. The first is to be formed, and to be used in the water on almost the same principles with those of a paper kite used in the air. Only as the paper kite rises in the air, this is to descend in the water. Its dimensions will be different for ships of different size.

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To make one of suppose fifteen feet high; take a small spar of that length for the backbone, A B, figure 16, a smaller of half that length C D, for the cross piece. Let these be united by a bolt at E, yet so as that by turning on the bolt they may be laid parallel to each other. Then make a sail of strong canvas, in the shape of figure 17. To form this, without waste of sail-cloth, sew together pieces of the proper length, and for half the breadth, as in figure 18, then cut the whole in the diagonal lines a, b, c, and turn the piece F so as to place its broad part opposite to that of the piece G, and the piece H in like manner opposite to I, which when all sewed together will appear as in fig. 17. This sail is to be extended on the cross of fig. 16, the top and bottom points well secured to the ends of the long spar; the two side points d, e, fastened to the ends of two cords, which coming from the angle of the loop (which must be similar to the loop of a kite) pass through two rings at the ends of the short spar, so as that on pulling upon the loop the sail will be drawn to its extent. The whole may, when aboard, be furled up, as in figure 19, having a rope from its broad end, to which is tied a bag of ballast for keeping that end downwards when in the water, and at the other end another rope with an empty keg at its end to float on the surface; this rope long enough to permit the kite's descending into the undertow, or if you please lower into still water. It should be held by a hauser. To get it home easily, a small loose rope may be veered out with it, fixed to the keg. Hauling on that rope will bring the kite home with small force, the resistance being small, as it will then come end ways.

It seems probable that such kite at the end of a long hauser would keep a ship with her head to the wind, and, resisting every tug, would prevent her driving so fast as when her side is exposed to it, and nothing to hold her back. If only half the driving is prevented, so as that she moves but fifty miles instead of the hundred during a storm, it may be some advantage, both in holding so much distance as is saved, and in keeping from a lee-shore. If single canvas should not be found strong enough to bear the tug without splitting, it may be doubled, or strengthened by a netting behind it, represented by figure 20.

The other machine for the same purpose, is to be made more in the form of an umbrella, as represented, figure 21. The stem of the umbrella, a square spar of proper length, with four moveable arms, of which two are represented C, C, figure 22. These arms to be fixed in four joint cleats, as D, D, &c. one on each side of the spar, but so as that the four arms may open by turning on a pin in the joint. When open they form a cross, on which a four-square canvas sail is to be extended,

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its corners fastened to the ends of the four, he added, they are carried back by the curarms. Those ends are also to be stayed by rent more than they are forwarded by the ropes fastened to the stem or spar, so as to wind: and if the wind be good, the subtrackeep them short of being at right angles tion of 70 miles a day from their course is of with it and to the end of one of the arms some importance. I then observed it was a should be hung the small bag of ballast, and pity no notice was taken of this current upon to the end of the opposite arm the empty keg. the charts, and requested him to mark it out This, on being thrown into the sea, would for me, which he readily complied with, addimmediately open; and when it had performed ing directions for avoiding it in sailing from its function, and the storm over, a small rope Europe to North America. I procured it to be from its other end being pulled on, would turn engraved by order from the general post-office, it, close it, and draw it easily home to the ship. on the old chart of the Atlantic, at Mount and This machine seems more simple in its opera- Page's Tower-hill; and copies were sent tion, and more easily manageable than the down to Falmouth for the captains of the pacfirst, and perhaps may be as effectual.* kets, who slighted it however; but it is since printed in France, of which edition I hereto annex a copy." *

Vessels are sometimes retarded, and sometimes forwarded in their voyages, by currents at sea, which are often not perceived. About This stream is probably generated by the the year 1769, or 70, there was an application great accumulation of water on the eastern made by the board of customs at Boston, to coast of America between the tropics, by the the lords of the treasury in London, complain- trade-winds which constantly blow there. It ing that the packets between Falmouth and is known that a large piece of water ten miles New York, were generally a fortnight longer broad and generally only three feet deep, has in their passages, than merchant-ships from by a strong wind had its waters driven to one London to Rhode-Island, and proposing that side and sustained so as to become six feet for the future they should be ordered to Rhode- deep, while the windward side was laid dry. Island instead of New York. Being then This may give some idea of the quantity concerned in the management of the Ameri- heaped up on the American coast, and the can post-office, I happened to be consulted on reason of its running down in a strong current the occasion; and it appearing strange to me through the islands into the bay of Mexico, that there should be such a difference between and from thence issuing through the gulf of two places, scarce a day's run asunder, espe- Florida, and proceeding along the coast to the cially when the merchant-ships are generally banks of Newfoundland, where it turns off todeeper laden, and more weakly manned than wards and runs down through the Western the packets, and had from London the whole Islands. Having since crossed this stream length of the river and channel to run before several times in passing between America and they left the land of England, while the Europe, I have been attentive to sundry cirpackets had only to go from Falmouth, I could cumstances relating to it, by which to know not but think the fact misunderstood or mis- when one is in it; and besides the gulph weed represented. There happened then to be in with which it is interspersed, I find that it is alLondon a Nantucket sea-captain of my ac- ways warmer than the sea on each side of it, quaintance, to whom I communicated the and that it does not sparkle in the night: Í affair. He told me he believed the fact might annex hereto the observations made with the be true; but the difference was owing to this, thermometer in two voyages, and possibly that the Rhode-Island captains were acquaint- may add a third. It will appear from them, ed with the gulf stream, which those of the that the thermometer may be an useful inEnglish packets were not. We are well ac-strument to a navigator, since currents comquainted with that stream, says he, because in our pursuit of whales, which keep near the sides of it, but are not to be met with in it, we run down along the sides, and frequently cross it to change our side: and in crossing it have sometimes met and spoke with those packets, who were in the middle of it, and stemming it. We have informed them that they were stemming a current, that was against them to the value of three miles an hour; and advised them to cross it and get out of it; but they were too wise to be counselled by simple Amecan fishermen. When the winds are but light,

* Captain Truxton, on board whose ship this was written, has executed this proposed machine; he has given six arms to the umbrella, they are joined to the stem by iron hinges, and the canvas is double. He has taken it with him to China. February, 1786.

ing from the northward into southern seas, will probably be found colder than the water of those seas, as the currents from southern seas into northern are found warmer. And it is not to be wondered that so vast a body of deep warm water, several leagues wide, coming from between the tropics and issuing out of the gulph into the northern seas, should retain its warmth longer than the twenty or thirty days required to its passing the banks of Newfoundland. The quantity is too great, and it is too deep to be suddenly cooled by passing under a cooler air. The air immedi

*The map in this edition has beeen constructed so as to embrace in one view, the theory of the Gulf Stream and the theory of the migration of fish; some attention has been paid also to Volney's suggestions on the subject of the Gulf Stream. See the plate.

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