93-A ship-raising engine. 94-A pocket engine to open any door. 95-A double cross-bow. 96-A way for sea banks. 97-A perspective instrument. 99-A most admirable way to raise weights.* 100-A stupendous water-work. and Forces. On the Equal Action and Reaction of Motions This truth has otherwise been expressed -"action and reaction are equal and contrary." It is clear that if no action or move. ment takes place on earth but in consequence of either attraction or repulsion-and this has now been shown-there must always be two objects or masses concerned, and each must be attracted or repelled just as much as the other, although one will have less velo. city than the other, as it may be itself greater, or fixed to another mass. If a man in one boat pull at a rope attached to another, the two boats will approach. If they be of equal size and load, they will 75-A discourse woven in tape or ribbon.§ both move at the same rate, in whichever of 76-To write in the dark. 77-A flying man. 78-A continually going watch. 79-A total locking of cabinet boxes. 80-Light pistol barrels. 81-A combe-conveyance for letters.** 82-A knife, spoon, or fork conveyance. 83-A rasping mill. 64-An arithmetical instrument. 85-An untoothsome pear. 86-An imprisoning chair. 87-A eandle mould. the boats the man may be ; and if there be a difference in the sizes, and resistances, there will be a corresponding difference in the velocities, the smaller boat moving the fastest. A magnet and a piece of iron attract each other equally, whatever disproportion there is between the masses. If either be balanced in a scale, and the other be then brought within a certain distance beneath it, the very same counterpoise will be required to prevent their approach, whichever be in the 88-A brazen head, or speaking figure.tt scale. If the two were hanging near each 89-Primero gloves.++ 90-A dicing-box.§§ 91-An artificial ring-horse. 92-A gravel engine. • Foreacres. + "For whole cannon." A whole side of-wanting. Or ribbon-wanting. A continual watch." A total-wanting. **"81, 82. Conveyance for letters." ++ Wanting entirely in the MS. # "Stamping engine." $$ " Primero gloves" The Marquis seems to have been in doubt which he should erse-the brazen head or the dicing-box. other as pendulums, they would approach and meet; but the little one would perform more than half of the journey. A man in a boat pulling a rope attached to a large ship, seems only to move the boat: but he really moves the ship a little, for, supposing the resistance of the ship to be just a thousand times greater than that of the boat, a thousand men in a thousand boats, pulling simultaneously in the same manner, would make the ship meet them half way. A pound of lead and the earth attract each other with equal force, but that force makes the lead approach sixteen feet in a second * Wanting in the MS On the Equal Action and Reaction of Motions and Forces. owards the earth, while the contrary motion of the earth is of course as much less than this as the earth is weightier than one pound and is therefore unnoticed. Speaking strictly, it is true, that even a feather falling lifts the earth towards it, and that a man jumping kicks the earth away. A spring unbending between two equal bodies, throws them off with equal velocity; if between bodies of different magnitudes the velocity is greater in the smaller body, and in proportion to the smallness. On firing a cannon, the gun recoils with even more motion or momentum in it than the ball has, for it suffers the reaction of the expelled gun-powder as well as of the ball; but the momentum in the gun being diffused through a greater mass, the velocity is small, and easily checked. In the art of projectiles, it has lately been proposed, as promising a great saving of weight in the field or on ship board, besides other advantages, that instead of shooting round bullets from a great barrel or cannon, as at present, the bullets should be made somewhat of barrel-shape, or should have a small barrel as a tail, and should be shot way from a strong fixed spindle or close fit. ing ramrod, which would then constitute the piece of ordnance. Such a projectile, for the reason stated in the last paragraph, receives more momentum from a given quanti. ty of gunpowder than a common ball does. The experiment has been tried by the inge. nious proposer, Mr. Levier, with satisfactory result. The recoil of a light fowling-piece will hurt the shoulder, if the piece be not held close to it. A ship in chase, by firing her bow guns, retards her motion; by firing from her stern she quickens it. A ship firing a broadside heels or inclines to the opposite side. A vessel of water suspended by a cord hangs perpendicularly; but if a hole be opened in one side, so as to allow the water to jet out there, the vessel will be pushed to the other side by the reaction of the jet, and will so remain while it flows. If the hole be oblique, the vessel will turn round constantly. A vessel of water placed upon a floating piece of plank, and allowed to throw out a jet, as in the last case, moves the plank in the opposite direction. A steamboat may be driven by making the engine pump or squirt water from the stern, instead of making it, as usual, move paddle. 93 wheels. There is a loss of power however in this mode of applying it, as will be explained under the head of "Hydraulics." A man floating in a small boat, and blowing strongly with a bellows towards the stera, pushes himself onwards with the same force with which the air issues from the bel. lows pipe. A sky-rocket ascends, because, after it is lighted, the lower part is always producing a large quantity of aeriform fluid, which, in expanding, presses not only on the air below, but also on the rocket above, and thus lifts it. The ascent is aided also by the recoil of the rocket from the part of its substance, which is constantly bursting downwards. He was a foolish man who thought he had found the means of commanding always a fair wind for his pleasure-boat, by erecting an immense bellows in the stern. The bel lows and sails acted against each other, and there was no motion: indeed, in a perfect calm, there would be a little backward motion, because the sail would not catch all the wind from the bellows. A man supported on a floating plank, by walking towards one end of it gives it a mo. tion in the direction opposite. A man using an oar, or a steam-engine turning paddle-wheels, advances exactly with the force that drives the water astern. A swimmer pressing the water downwards and backwards with his hands, is sent forwards and upwards with the same force, by the reaction of the water. And a bird flying is upheld with exactly the force with which it strikes the air in the opposite direction. A man pushing against the ground with a stick may be considered as compressing a spring between the earth and the end of his stick, which spring is therefore pushing him up as much as he pushes down; and if, at the time, he were balanced in the scale of a weighing beam, he would find that he weighed just as much less as he was pressing with his stick. Thus an invalid, on a spring plank or chair, who, by a trifling downward pressure of his hand on a staff or on a table, causes his body to rise and fall through a great range, and thus obtains the advantage of almost passive exercise, is really lifting himself while he presses downward. When a child cries, on knocking his head against a table or pane of glass, it is common to tell him, and it is true, that he has given as hard a blow as he has received; al though his philosophy, probably, looking chiefly to results, blames the table for his head hurt, and his head for the glass broken. The difference of momentum acquired in a fall of one foot or of several is well known: the corresponding intensities of reaction are unpleasantly experienced by a man who, in sitting down where he supposed a chair to be, unexpectedly reaches the floor. What motion the wind has given to a ship it has itself lost, that is to say, the ship has reacted on the moving air: as is seen when one vessel is becalmed on the lee of another. When one billiard ball strikes directly another ball of equal size it stops, and the second ball proceeds with the whole velocity which the first had-the action which imparts the new motion being equal to the reaction which destroys the old. Although the transference of motion, in such a case, seems to be instantaneous, the change is really progressive, and as follows. The approaching ball, at a certain point of time, has just given half of its motion to the other equal ball, and if both were of soft clay, they would then proceed together with half the original velocity; but, as they are elastic, the touching parts at the moment supposed are compress. ed like a spring between the balls, and by then expanding, and exerting force equal. ly both ways, they double the velocity of the foremost ball, and destroy altogether the motion of that behind. If a billiard ball be propelled against the nearest one of a row of balls equal to itself, it comes to rest as in the last case described, while the farthest ball of the row darts off with its velocity-the intermediate balls hav. ing each received and transmitted the motion in a twinkling, without appearing themselves to move. As further illustrative of the truths, that action and reaction are equal and contrary, and that in every case of hard bodies striking each other, they may be regarded as compressing a very small strong spring between them, we may mention, that when any elas. tic body, as a billiard ball, strikes another body larger than itself, and rebounds, it gives to that other, not only all the motion which it originally possessed, this being done at the moment when it comes to rest, but an additional quantity, equal to that with which it recoils-owing to the equal action in both directions of the repulsion or spring which causes the recoil. When the difference of size between the bodies is very great, the returning velocity of the smaller is nearly as great as its advancing motion was, and thus it gives a momentum to the body struck, near. ly double of what it originally itself possessed. This phenomenon constitutes the paradoxical case of an effect being greater than its cause, and has led persons, imperfectly acquainted with the subject, to seek from the principle a perpetuum mobile. A hammer on rebounding from an anvil has given a blow of nearly double the force which it had itself, for the anvil felt its full original force while stopping it, and then, equally with itself, was affected by the repulsion which caused its return. Many more interesting facts might be adduced as examples of equal action and reaction, but these will suffice. Canning's Life-Raft. By W. BADDELEY. [From the London Mechanics' Magazine.] SIR, It is probable that during the last summer many of your readers may have seen on the River Thames, in the vicinity of New London and Blackfriars Bridges, a singularlooking machine, composed of spars and floated by barrels, the object of which was not very apparent. The machine is, however, one of considerable importance to the maritime world, being a life-raft, invented by Mr. Alfred Canning, R. N. for the relief of persons in danger of shipwreck; and as a knowledge of its construction cannot be too widely circulated, I beg to submit the following description for insertion in your Magazine. There are two forms of Mr. Canning's raft, as represented by figs. 1 and 2. In fig. 1, A is a main-yard or other spar, with two cross-spars, bb, lashed near each end of it, and kept in their places by the rope or stays cc. To give the necessary firmness to the machine, four of the ropes terminate in a loop at dd, through which a smaller cord is rove, and braced up taut. The machine is floated by means of emp. ty water-casks, one being attached to each end of the cross-spars b b. The projecting end of each cask is covered with a hammock, to protect them from being stove in by rocks, &c. &c. The number and disposition of the casks must, of course, be regulated by the number of persons to be carried. When the number is great, it is advisable to place the barrels as shown by the dotted lines, to obtain sufficient buoyancy. The raft exhib. ited on the river was so supported. A platform e, for the reception of passengers, is slung upon the main-yard A by a strong loop, so as to turn freely upon it; one or two loops being used, according to the size of platform required. The loops are kept in the middle of the yard by a chock on each side of them. It will be observed that only four of the casks can be immersed at one time, and the object of the inventor in using twice that number is to permit the raft to roll over, without any risk to the parties on the platforme: that being suspended as just described, so as to retain a horizontal position, whichever set of barrels may be undermost. Fig. 2 shows another modification of this raft. It is composed of three spars, lashed together crosswise at the middle, and braced up by means of the ropes fff To each end of these spars (for the sake of clearness, only one is shown in the drawing,) is attached an empty cask, or a cork-fender, to give a requisite buoyancy. If casks are used, they should be protected with hammocks, as be fore described. The persons upon this raft support themselves in the centre, holding on by the ropes, and shifting themselves when. ever the raft rolls over. 'It is right to state that the merits of this raft do not rest upon fresh-water experiments: Mr. Canning having made numerous trials with it on various parts of the French and English coasts, with invariable success, par. ticularly at Cherbourg and Jersey. At the former place, a raft of the description shown at fig. 1 was drawn out to the head of the jetty in very stormy weather: Mr. Can. ning having seated himself on the platform, the raft was turned adrift, and was driven by the wind across the mouth of the harbor upon the rocks, and was eventually thrown by the waves, high and dry, upon a shore of the most dangerous character, without any inju. ry either to the machine or to Mr. Canning. The machine possesses the requisite firm. ness and stability, with just so much elasti. city as is necessary for its safety. It carries and explained the construction of his raft, in the persons on it higher, and consequently a lecture delivered to the members of the drier, than any other raft; and is perfectly Mechanics' Institution, in which he gave an safe and certain on shores where a life-boat interesting account of several of his experi would inevitably be dashed to pieces. The ments in different places, and expressed his materials of which it is composed are such readiness to put to sea in the severest storm, as may be found on board almost every ship, on any part of the British coast: thereby and the raft may be put together in a com- showing his perfect confidence in the safety paratively short period of time. and efficiency of his simple life-raft. When a vessel has been wrecked on a lee. shore, and a communication formed by means of Captain Manby's apparatus, or the more recent improvements of Mr. Murray, this raft would be found a most eligible mode of landing the crew. Mr. Canning, some time since, exhibited The Society of Arts have presented Mr. Canning with their large silver medal, as a token of the high opinion they entertain of the ingenuity of his contrivance; and I guess it will be some time before they have an opportunity of rewarding another of equal merit. METEOROLOGICAL RECORD, FOR THE WEEK ENDING MONDAY, FEBRUARY 25, 1833. KEPT IN THE CITY OF NEW-YORK. [Communicated for the American Mechanics' Magazine.] |