THE PROPOSED EXPERIMENTAL SOCIETY, 00000000 3 7 4 1 7 9 25 99999999,6 258 20 75 6 5999999 98 99999993 6,2 5 8 2 0 77 5 49 9 9 9 9 9 6 81 99999943 6 2,5 8 2 396 3 299 9 9 9 8 3 0 88 99999643 6 2 5,9 9 3 08 9 8999 9 6 7 9 2 6 34 99990643 6 5 8 0,6 6 74 2 19998 1 2 8 7 3 161 99970645 5 2 9 3 3,5 13 4 399882 5 8 2 11 7 34 99570762 9 4 7 2 1 7,79 9 8961368 6 6 5 2 4 9 60 90609394 2 8 1 9 6 8 19 × 3 2-71828182 8 4 5 9 0 46 =ε 23, Acton-street, Nov. 17, 1846. PREVENTION BY TELEGRAPH OF RAILWAY ACCIDENTS. Sir,-Oblige me by giving a place in your columns, should you consider it deserving, to the following plan of a telegraph for preventing collision on railways. For this end the two rails are to serve as conductors of electricity from the respective poles of a suitable voltaic arrangement placed at the station from which the train starts, the rails being rendered continuous conductors to the next station or division in advance, but no further-the intervention of a nonconducting substance there stopping the current. In these circumstances, it is to be observed, no transfer of electricity takes place, the current being open; as soon however as a train enters on that division of the rails, the circuit is completed through the conducting power of the carriage wheels and axle, or by means of a chain or wire carried by the train, the extremities of which are in contact with both rails. The electric current thus put in motion will continue to circulate until the train has reached the next station, and may be employed, as in the common telegraph, to turn an index or ring a bell, placed in the circle, at the station, afford. 499 THE PROPOSED EXPERIMENTAL SOCIETY. Sir, Every lover of philosophy must agree with the prefatory remarks of your correspondent, who suggests the publication by means of a society of all the now hidden knowledge of artizans and clever mechanics. One main difficulty would be the backwardness which all have to join a body of men who have but lately drawn together. Now, I think that your correspondent's views might become better known, and also the benefits of the system enhanced, if something of the following plan were adopted: You might print a circular to the mechanics of Britain, offering prizes, say one of 10%., two of 51., and four of 31., to be contended for by working men, who shall before some assigned date communicate any device in his trade, any simplification of the usual means of obtaining an endor any accredited invention not hitherto public; the communications to be examined by a board to be appointed; and every single trade to be included in the elegible candidates. Now, Sir, if you will forward such a thing, I myself will give half of each prize, and I am sure that there are many quite as willing to do what they can for so admirable an object. Trinity College, Nov. 16, 1846. J. M. [We are delighted to see the proposal of our correspondent, "A. H.," so nobly responded to, and from a quarter, too, where practical science has been generally supposed to be regarded with an indifference approaching to disdain. We incline very much towards the course which "J. M." recommends; but before committing ourselves to it, we think it due to "A. H.," with whom the plan originated, to wait for a communication of his sentiments upon it. Should "J. M.'s" plan be that ultimately adopted, we shall ourselves be happy to contribute the other half of the proposed prizes.— ED. M. M.] ANEMOMETERS. Trinity College, Nov. 16, 1846, Sir,-The attention of scientific men has lately been much directed to the improvement of anemometers. I shall bring before you, now, a construction which, while it registers the force and duration of every blast, will work at any distance from the observatory or place where it is put up. There is no friction beyond that of two pivots; and the instrument may be mounted upon the highest steeple I remain, your obedient servant, THE GUN COTTON IDENTICAL WITH XYLOÏDINE. At a meeting of the French Academy of Science on the 2nd inst., M. Pélouze ventured on the following anticipatory specification of M. Schönbein's invention: "Although M. Schönbein has not published the nature or mode of preparation of his cotton, it is evident that the properties which he assigns to it can only apply to xyloïdine. M. Dumas, as well as myself, made this remark in the origin of the first communications of M. Schönbein. Reasoning on the hypothesis that the poudre-coton is nothing else than xyloïdine, I may be permitted to say a few words with respect to its history, and of some of its properties. Xyloïdine was discovered, in 1833, by M. Braconnot, of Nancy. He prepared it by dissolving starch and some other organic substances in nitric acid, and precipitating these solutions in water. In a note inserted in the Comptes rendus de l'Académie des Sciences en 1838, I showed that the xyloïdine resulted from the union of the elements of the nitric acid with those of the starch, and explained by this composition the excessive combustibility of the substance produced. I ascertained-and this I think is a very important result in the history of the application of xyloïdine-that, instead of preparing it by dissolving the cellulose, it might be obtained with infinitely greater facility and economy by simply impregnating with concentrated nitric acid, paper, cotton, and hemp, and these organic matters thus treated took fire at 180 degrees, and burnt almost without residuum, and with excessive energy; but I think it right to add, that I never for an instant had an idea of their use as a substitute for gunpowder. The merit of this application belongs entirely to M. Schönbein. Eight years ago, however, I prepared an inflammable paper by plunging it into concentrated nitric acid. After leaving it there for twenty minutes, I washed it in a large quantity of water, and dried it in a gentle heat. I have recently tried this paper in a pistol; and with about three grains pierced a plank two centimètres in thickness (about three quarters of an inch) at a distance of 25 metres." [Mr. Schonbein gives the following contradiction to the above statement in a letter to the Times"Pélouze's Xyloidine is, according to the (own) statements of that distinguished chemist, readily soluble in acetic acid, forming, with the latter, a sort of varnish. The same acid has not the slightest action upon the gun-cotton, however long, and at what temperature soever, both substances are kept in contact with one another. The gun-cotton exhibits its full weight and explosive force after hav ing been treated with that acid for hours."—Es. M. M.] HOLTZAPFFel's turning AND MECHANICAL MANIPULATION. VOL. II. We have been looking with some impatience for the appearance of this second volume of Mr. Holtzapffel's admirable work, published full three years after the first, (see notice of vol. I. in the Mechanics' Magazine of 21st July, 1843,)-but an impatience which makes us only welcome and relish it "" the more, now that it is in our hands. We The subjects treated of in the present volume, under distinct chapters, are, Cutting Tools; Chisels and Planes; Turning Tools; Boring Tools; Screw Cutting Tools; Saws; Files; Sheers; and Punches. We proceed to extract a few specimens ; but with the intention of returning to the volume at an early opportunity. Angles of Cutting Tools. The angles of all tools are determined by the hardness, and the peculiarity of fibre or structure, of the several substances upon which they are employed. The woods and soft fibrous materials, require more acute angles than the metals and hard bodies; and the greater or less degree of violence to which the tools are subjected, greatly influences likewise the angles adopted for them. Thus, under the guidance of a little mechanism, the thin edge of a razor, which is sharpened at an angle of about 15 degrees, is used to cut minute slices or sections of woods, in all directions of the grain, for the purpose of the microscope. But the carpenter and others require more expeditious practice, and the first change is to thicken the edges of the tools to range from about 20 to 45 degrees, to meet the rough usage to which they are then exposed, whether arising from the knots and hard places in the woods, or the violence applied. In tools for iron and steel from 60 to 70 will be found a very common angle, in those for brass 80 to 90, in hexagonal broaches for metal it increases to 120, and in the oc 501 tagonal broach sometimes employed, the angle is still greater; in the circular broach required by clock and watchmakers, the angle disappears and the tool ceases either to cut or scrape, it resolves itself into an instrument acting by pressure, or becomes a burnisher. To a certain extent, every different material may be considered to demand tools of a particular angle, and again the angle is somewhat modified by the specific mode of employment: these conditions jointly determine the practical angles suited to every case, or the angles of greatest economy, or most productive effect. Independently of the measure of the angle of the tool, we have to consider its position as regards the surface of the work, the broad distinction being that, in the paring tools, the one face of the wedge or tool, is applied nearly parallel with the face of the work; and in the scraping tools, it is applied nearly at right angles, as explained in the foregoing definitions. Indeed the paring tools, if left to themselves, will in some cases assume the position named; thus for example, if we place a penknife at an elevated angle upon a cedar pencil, and attempt to carry it along as a carpenter's plane, the penknife, if held stiffly, will follow the line of its lower side and dig into the wood; but if it be held slenderly, it will swing round in the hand until its blade lies flat on the pencil, and it will even require a little twisting or raising to cause it to penetrate the wood at all. This disposition appears to be equally true, in the thin edges of the penknife or razor, and in the thick edges of the strong paring tools for metal. The action of a cutting-tool in motion is twofold. The moving force is first exerted on the point of the wedge, to sever or divide the substance particle from particle; the cohesion of the mass now directly opposes the entry of the tool, and keeps it back. But the primary motion impressed on the tool having severed a shaving, proceeds to bend or curl it out of the way; the shaving ascends the slope of the wedge, and the elasticity of the shaving confines the tool in the cleft, presses it against the lower side, disposes it to pursue that line, and therefore to dig into the substance. Velocity of Cutting Tools. The principal limit of velocity in cutting machines, appears to be the greatest speed the tool will safely endure, without becoming so heated by the friction of separating the fibres, as to lose its temper or proper degree of hardness. The cohesion of iron being very considerable, a velocity materially exceeding ten to twenty feet per minute, would soften and discolour the tool, whereas in general the tools for iron are left nearly or quite hard. Brass having much less cohesion than iron, allows a greater velocity to be used, lead and tin admit of still more speed, and the fibrous cohesion of the soft woods is so small, that when the angles of the tools are favourable, there is hardly a limit to the velocity which may be used. Water, soap and water, oil, milk, and other fluids, are in many cases employed, and especially with the more fibrous metals, for the purpose of lubricating the cutting edges of the tools to keep down the temperature, the fluids reduce the friction of separating the fibres, and cool both the tool and work, thereby allowing an increase of velocity; and at the same time they lessen the deterioration of the instrument, and which when blunted excites far more friction, and is likewise more exposed to being softened, than when keen and in perfect working order. There are, however, various objections to the constant use of lubricating fluids with cutting tools. Planing Machines. These several machines are compounds of slides and guides, and of fixed or revolving planes: the relative degrees of perfection attained, depend on the stability of the machines, and their respective agreement with the principles of the ordinary hand tools, which are generally themselves the last stages of a long series of gradual improvements. But the absence of some of the true characters of the plane, in nearly the whole of the machines for wood, namely, the proper obliquities of the iron, the frequent want of the mouth of the plane, and of the top or breaker iron, which so greatly restrains the splitting and tearing up of the fibres, prevent the machines from producing, in the softer woods, the smooth finished work of hand tools, in the management of which the judgment of the operator can be employed to combat the peculiarities of fibre. But the enormous productive powers of such machines, outweigh these drawbacks, and the more especially so, as the general forms or outlines are repeated by them in a most exact manner, and a little after-trimming by hand imparts the necessary finish. In speaking of the apparatus for ornamental turning, there will be occasion to show that the same principles are strictly embodied in miniature, in the various parts of the complex lathe for ornamental turning; but as the hard wood and ivory therein generally used, admit of the employment of scraping tools, not requiring either the obliquity of the cutter, or the mouth of the plane, the above objections do not apply to them, and their several results exhibit a much nearer approach to perfection. Metal Turning. The softest of the metals, such as lead, tin, and soft pewter, may be turned with the ordinary tools for soft wood; but for the harder metals, such as zinc, and hard alloys containing much antimony, the tools resemble those used for the hard woods, and they are mostly employed dry. Copper, which is much harder and tougher, is turned with tools similar to those for wrought-iron, but in general they are sharpened a little more keenly, and water is allowed to drop upon the work, to lessen the risk of dragging or tearing up the face of the copper, a metal that neither admits of being turned or filed with the ordinary facility of most others. Silver and gold, having the tenacious character of copper, require similar turning tools, and they are generally lubricated with milk. In the above, and nearly all the metals except iron and those of equal or superior hardness, there seems a disposition to adhere, when, by accident, the recently removed shaving gets forcibly pressed against a recently exposed surface, (the metals at the time being chemically clean,) this disposition to unite is nearly prevented when water or other fluid is used. Water is occasionally resorted to in turning wrought iron and steel; this causes the work to be left somewhat smoother, but it is not generally used, as it is apt to rust the machinery; oil fulfils the same end, but is too expensive for general purposes. Cast-iron having a crystalline structure, the shavings soon break, without causing so much friction as the hard ductile metals; cast-iron is therefore always worked dry, even when the acute edges of 60 degrees are thickened to those of 80 or 90, either from necessity, as in some of the small boring tools, or from choice on the score of durability, as in the largest boring tools and others. Brass and gun-metal are also worked dry, although the turning tools are nearly rectangular, as the copper becomes so far modified by the zinc or tin, that the alloys, although much less crystalline than castiron, and less ductile than copper, yield to the turning tools very cleanly without water. But when the various tools with rectangular edges are used for wrought iron and steel, on account of the greater cohesion of these materials, they must be lubricated with oil, grease, soap and water, or other matter, to prevent the metals from being torn. And the screw cutting tools, many of which present much surface friction, and also rectangular or still more obtuse edges, almost invariably require oil or other unctuous fluids, for all the metals upon which they are employed. |