engine, leaves 226 tons for the load, only about 3 tons above what the engine drew. Hence, if Ww we have sin z= b b-t= The general estimate of the force of traction on a level railway is 9 lbs. to a ton; but Mr. Dixon told me he thought it approached nearer to 10lbs. If, therefore, we take 94lbs., which gives th, the usual estimate, we cannot err much. This being settled, the following experi inent, before alluded to, on the Runcorn and St. Helen's Railway, April 11, 1834, will afford us the means of determining the value of the bite :-An engine called the "Director," 94 tons, with coupled wheels, dragging her tender 3 tons, and two waggons of coal 13 tons, started from a little way below the commencement of a plane rising for some distance from the bottom 1 in 30, and near the top 1 in 26. On the engine were two men, and on the tender myself and two others, as far as I remember. One of the men held the escape-valve firmly down, which enabled us slowly to reach the summit; but it was evidently a maximum effort. Presuming the weights and inclination to be right, we have W 94 +34 + 131⁄2= 26, w = 9, sin z = 26, and, as before, t= Consequently, 10 1 9.84' th, which I have reason to believe is a reasonable estimate of the bite. It also agrees very nearly with another experiment on the Sutton inclined plane I attended with the "Etna" engine, and with the celebrated exploit of the " Sampson," weighing 9 tons, 17 cwt., with coupled wheels. This engine being helped up the inclined planes, once drew 223 tons, at 12 miles an hour, from Liverpool to Manchester. Now, 9 tons 17 cwt. X 24= 236 tons, from which deducting 10 tons for the weight of the 23 240 104 1 1 nearly; that 10 240 is, the maximum inclination which a locomotive-engine could ascend without any weight attached, having coupled wheels, and in a medium state of the rails, would be an ascent of about I in 10. This bite varies much with the weather and state of the rails. Generally, the upper surface of the rails is covered with a thin coating, compounded of dust and oxide of iron, presenting in dry weather, that iron glassy appearance which we see where horses have slid about in the London streets; and which, at first view, impresses one with the idea, that such a surface could furnish but little hold for the wheels of the engine. However, in dry weather, the coating is hard and firm; and though I suspect the bite is then not so great, yet as the surface is at the time smoothest, the rolling friction is probably a minimum, which makes up for the difference, and causes the rails to work so well. In very wet weather the coating is perhaps nearly washed off, or so liquified, as to permit the surfaces of the wheel and rail to come into immediate contact. By this means the bite may be somewhat augmented, and probably, the friction too, by the imper ect liquefaction of the coating. These two circumstances combined, may be the cause that in very wet, or very dry_weather, the rails work equally well. But when a little wet has weakened, without destroying, the tenacity of the coating, it will form a series of rollers like grease between the wheel and the rails, thereby diminishing the bite, while yielding to pressure, it will present a continued obstruction to the wheels, and hence increase the rolling friction of the train. In this case, the effective action of the engines will be extremely enervated; and, of course, the velocity of the train considerably impeded. I was informed the trains had, in this way, been occasionally reduced to a stand-still, when ascending the inclined planes. In one instance, I myself saw two engines with seventeen loaded waggons creeping up the Whiston plane, after a little wet, at a rate of scarcely three miles an hour; and if it had not been for two men seated on the front arms of the first engine, dropping sand incessantly on the rails before the engine, it appeared evident to me they could not have gone up at all. I also observed, that the trains invariably travelled much slower, and with more difficulty, early in the morning, before the dew was off, than later in the day. The difference in the time of transit amounted to a quarter of an hour or twenty minutes, though the loads were very nearly the same, and the slower train had the advantage in point of road, that is, in going from Liverpool to Manchester, which is easier than from Manchester to Liverpool. I hope I shall be pardoned for saying so much on this part of the subject; but it is one of such paramount importance in the mechanical operation of railways, that I could not lightly permit it to pass. Next to the improvement of the engines, it demands the deepest attention; for it is lamentable, that a heavy dew, or a little rain which would scarcely lay the dust, or a little snow which would disappear the moment it fell, should be able to paralyze one of the noblest of modern inventions. A remedy, I think it would not be difficult to find. Should I ever be connected with the construction of a new railway, I intend to try one, unless before-hand, a better should be in use. By what has been shown, it is evident that the first principle of locomotion is the hold or bite of the wheels on the road. Unless this exceed the amount of traction force, steam-power is thrown away, the wheels will slide round, and no motion can ensue, or be kept up after it is attained. When the bite is ample and the steam turned on upon a stationary engine, its want of vent rapidly raises the temperature of the boiler, and, consequently, the quantity and pressure of the steam on the piston. A gradually increasing motion is the consequence. But as this motion increases, so do the strokes of the piston and consumption of the steam; and it results, that the temperature of the boiler sinks again, until it has reached that point at which the temperature carried off by the consumed steam, ba lances that communicated by the fire to the boiler. At this point, a uniform motion in the train will commence, and be maintained, without any regard to the bite of the wheels being in excess of the traction of the load. An engine of a less weight will therefore preserve that velocity it could never have given. However, it will, in all cases, be advisable to have more bite than is wanting; especially as the expense of propelling an additional ton or two is immaterial, and might always be made up in the structure of the carriages of the train. Objections I know arise to weighty engines, but where the question is one of efficiency or inefficiency, there is little room for choice. I would much rather increase the strength of the rails, which, wearing but little, will be thrown chiefly on the first cost, than be deficient in that which is indispensable for success, namely, power in the engine. A very important consequence in the structure of a railway follows what we have said, but which has been strangely overlooked in some of the projected railways. I allude to elevating the main, and intermediate termini of a railway, above the general lines in their respec.. tive neighbourhoods, so as to begin with a descent from every point of rest. By this means, gravity may be pressed into service in aiding to get up the full speed quickly with departing trains, while with arriving trains it would be scarcely less beneficial in arresting their velocity. As the engines commonly labour and strain more at starting than in other parts of their course, this is the place at which, on the principle of economy as well as on account of the speed, it will be most advantageous to assist them. On the Liverpool and Manchester line, this object has been pretty well accomplished at the two extremes, but whether by accident or design I am unable to tell. The present number having been extended to a greater length than I intended, I must reserve the mathematical consideration of the subjects just now discussed, to a future communication. Another point, of scarcely inferior importance, also suggests itself from our views of the necessity of having ample bite, namely, that of making all the wheels of the engine efficient, or of applying the steam to them all, instead of to two only, as is commonly done. In some engines the two hind wheels are fixed to the axle, to two cranks of which, in perpendicular planes, are applied rods from the pistons. In others, strong bars also go from each hind, to its corresponding fore wheel; thus tying, or coupling thei together, and making all four do their duty on the road. Among practical men, considerable difference of opinion exists as to the respective merits of these methods. Mr. Dixon and Mr. Roberts, of Manchester, gave me their opinion in favour of uncoupled wheels. Coupled wheels, one of these gentlemen thought not so well adapted for quick work as uncoupled; and both allow, that they are much more likely to get strained, and out of order. On the contrary, others, and among them a gentleman who has several of his engines at work on the Liverpool and Manchester Railway, expressed to me a decided preference for coupled wheels. Mr. Dixon made an observation, which, coming from one of his extensive opportunities of acquiring correct practical knowledge, is deserving attention-he thought that uncoupled wheels have as much power for rapid motion, as, in the present state of our steam-engine skill, steain can be found for. Admitting this, would it not be advisable to reduce the weight of the engine, so as to ease the rails of the great stress on them, and contrive some means of applying the steam to all four wheels without creating that strain which is complained of? Not knowing whether it has been tried, it has occurred to me, that if the fore and hind axles were similarly cranked and coupled, with strong carriers (as Mr. Gurney would call them) on their shoulders, which were made to act against a bolt in the interior circumference of each wheel, the wheels might turn like other carriage-wheels, freely on their axles, and obviate much of the straining of wheels immoveably tied to each other and to the axles, while each would do its portion of the work. Kensington, June, 1835. JOHN HERAPATH, M'CURDY'S PROPELLERS. Sir,-Had Mr. M'Curdy been a little ore explicit in his account of his pro peller, he would have saved both himself and me some trouble, and have prevented any misunderstanding. In his description he does not state that his cranks are to be of cast, and not wrought, iron; and the latter being the material of which they are generally made, it was but reasonable for me to suppose that he followed the usual course. Allowing therefore, the advantage in point of cheapness of cast cranks over wrought, and of "one pattern serving for all,” (vessels of all sizes ?) I have only to observe, that there is quite as much uncertainty in producing a perfect casting, as a perfect welding; and that as wrought iron is flexible and tough, and cast the contrary, (according to Tredgold's experiments, the specific cohesion, taking glass as one, of the best German bar, is 9.880, and of the best German cast, 7.250,) what is wanting in strength, must be made up for in bulk, and consequently weight. Nor has he disproved the inutility of using a number of cranks, which being able to act only in unison, the derangement of one would interrupt the working of the others. If, for instance, the paddle arm or rod B, were to receive an accidental blow or shock, so as to bend it, this would render the action so stiff, as greatly to impede the working, if it did not derange or break the whole appa ratus. He Mr. McCurdy is altogether mistaken in imagining that my remark upon the originality of the invention, was intended as "a sneer;" or that by that remark, I intended to attack the validity of his patent. I did not even know that the invention was patented. does not so state in his description (No. 607). I merely meant to infer that any constant reader of the Magazine would recollect, that paddles on nearly the same principle had been proposed and described several times in it, and that it would be unnecessary for me to repeat such descriptions. I had in view, Chandler's paddles, vol. x. p. 289, and more especially the plan proposed by "Robinson Crusoe," vol. v. p. 201. The principal point in Mr. McCurdy's propeller is, the placing the cranks at different angles, which produces a quick succession of dippings of the paddles; this has been adopted by Stevens-the only difference being that M'Curdy's is a four-throw, and Stevens's a threethrow. I have, it will be perceived, spoken of "Fair Play," as Mr. M'Curdy. Indeed, it must be evident to every one, that the defence of his propellers, was either written by him, or to his dictation. But this does not, in the least, alter the strength of the arguments. I am, Sir, &c. SCRUTATOR MECHANICUS. June, 1835. A WORD OR TWO FOR MR. PINKUS. some Sir, -There is a practice amongst some men who are scientific, or pretend to be so, that cannot be too severely censured. It is this:-whenever a plan in the arts is proposed that bears the stamp of originality, there are persons always ready to pounce upon the project and lay claim to its invention. You will generally find, upon inquiry, that those persons have standing caveats at the patent offices, with cunning titles, suited to any thing they may choose to adapt them to. I have several times, in the course of my practice as an engineer, met with the most glaring instances of fraud of this kind; provision ought to be made against them in any new patent law that may be framed. My attention has been drawn to this subject, by a letter in your 617th number, from Macclesfield, claiming whatever merit there may be in the pneumatic railway. The writer shows by his letter, that he is not well informed on the subject, and that his ideas about getting a power by forcing air through a long pipe, are altogether fallacious. It has long since been proved, that we cannot get power and speed in such manner; the friction would annihilate the whole of the moving force employed. It is well known, however, that when air in a pipe is rarefied, the effect is entirely different. Besides, Mr. Pinkus has a mode, by means of fixed valves, of regulating the length of the column of air, as practice might require. In looking at that gentleman's published specification and diagrams, I see that he understands the subject that he is upon, and has provided the means of carrying his plan into effect. It is true, that Mr. Pinkus must remove all the air before his piston, but then he has not to do that all at once. He does that by keeping up the rarefaction between the valves;-the larger the pipe,. the less the degree of rarefaction of air, -the smaller the pipe, the higher the degree. Within certain limits, the same power would act in both alike Your other correspondents on the pneu matic railway have committed some great errors, which I will, at another time, point out." Now, as to the originality, I happen to know that the principle belongs to Mr. Pinkus, because in the early part of the year 1825, I was employed by that gentleman to make a perspective and sectional drawings of a plan for propelling, which he proposed by means of a pipe to be laid along a railroad, and by the side of a canal, through which he intended to pass a current of STEAM, instead of air. The pipe had a narrow slit or opening on the side or under side, which was closed by a flex-ible valve, acting from the inner side,. and which was closed by a wheel, and kept tight by the pressure of steam :: the pipe had a jacket through which: hot water or steam was to circulate, so as to prevent the steam in the pipe from condensing. The steam was to be let in at every mile or two along the line, from boilers or steam generators. This was certainly a pretty idea, but I know that the inventor was the first to point. out its fallacy, on the ground of the impossibility of getting a power either by forcing steam or AIR into, or through a long pipe, because the greater the pressure of the steam or compression of the air, the greater the friction and retarding force; to say nothing of the great loss from constant radiation of heat, condensation of the steam, and vast quantity required. Moreover all the joints must be tight, in proportion to the pressure, or the loss would be We shall be happy to hear again from our correspondent, and hope he will then show a little more clearly than he has done here, how Mr. Pinkus has actually "provided the means of carrying his plan into effect." We do not, of course, refer to the pecuniary, but the scientific means.-ED. M. M. great in proportion to such pressure. So much for the originality of your Macclesfield correspondent. Mr. Pinkus began his patent for the pneumatic railway in 1831, as I see by a notice from the patent-office now before me. I shall be glad to see this statement printed in your Magazine, to which I have been a subscriber some years, in the usual fair manner in which you print the pro's and con's. Your obedient servant, Chatham, June 13th, 1835. THE BUTTERLEY COMPANY AND HOTAIR SMELTING PROCESS. Sir, I have to request you will correct an error in No. 614 of the Mechanics' Magazine, in which the Birtly Iron Works, near Newcastle, are confounded with the establishment of the Butterley Company, who are proprietors of the Butterley and Codnor Park Iron Works, Derbyshire. This company has been formed for half a century, and possesses an almost inexhaustible field of the finest minerals. Coals they send off in large quantities for sale in all directions, by the various inland navigations, communicating with the Trent, the Soar, &c. &c., untill it meets the sea-borne coal; and at least ten different beds of iron ore, all lying in the immediate vicinity of the furnaces, are now in work for their supply. The Butterley Company employ in their mines, coal-fields, blast-furnaces, rolling-mills, forges, boring-mills, and steam-engine manufactory, 35 steamengines of all sizes, from 80 inches of diameter of cylinder, and have six blast-furnaces, of which four are now in work. The whole of these furnaces are blown with heated air, and the coal, which is admirably adapted for the purpose, needs no cokery, being very carbonaceous. The mountain limestone, which lies but three miles from the furnace, is used as flux for the ore, which is clay ironstone. These materials produce a very fine grained castiron, remarkably soft and fluid, and atthe same time, they are equally well adapted to make "forge pigs," from which are manufactured bars, hoops, and boiler plates, of the best quality, and steam-engines. But, as your correspondent observes, that much prejudice exist against iron made from heated air, I shall have much pleasure in sending you specimens of the iron, both wrought and cast for inspection. M. Dufresnoy, M: Perdonnet, and several other Frenchmen of scientific reputation, have visited the Butterley Company's Works, with which they have been highly pleased, and have been willing to communicate the valuable information they possess, in return for such as was afforded them here. I am, Sir, Your most obedient servant, Butterley Iron Works, near Derby, (Abridged from the Journal of the Franklin Institute.) 1. Woodside's Revolving Harrow and Seed Cart. The committee having examined a model of the machine, and inspected numerous certificates of its performance, which have been given by agricultural gentlemen, are of opinion that this is a valuable improvement in that necessary implement of husbandry, the harrow. Some of the committee were present during a trial of one of these machines, the result of which was highly satisfactory. It seemed on that occasion to require more power to move it than the common harrow; but its superior efficacy in eradicating weeds, and pulverizing the soil, will, it is believed, more than compensate for this difference, as it will certainly do more work at one operation, than the common harrow will at two or three. Another advantage which it possesses, is, that it is not so liable to be clogged or choked by weeds, and clods of earth, as the common harrow. These are collected by the latter; and wherever the harrow is raised to clear it of them, there remains a heap of rubbish, which impairs the evenness of the field, and injures the crop. The committee have not had an oppor➡ |