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106 THE CIVIL ENGINEER AND ARCHITECT’S JOURNAL. [April 1, 18CS. borne in mind “that when an engine was running, especially upon inclines, there were many circumstances to increase the weight on the driving-wheels. The draught through the draw-bar tended to lift tho engine from the front wheels, and thus to increase the load on the driving-wheels. In going up an incline, the water rose at the back end of the boiler ; the difference of level upon an incline of 1 in 10, being 19 inches in the ordinary length; and the base of the centre of gravity was thrown further back upon the driving-wheels.” And that “ These circumstances materially affected the running condition of the engine.” The explanation suggested of the apparent paradox of an effective adhesion being obtained, exceeding that due to the coefficient of friction, appeared altogether insufficient. Mr. Colburn said that, “ if the engine was making steam freely, and blowing off strongly, the re action of the escaping steam against the air sensibly increased the weight of tho engine. An engine would scarcely be blowing off steam while dragging a load up 1 in 10. Tho steam escaping from the blast pipe might indeed have some effect in the direction indicated, but not a very material one. A more usual explanation of the anomaly alleged was, that by the partial sinking of the wheel into the rail (clue to the concentrated pressure of the former) at its point of contact, and the elasticity of the material, the wheel obtained a greater grip on the rail than what would be due to friction alone. But this explanation cut both ways; for such partial yielding would necessarily augment the re sistance in front, by raising a steeper gradient, so to speak, in front of the wheel. The interposition of sharp sand would, of course, increase the effective adhesion ; but as such increment of adhesion could only be obtained at the expense of the structure of the rail, it would not be desirable to rely on the use of sand in ordinary working conditions, He believed that any engine, having all its wheels motors, might in dry weather exert a tractive force of £th of its weight, and by the use of sharp silicious sand, might do so in all weathers; but that to obtain a higher effective adhesion than that due to the coefficient of friction was as impossible, as to utilise more than 100 per cent, of tho entire theoretic duty of a fall of water. In laying out a mountain line, on which sharp curves were inevitable, it was always desirable to allow for the increased resistance on such curves, by flattening the gradient where they occurred, and thus to equalise the draught on all portions of the ascent. But unfortunately, in attempting this, Engineers had hitherto worked very much in the dark, owing to the want of authentic experiments on the increment of resistance due to curves of different radii at varying speeds, with engines and*carriages of a given wheel base. It was strange that a series of experiments, admitting of such easy execution as these do, should not yet have been instituted, to determine a matter so important in mountain railway making. Mr. Latrobe, the Engineer of the Alleghany Mountain Lines de scribed in Mr. Isaac’s Paper, published in America many years ago, the following Table of such resistances, stated to have been founded on experiments on a level:— Table showing the Resistance due to Curves. By Mr. Latrobe. Radius Resistance is in Equivalent to that of Chains. an Ascent of— 40 1 in 1,949 35 1 in 1,747 30 1 in 1,448 25 1 in 1,236 20 1 in 993 15 lin 734 10 1 in 482 8 lin 389 5 1 in 248 3 1 in 149 But Mr. Conybeare had found in practice, that the relaxation in gra dient prescribed by this table was wholly insufficient to counteract the increase of resistance occasioned by curvature on steep gradients. It appeared, too, that in American practice this table had been found altogether insufficient. In Mr. Isaac’s Paper, it was stated that, on the Mountain Top Incline, the gradient was reduced on curves of 300 feet radius, from 1 in 18-87 to 1 in 22 22; and that the relaxation of gra dients on such curves (based on Mr. . Latrobe’s table) was, over the Board Tree Tunnel, 31 feet a mile. This being found insufficient, it was increased on one part of the Mountain Top Incline to 43 feet per mile, and on another portion to 58 feet per mile, and yet even then was found to be insufficient. t “ The speed was always diminished on leaving a straight portion of the track, and on entering a curve of minimum radius, although the resistance of gravity, on the latter, was 25 j lbs.per ton less than on the former; a fact evidently proving that the resistance of the curve must have exceeded 25} lbs. per ton of engine and train. It is probable, that Mr. Latrobe’s experiments give a sufficiently approximate measurement of the increase of friction of the curves, duo to carriages of American con struction. Assuming, therefore, his allowance of 13 lbs. per ton, as the additional friction of the train, on a curve of 300 feet radius, the addi ¬ tional friction of the engine, due to such a curve, must have exceeded 49 lbs. per ton of its own weight. This friction will of course vary in engines of different construction.” On the American lines the amount of relief, required in the gradient in going roun 1 curves, thus appeared to be underrated ; but on the Mont Cenis line it evidently had been overrated, as regarded the engine’s gross speed on the curves. Perhaps Captain Tyler would state the amount of relief given ? It was desirable that a question of such importance as this should be determined by a series of carefully-insti tuted experiments. He considered the Cymbeline class as a good type of engine, for working steep gradients with economy, as any in England. It would be an improvement to adopt the American plan, of having four pairs of wheels coupled; and as such engines were used in the United States on curves of much sharper radius than those usual on English lines, there would appear to be no objection to the addition of a fourth pair of wheels on that head. If tank-engines were objected to, the wheels of the tinder must be made driving-wheels, either by some system of coupling or by supplemental steam cylinders attached to the tender : the last plan involved a great loss of heat. The sharpest curve he had ever met with was one close to the town of Rhymney, on a mineral line, called the Old Rhmney, which he had converted into a passenger line. This curve he had ascertained, by two measurements, to be 1J chain radius. The line was worked by tank engines, having six wheels coupled, with a wheel base of 11 feet 6 inches, which ground round it at the rate of 3 miles or 4 miles an hour only. The curve by which the Great Northern joined the Metro politan Railway was 7J chains radius, on a gradient of 1 in 46 ; and the North Western had this year deposited plans for an extension to Dowlais, which joined the Brecon and Merthyr at that place, with a curve of 7» chains on 1 in 40. He thought that at present there was a disposition to underrate the objection to such curves as these. The results of experiments had proved, that the employment of a single engine, as on the Semmering, gave better results than were ob tained by two engines coupled together, as on the Giovi. Mr. Fairlie’s plan had all the disadvantages of the Giovi, with the addition of some grave disadvantages peculiar to itself. When tried on the Brecon and Neath line, it had turned out a complete failure, as any expert might have predicted. There was one fire-box to the two engines, thus the escaping products of combustion had two lines of exit to choose between; and it was a fact well known to all who had experience in boiler work, that the products of combustion, on leaving the furnace, took the shortest and hottest path open to them on their way to the chimney ; bifurcated flues were, therefore, erroneous in principle. The steam-pipes were always breaking ; the driver could not see the state of the fire; and both driver and stoker were without protection from the weather. The great length of the boiler was also objectionable on steep inclines, as it threw too much weight on the trailing-wheels. In a pamphlet published in 1859, after describing the lines by which the Alleghany mountain had been traversed, he wrote— “Why should not similar expedients be adopted at the passes of the Alps, which still continue to occasion so inconvenient a break in the railway communications of Europe ? It has often been proposed to traverse three of these passes by railways; one of which has actually been commenced (though grave doubts are entertained of its being pro ceeded with), and a large engineering expenditure has been incurred on the plans and surveys of all three projects, eachjof which would involve at least one tunnel of unprecedented length and difficulty; but these passes are already traversed by roads which do not exceed in inclina tion the railway zigzags over the Alleghanies; and the alteration of the existing roads at Mont Genis and the Simplon into railways of this class would be an improvement of European importance, and one that could not fail to prove remunerative to any company or government that would undertake the work.” Mr. C. H. Gregory, V.P., said, Mr. Conybeare had alluded to the variations in the estimates of the amount of retardation arising from curves; but he had omitted to mention one circumstance which would account for the difference, viz., the structure of the engine. With engines having a long wheel base, and rigidly parallel axles, serious retardation was unavoidable on sharp curves; but the use of bogies, radiating axles, and other appliances, had already greatly diminished the resistance arising from curves, and further improvements might be anticipated in the same direction. He would call attention to some local difficulties which would affect the working of a railway over the Mont Cenis, in regard to which Mr. Brunlees would perhaps give some explanations. During four or five months of the year, the district extending from Lanslebourg over the summit of the pass to Molaret (a village about half-way from the summit to Susa), was covered with deep snow, and the wind frequently formed deep and extensive snow-drifts, varying in extent and position with the force and direction of the wind. During that period the traffic was carried on between the places named in sledges ; and those who had travelled by that route would confirm the observations he had made, that, without any long warning, the sledges often came to very deep snow-drifts, through which their progress was slow, and from which, at times they had to be dug out. Besides the drifts, there