CAUSES OF OSCILLATION ON THE GREAT SOUTHERN RAILWAY.

Press, Volume XIX, Issue 2817, 13 May 1872, Page 3

CAUSES OF OSCILLATION ON THE GREAT SOUTHERN RAILWAY.

TO THE EDITOR OF THE PRESS. Sir, —I see by the reports of the debates in the Council that Mr Tosswill called attention to what he said was the "alarming rocking" of the carriages on the Great Southern railway. As perhaps many of your readers may be needlessly alarmed by not knowing the causes of this oscillation, I think it will not be out of place in mc to give the reasons why the carriages run unsteady. Many of your readers are no doubt aware that between Selwyn and Lyttelton. the rails are of two different patterns; the Christchurch and Lyttelton railway having been constructed with round-headed rails, ami the Great Southern line with flatheaded rails. First, with regard to the rails on the Great Southern line. I may remind your readers that the tires of all the railway wheels are formed of a conical shape, and that the flat-headed rails are fixed into the sleepers to a slope, so as to fit the conical shape of the wheel. Your readers must understand, however, that it is practically impossible to slope the rails with such mathematical accuracy as to tit the tires of the wheels, but there is still a greater impossibility in preventing the settling of the rails in their beds, or the sinking of the sleepers in the ballast. The slightest settlement or sinking, in either case, would prevent the flat-headed rails from coinciding with the tires of the wheel. As the flatheaded rail measures about inches in width, and when one bed of the rail does not exactly fit the conical shape of the tire of the wheel, it follows that either the large or small side of the conical-shaped tire must be running on one edge or the other of the flatheaded rail. One wheel is therefore running with a greater circumference than the other, consequently the smallest settlement in the level of the rail in its bed, or the sleeper in the ballast, causes the train to oscillate to one side or the other, as often as the least inequalities in

the levels of the line occur. For these reasons the flat-headed raiis are univer?.iUy condemned. The Great Southern railway, witli its H»t-headed rails, was laid to a gauge three-eighths of an inch broader than the Lyttelton and Christchurch railway, and it must therefore follow as a natural consequence that thc sinuous motion must be so much greater. I will now endeavor to point out to your readers the reasons why the carriages run more smoothly on tho Lyttelton aud Christchurch railway than they do on the| Southern _inc. The head of the rail used in the former is rounded with a curve equal to a 12-inch radius, and as there is only a £-inch of lateral play allowed between the gauge of the wheels and the gauge of the rails, your readers will understand that thc conical - shaped tire can only vary to that extent, namely, J-inch allowed for play, while the flat-headed rail, being 2.} in wide on the top, and when in the slightest degree out of adjustment, can vary on thc conical tire (including the additional play allowed on tlie Great Southern line.) 3-gin. As the conical shape of the tire is upon a slope of 1 in 20, and when one wheel is running on one rail on its largest circumference, and the other wheel on thc other rail on that part of the tire near its smallest circumference, it follows that in every revolution the one is inclined to get close upon J-inch in advance of the other. This, I think, satisfactorily proves the cause of the greater oscillation on the one line than on the other. What makes this matter worse is, that while the same carriages are obliged to run on both kinds of rails, it prevents the tires from wearing themselves to suit the shape of either pattern of rail. If a carriage had been running for a length of time on the Lyttelton and Christchuroh line, and then removed to the Great Southern Railway, the oscillation would be still more perceptible. As this subject is very difficult to be made clear to your readers by mere description, without diagrams, I would refer those who have got access to the book, to Clark's admirable treatise on railway machinery, chapter vi., page ISO, where diagrams and full particulars will be found, which, I think, will bear out my assertion. I am. Sec, Plate-Layer. Christchurch, May 11, 1872.