The extraordinary friction and resistance between the flanges of the wheels of a locomotive engine, and the edges of the rails, in passing round curves, unless the radii be very considerable, struck forcibly the attention of Mr. Robert Stephenson, who succeeded in devising a very ingenious mode of obviating it, which lie patented on the 23d of January, 1826. The following description of it is extracted from the Register of Arts :—" Instead of two wheels, fixed as usual to the extremities of one axletree, Mr. Stephenson's plan is to have a separate axletree to each wheel, so that they may revolve independently, and at different velocities, as circumstances may require. The outer wheels of a four wheeled carriage (or those which are on the longest of two curved parallel lines) will therefore he at liberty to run faster than those on the inner side (or on the shortest line), thereby preventing that sliding motion, and its destructive effects, when passing round curves, which, on extensive lines of road, are gene rally found unavoidable.
Mr. Stephenson's improvements in axles likewise embrace another object of more momentous importance, that of providing a remedy for the unequal strain to whieh a carriage is subjected in passing over those parts of a railway that lie hollow, or below the level of the contiguous parts, owing to the sleepers or other supports having sunk or given way, which causes the carriage and its load sometimes to rest upon three wheels instead of four, producing undue strains or fractures, and at other times causing the carriage to pass off the rails. To provide against these circumstances, the axletree of each wheel turns in a fixed bearing, which is bolted to the frame of a carriage : this bearing, instead of having a circular aperture for the axle to turn in, has a long vertical slot, in which the axle can rise up and down, as may suit the undulations or imperfec tions of the line of rail. This, however, could not take place, unless the opposite extremity of the axletree moved upon a universal joint, which Mr. Stephenson has adopted, giving the preference to the ball and socket for that purpose, on account of its strength and simplicity. Fig. 1 exhibits a plan of a carnage frame, with its wheels and axletrees ; and Fig. 2 a side elevation or section, as seen from the interior of the frame. Similar letters of reference in each figure indicate corresponding parts: a a shows the frame of the carriage ; bc b c the four tapered aidetrees, having at the small end of each a globular knob, revolving in a hollow spherical socket, as seen at e e e e. In Fig. 2 the bearings f f are shown bolted to the carriage-frame a • at g, the axletree is seen in the upper part of the bearing ; and at h, the axletree is shown to have fallen down the slot, allowing the wheel to accommodate itself to the sunken part of the rail i.
In this last contrivance the wheel alone is supported, and the carriage has still to sustain the unequal pressure, owing to its resting upon three wheels. The chief advantage that results from it, is in keeping the wheel always on the rail ; because, if the hollow was so great as to allow the fianch to rise above the surface of the rail, the carriage might in its progress be thrown over, pro ducing very serious consequences. An accident of this kind recently occurred to the new locomotive carriage of Messrs. Braithwaite and Ericsson (the " William the Fourth "), on the Manchester and Liverpool railway, by which it was very nearly thrown down a deep precipice ' • proving the necessity of some contrivance to effect the object aimed at by Mr.Stephenson's arrangement.
A plan for crossing over rivers and valleys, was patented in March, 1826, by Mr. Robert Midgeley, of Hosforth, near Leeds. The specification does not explain the arrangement designed very clearly, and there are no drawings to assist the understanding ; but as far as we do comprehend it, it bears a close analogy to a plan publicly proposed many years prior, and much talked of at the time, for crossing the river Thames, near to the site of the present South wark bridge. The patentee's proposition, we understand to be this An elevated platform or car, surrounded with railing, supported upon legs, and strongly braced in diagonal directions is to be constructed. This lofty car is to be provided with wheels underneath, which are to run in a double railway laid in the bed of the river, or on the surface of a valley, for the transportation of and goods : thus constituting a sort of travelling bridge, which is to be drawn across by a rope or chain affixed to the opposite shores, in such a manner as to offer no obstruction to craft. It is to be worked by a windlass, either on shore, or on board.
By another modification, it is that the railway shall have a toothed rack, into which a pinion on the framing of the machine is to take, and be worked by a suitable power on board the machine. The top of the machine is i to correspond with the level of the landing places ; and in order that this machine may not be obstructed in its passage, by the gathering of weeds, mud, and other things upon the railway, a lund of plough is placed in front, which is designed to cut them through, or turn them aside as it proceeds.