One of the chief difficulties in the application of locomotive carriages to railways has been to obtain sufficient friction or adhesion between the driving wheels and the rails to cause them to ascend planes of considerable inclination, as the wheels are in such cases apt to be turned round without advancing the carriage. To prevent this, Messrs. Vignoles and Ericsson, by their patent of 1830, proposed to introduce a third or friction rail between the two bearing rails. This friction rail consists of a flat piece of iron extending along the middle of the road, and securely fixed in a vertical position, as represented in section in the annexed figure. On each side of this friction rail, which is made of considerable depth, is placed a horizontal friction roller, as shown at c, d; the roller c being made considerably larger than d, and fixed upon its vertical shaft e, while d is permitted to turn freely on its vertical shaft f. On the driving axis g is fixed a bevel wheel h, which turns another bevel wheel i, fixed upon the vertical shaft e of the driving roller c.
The bearings of this driving roller and its shaft are firmly fixed to the under ride of the locomotive carriage by the block shown at k, and the bearings of the friction roller d are ninged to the block at l, that it may at pleasure be pressed against the friction rail a, by the lever m. This lever is wrought by bringing it within reach of the engineer or his assistant, who, acting upon the long arm of a powerful lever, causes any degree of pressure upon the friction rail by nipping it between the rollers c, d; at the same time the driving wheels n and o of the carriage are released, and permitted to turn independently of the driving axis g, by shifting the binding rings p, q. When the friction driving apparatus is in action, the wheels n and o become simply supporting wheels and run on the supporting rails r,r- "The patentees confine their claim to the driving apparatus which we have described, though they state that it. may be put in motion through the medium of the driving axis, by the steam engine employed to actuate the driving wheels of the usual construction, or a separate cylinder may be employed to give motion to the patent driving apparatus.
The depth of the friction rail a must necessarily be varied to correspond with the inclination of the steepest plane on which it is to be applied.
There is evidently considerable ingenuity displayed in these arrangements: but we doubt whether the patentees have hit upon the readiest way of obtaining an increase of adhesion by an increase of the surface, and pressure of the moveable and stationary parts in contact.