AXLE, a pin or shaft on which a wheel turns, or a shaft revolving in bearings, and having wheels affixed. In carriages and carts the fixed bar is called the axle-tree, and the ends are the axles. In railway carriages, wagons, locomotives, tramcars, travel ling cranes, and the like the axle runs in bearings, the length mak ing contact therein being called the journal. Axles for steam and internal-combustion engines which require outside connecting-rods or coupling-rods have the journals between the wheels, but other rolling-stock and tramcars outside. (In M.E. axel-tre is derived from O.Norw. oxull-tre, cognate with O.E. aexe or eaxe, and Lat. axis.) An axle may be driven, as in the case of locomotives, tramcars, or cranes, either directly or through the intervention of gearing, or it may be idle in this respect. Motor-car axles comprise two main classes, the driven one at the back in two parts with differ ential gear, and mounted within a tube or secondary axle, and the front one consisting of a fixed bar, to which are pivoted the stub axles. Ball or roller bearings take the place of plain bearings in motor and certain other axles, but while roller bearings have been applied to some extent in railway carriages, the plain axle-box still holds sway. The latter only requires bearing surface over the top half of the axle, hence merely a "keep" is fitted to the bottom half. The bearing surface is usually gunmetal, with white-metal liners cast in, and adequate arrangements for grease or oil lubrication have to be ensured. In view of the serious consequences likely to arise from broken axles on railways, only the best class of steel is employed, made and tested to stringent specifications. The large numbers required entail the use of special lathes, turning both journals simultaneously. Finally a hardened steel roller in a holder is pressed with great force against each revolving journal, closing the pores of the metal, and leaving a highly-burnished and hard-wearing surface.
The failure of a locomotive crank-axle is even more serious than that of a carriage or wagon, consequently the manufacture demands the utmost care. In some cases a solid forging is sup planted in favour of the "marine type" built-up axle, made of heat-treated hollow axle, crankpins, and web shrunk together, and locked with screws. Mr. C. B. Collett follows this method for Great Western engines, of the "King" class (see fig.). Wheels are forced on their axle seatings in hydraulic presses, the pressure required varying from 8o tons in the case of small wheels up to zoo tons or more for large locomotive driving wheels. For the final processes of turning the treads, the axles are put in the lathe with the wheels thus assembled. (F. H.) A X-L E S-T H E R M E S, a watering place of south-west France, in the department of Ariege, at the confluence of the Ariege, with three tributaries, 26m. south south-east of Foix by rail. Pop. 1,13o. Ax (aquae), a spa of ancient (Roman) origin, is well known for its warm sulphur springs, which vary greatly in temperature.