The pivot, or centre, upon which a carriage wheel turns. They were formerly made of wood, and, we believe, are to this day, in some parts of the country, but are now generally constructed of iron. Numerous improvements have, of late years, been introduced in their construction, some of which we shall notice, after a few words upon their more ancient construction. One very old plan was to fix the axle immovably into the naves of both wheels, the axle revolving in bearings attached to the carriage; by this means the nave was less weakened, and the wheels had less play, than if the axle-tree was fixed to the carnage, and worked in a box in the nave, but were inconvenient in turning, as both wheels revolved with the same speed; the axle-trees were, therefore, attached to the carriage, and each wheel revolved separately upon its axle, by which means, in turning short, the inner wheel could remain stationary, and serve as the centre of motion to the carriage. Axles were originally made straight, their arms lying in the same horizontal plane, and the wheels, of course, perpendicular to them; but as carriages came more generally into use, more room was required; and the roads being narrow and bad, and the wheels being, therefore, required to keep in the beaten track, recourse was had to splaying the wheels, by bending the axles downwards, by which means the upper part of the rims of the wheels were further apart than the lower; and this method continues in general use to this day, although the improved state of the roads no longer requires it, and the draft is made heavier, and the roads more quickly destroyed by it.

The objects chiefly aimed at in the various improvements in axle-trees, is to diminish the friction by decreasing the amount of rubbing surface, and by carefully excluding dirt from the boxes; in keeping them well oiled, and to attach the wheel so securely as to avoid the fatal consequences arising from the linch pin falling out We shall now proceed to describe two constructions of axle-trees, invented by Mr. Mason, of Margaret Street, Cavendish Square; the first adapted to what are commonly called Collinge's, or patent axles; and the second, to the description of axles called mail-coach axles. The first construction is shown in Figs. 1, 2, 3, and 4.

Fig.1

Axle Tree 100

Fig.2.

Axle Tree 101

Fig3.

Axle Tree 102

Fig. 4

Axle Tree 103

Fig. 1 represents a perspective view of the axle, with its principal appendages arranged in a line to show the mode of their application. Fig. 4 represents a longitudinal section of the axle-tree, with its several appendages screwed up into their respective places, and lying inclosed in the box peculiarly constructed for that purpose. Figs. 3 and 4 give sections of certain parts of the axle-tree and box, hereafter to be described. The like letters refer to similar parts in each figure, a a, the main part of the axle-tree; b, a fixed shoulder; c, a movable shoulder formed upon a metal collet, and rendered capable of being slided backwards and forwards, but not of turning round. This collet is adjusted and retained in any required situation, as will be presently shown; d is a screw formed upon the outer end of the axle-tree; e is a nut, hexagonal on the outside, and screwed in the inside to fit d. Around the inside of the hexagonal nut are cut longitudinal, and at equal distances, six semicircular grooves (as partly shown in Fig. 1), but more distinctly seen in the section 'Fig. 2; the screw d has, likewise, two similar grooves cut into its thread, and so placed with regard to each other, that when one groove corresponds with one of the grooves in the nut, the other groove shall be midway between two other grooves in the nut; and, in order to fix this nut in the required position, a cylindrical pin, which is rivetted to the hexagonal plate f, is inserted into one of the holes formed by the union of a groove in the nut with a groove on the axle, which entirely prevents any rotation of the nut so long as the pin remains in the hole; and there being two grooves in the axle, and six in the nut, the position of the nut may be regulated to 1/12 of a turn, equal to 1/120 of an inch, if the screw has 10 threads per inch.

To prevent this pin coming out, a collar of leather g is first put on the long hexagonal-headed screw h, when the latter being screwed into the internal screw of the axle-tree (seen at Figs. 2 and 4), the whole is thus made fast. Having thus described the construction of the axle-tree, it remains for us to explain the construction of the box, which we have put in section in its proper place, around the axle-tree in Fig. 4. k k k k show the cylindrical parts of the box, with a cap f f screwed on its outer extremity, which serves to contain oil for those parts of the axle-tree which are contiguous, o o are long grooves also for oil; two of these are brought into view in the longitudinal section, Fig. 4; but there are four of them, as may be seen in the transverse section at Fig. 3, which section is made where the dotted line divides Fig. 4. p p is another reservoir for oil. The whole of the arrangements in this invention appear to us excellent. The quantity of oil contained in the reservoirs, and which is constantly circulating round the axle, is greater than in any other wheel-box that we recollect, and must greatly reduce the friction.

The ease and safety with which the wheel may be let out when travelling on bad roads, is another great advantage, and which we believe to be peculiar to this axle, whilst the method of securing the wheel upon the axle seems to leave nothing to be desired on that head. This last part of the invention may be also usefully employed in various parts of machinery, as where wheels run upon studs, or pivots, etc. The figure beneath represents Mr. Mason's improved mail axles, although some parts of the invention are applicable to the patent axles. a is the box cap, which constitutes at the same time an oil cup with a conical end c, which fits into the conical part g of the axle f; when that is fitted into the box e and the cup screwed into d, the oil then flows through an aperture in the end of the cup c into the hollow part of the axle, and passes out to the box at an aperture h, supplying the long reservoirs in the interior of the box. There is, likewise, a very small groove cut longitudinally on the axle, extending both ways from h, so that the oil may be readily distributed over all the bearing parts.