A very ingenious proposition for making use of the power of a horse, moving at his slow working pace, to communicate a high velocity to carriages upon a railway, through the medium of a new arrangement of pulleys and ropes, was invented by Mr. Joseph Saxton, of London, for which he obtained a patent, on the 20th June, 1833. The invention consists in the application of pulleys of different diameters, termed differential pulleys;" the principle of the action of which will be comprehended by the following illustration: pulleys, it would be propelled from g to j, by the endless rope c d being moved the much smaller distance of h to i, indicated by the dotted lines; and these distances will be as 13 to 1.

Fig. 1 (in the opposite page) represents a combination of two pulleys, their diameters being as 6 to 7; a being the larger pulley, and b the smaller one; c d is an endless rope, passing over the sheaves e e; the part c of the endless rope first takes a turn round the larger pulley a, and the part d also takes a turn round the smaller pulley b. If then the rope d be moved in the direction of the upper arrow, it will draw the lower part of the pulley b in the same direction; meanwhile, the part c of the endless rope will be moving in the direction of the lower arrow, and will move the lower part of the pulley a in the same direction with this part of the rope; consequently, the two pulleys a b (which are fixed together) would turn on the mean point f, as a fulcrum: g is the centre of the two pulleys. Let it then be supposed, that the part d of the endless rope be moved from h to i, it will be evident that the centre g of the differential pulleys a b would be moved to the point ,j, and, consequently, if any object were connected to the centre g of those differential Fig. 2 represents the contrivance applied to an ordinary carriage, having four wheels, as usual, two of which, k k, are shown, a and b are the differential pulleys, placed on an axis g (see Fig. 3); m is a frame which carries the differential pulleys, and turns in bearings n n, affixed to the carriage.

The projecting arm m is forked at the outer end, as shown in Figs. 2 and 3, at o o; and the forked ends serve as bearings to the axle g of the differential pulleys, the pulley a being permanently fixed to the axle g, whilst the pulley b is capable of turning loosely on this axis, when it is not retained by the pin q, which locks the two pulleys a and b together at the times required. By disconnecting these pulleys, the power will no longer tend to drive the carriage. R (Fig. 2) is a lever, turning on a fulcrum S: the upper end of this lever is formed into a handle, and placed under the control of a person sitting in front of the carriage; the other end of this lever receives the flanch of a sliding socket l within it, as shown in Fig. 2; u is a bent lever, having its fulcrum at v, on the forked frame o, as shown in Fig. 3. One end of this cranked lever u has a crotch, which receives the flanch l of the sliding socket; and the other end of the lever u has also a crotch to slide the socket to, on the axis g, backwards and forwards, x is an arm, fixed to the sliding socket w, and carrying the pin q, by which the wheels b are fastened together: a spiral spring is placed on the pin q, to force

Fig.1.

Saxton s Differential Pulley 417

Fig. 2.

Saxton s Differential Pulley 418

Fig. 3 it in, when a part of the pulley which is cut away comes opposite to the bolt; there is also a spring to prevent a sudden concussion. In Fig 2, c a is an endless rope, the part c taking a turn round the pulley a, and the part d taking a turn round the pulley b, as described in Fig. 1. This endless rope is supported, at proper intervals of the road, on sheaves, and passes round a rigger at each end, to which is attached an apparatus for preserving it sufficiently "tight. Now suppose the pin q to be passed through the two pulleys a b, to retain them together, and the endless rope d be moved in the direction of the arrow, a similar action will take place to that described in Fig. 1; that is, the carriage (being attached to the centre g of the differential pulleys a and b) will be propelled forward on a railway with a much greater velocity than the rope travels; and the distance so travelled by the carriage, in comparison with that through which the rope moves, will depend on the differences of the diameters of the pulleys a b; and the nearer the respective diameters of the pulleys approach each other, the greater will be the relative velocity the carriage will travel, to the velocity with which the rope moves.

In order to prevent the two parts of the rope rubbing against each other, in leading on and off the differential pulleys, the axis g of these pulleys is placed at an angle a little varying from a right angle with the direction of the motion of the carriage.

Saxton s Differential Pulley 419

Fig. 4.

Saxton s Differential Pulley 420

Fig. 5.

Saxton s Differential Pulley 421

Figs. 4 and 5 show two different applications of the invention from that shown in Fig. 2; for in these instances there is only one pulley, whilst the two front or two back wheels of the carriage act the part of the other pulley. In Fig. 4, a is one of the front wheels of the carriage, which also acts as the larger pulley; b is the smaller pulley, and is the only one around which the rope c d passes; the wheels a, and the pulley b, being on the same axis g, which runs from side to side of the carriage, and turns in bearings affixed to the carriage. In this arrangement the point f, at which the wheels touch the rail, becomes the fulcrum on which the wheel a turns; and it will thus be evident that if the rope c d be drawn forward in the direction of the arrow, a similar effect will be produced as described in Fig. 2, and as shown in dotted lines in Fig. 4. Nevertheless, if the wheels and pulleys a and b be of the same relative diameters as those in Fig. 2, the carriage at Fig. 4 would only be propelled at the velocity of seven to one, owing to the fulcrum, at which the wheels a turn, being removed from the mean pointf, Fig. 2, between the two diameters, and placed at the extreme end of a radiating line, drawn from the centre of the wheel a to the point at which it touches the railway.

In Fig. 5 the rope is passed around the pulley a, which is the larger, whilst the carriage-wheels act the part of the smaller pulley b, the pulley a and the wheels b being on the same axis g. In order that the pulleys in this arrangement may stand at an angle for clearing the rope, the axle g is formed of three parts, connected by universal joints; and one of the wheels b thus travels a little forwarder than the other, and thus the rope will clear itself. And it should be observed, that in both these arrangements, the pulley around which the rope passes is to be made capable of being disconnected from revolving with the axle as described in Figs. 2 and 3. In the arrangement, Fig. 5, the fulcrum f, on which the wheels turn, is the point at which the wheel b touches the rail or road; and the difference in the arrangements, Figs. 4 and 5, is, that the power in Fig. 4 is applied by the rope between the fulcrumf, and the centre g, of the wheels or pulley a b, where the weight to be drawn is attached: whilst in Fig. 5, the fulcrum is between the centre of the pulley and wheels a; consequently, the arrangements differ in the order of leverage, and, in this instance, will he as six to one.

In these two last arrangements, the rope c d may be either an endless rope, as described in Figs. 1 and 2, or the rope may be single, and, taking a turn around the pulley a or b, is to be wound on a drum at each end of the distance which is to be run by one length of a rope.