THE TRICYCLE, as its name implies, is a three-wheeled machine, each one of which wheels must be free to move in its own direction, independent of the united action of the other two. For running in a straight line, all three wheels must be parallel ; while for running round a curve, one or inure of the wheels must be turned until the center lines of the axles intersect in plan, their point of intersection being the center of the curve round which the machine will then run; therefore, the more acute the angle of intersection. the greater will be the radius of the curve; and, inversely, the more obtuse the angle, the sharper will be the curve. Besides being independent in the direction of running, each wheel must also be capable of revolving at a greater or less speed than the others. It is also essential that the greater part of the rider's weight shall be on the driving wheel or wheels, and that. only enough shall be on the steering wheels or wheel for insuring their proper action. Owing to the variety of ways in which these principles can be carried out practically, it is easy to account for the variety of tricycles constructed.
The simplest form of tricycle is obviously that, with only one driving-wheel, either or both of the others being used for steering. An early type of single driver, now practically obsolete, had two large wheels mounted opposite and panillel to each other. one of which was driven, and the other was allowed to run free ; the third, or steering wheel was placed centrally in the rear.
Another form of single driver has the large driving-wheel on one side, and two small steering-wheels on the opposite side, placed respectively fore and aft of the driver, and ar ranged to turn together, but in contrary directions. The double steering, fore and aft, of the driving-wheel overcomes the tendency of the machine to run in a curve, in consequence of the single driving-wheel on one side. This was one of the first tricycles introduced, and has stood the test of competition, being at the present time one of the most popular. Its chief features are that, it is simple in construction, makes only two tracks when running. and is narrow in Width, Its although rendering iL somewhat unstable in running round a curve at a high speed, allows of its passing through a doorway of ordinary width, The third and last kind of single driver has the driving-wheel placed centrally in the rear of two steering-wheels. are mounted parallel and opposite to each other. The defect
of this arrangement is that the weight of the rider is too equally distributed over the three wheels, instead of coining more upon the driver than upon the other two.
There are several t vpes of doulde-driving tricycles, where the two driving-wheels are placed parallel and opposite to each other, with the steering,-wheel in front or behind, and generally central. though in smile cases it is placed in line with one of the driving-wheels, so that the innehine then only makes two tracks.
The two principal methods of double-driving are : first, by clutch-action ; and, secondly, by differential or balanee-gear.
In the clutch-m..00n plan the two driving,-wheels„ or the ehain-wheels driving them, are locked to their axle while the tricycle is being driven straight forward. but in running round a curve the outer wheel overruns the clutch, and the inner wheel alone drives, Of the various clutches so far devised, probably the hest results have been attained by that known as the Itourdon eluteh. It consists of a disk fixed upon the crank-axle, and having its circumference cut away so as to form a series inclined pla.nes, A box formingt he the chain-wheel encircles this disk, and in the recesses of the inclined planes which join between the disk and the box, and so lock them together as long as the axle is driving the wheel. Whenever the wheel has freed itself by overrunning the axle; there will always be at least one of the rollers ready (in every position) to instantaneously lock the two together again as soon as the speed of the wheel falls back to that of the axle. The pedals can remain stationary whenever the gradient of the road will allow the machine to run of itself, an advantage which economizes the ex penditure of power, as the feet of the rider can remain motionless for the time being. The brake, however, must be entirely relied on for checking the speed, as it can not be stopped by lioaek- pedaling. A clutch-driven machine can not be driven backward without some extra gearing. Many attempts have been made to construct a clutch that will drive automatically in both directions, bat the writer is not aware that any have proved successful, the reason of their failure being that they were not instantaneous in action.