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Where the road forms a curve of 2000 feet diameter, the difference between the length of the outer and the inner track is equal to 5 feet for every 1000 feet of road when the gauge is 4 feet, and nearly 6 feet to the 1000 for a 6 foot gauge. This difference causes the inner wheel to drag on the rail, thereby increasing the resistance and wearing out the tire. If, by this cause, one of the wheels gets worn out more than the other, its diameter will be smaller and the motion of the car in a straight line will become dangerous from the same cause: the larger wheel causes the smaller one to drag. If one of the wheels drags, the sliding friction produced thereby gives a tendency to the car to place itself crossways on the track. It is dangerous therefore to run at great speed even on a curve of 3000 feet diameter, and as this makes it necessary in building a railroad to avoid curves as much as possible, a road through a rugged or uneven country is very expensive. The axles have to be made unnecessarily strong as they have to sustain a twist from the same cause. An Austrian civil engineer undertook to avoid this difficulty by putting the wheels on a separate axle each and uniting the two halves oy different means; none of them, however, seems to us perfect enough to deserve recommendation, and we expect our inventors will come to the rescue and will find out some cheap and simple plan to give each of the wheels an independent motion from the other, still making the whole strong enough and safe against accidents.— Journal of the Society of Austrian Civil Engineers.
