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Tag cpeed of locomotives has not increased with their weight and siz°. there :s a na^u^al law that stands in the way of this- If we double the weight on the driving-wheels, the adhesion, and consequent capacity for drawing loads, is also doubled. Eaa:oning in an analogous way it might be said that if we double the circumference of the wheels tbe distance that they will travel in ono resolution, and consequently the speed of the engine will be in a like proportion.

But. if this be done, it will require twice as much power to turn the large wheels as was needed for the small ones j and we then encounter tha the natural law that the rasistance increases as the square of the speed, and probably at even a greater ratio at very high velocities. At 90 miles an hour the resistance of a train is four times as great as it 18 at 30 milee. That is the pull on the draw-bar of t^ie engine must be four tim^s as great in the ono case as it i 8 ia tha other. But at 60 aiiies an hoar this pull must be exerted fur a givan distance in half the time it Js at 30 miles, so tbatlthe auaouutor power exerted and e'eana generated in a given perb.l of ttnae must be eight tim^s as great ia th 9 oue cjseasin theoth^r, Tuih nnans that the capacity of tha boiler, cylinders,

and the other parts must be greater, with a corresponding addition to the * eight of the machine. Obviously, if iha wtight per wheel is limited, we soon reach a point at which the size of the driving- wheels and other parts cannot be enlarged ; which means that there is a certain proportion of wheels, cylinders, and boiler which will give a maximum speed. — From American Locomotives and Cars, by M. N. Forney, in Scribnei's Magazine.

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Bibliographic details

THE LIMIT OF SPEED., Bruce Herald, Volume XX, Issue 2020, 7 December 1888

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THE LIMIT OF SPEED. Bruce Herald, Volume XX, Issue 2020, 7 December 1888

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