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A. Upon well formed railways with carriages of good construction, the average tractive force required for low speeds is about 7-1/2 lbs. per ton, or 1/300th of the load, though in some experimental cases, where particular care was taken to obtain a favorable result, the tractive force has been reduced as low as 1/500th of the load.
The prince under whom the vast revenue thus stated is said to have been collected, ascended the throne on the death of his grandfather Abdullah, in the 300th year of the Hejra, and the 912th of the Christian era: and his reign, of more than fifty lunar years, saw the power and splendour of the Umeyyan dynasty attain its zenith.
If the total friction be 1/300th of the load, and the rolling friction be 1/1000th of the load, then the friction of attrition must be 1/429th of the load; and if the diameter of the wheels be 36 in., and the diameter of the axles be 3 in., which are common proportions, the friction of attrition must be increased in the proportion of 36 to 3, or 12 times, to represent the friction of the rubbing surface when moving with the velocity of the carriage, 12/429ths are about 1/35th of the load, which does not differ much from the proportion of 1/33d as previously determined.
A. I did not state that the resistance to traction was 1/500th of the weight upon an average to which condition the answer given to a previous question must be understood to apply but I stated that the average traction was about 1/300th of the load, which nearly agrees with my former statement.
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