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Updated: June 1, 2025
The tractive force of paddle wheel steamers is ascertained by a dynamometer fixed on shore, to which the floating vessel is attached by a rope. Sometimes the power of an engine is ascertained by a friction break dynamometer applied to the shaft. Q. What will determine the amount of thrust shown by the dynamometer?
The duty of a locomotive engine is expressed by the weight of coke it consumes in transporting a ton through the distance of one mile upon a railway; but this is a very imperfect method of representing the duty, as the tractive efficacy of a pound of coke becomes less as the speed of the locomotive becomes greater; and the law of variation is not accurately known.
The substitution of mechanical for horse or hand power, for mixed machinery, e.g., threshing machines, chaff cutters, pumps, etc., has taken place largely, although it has made comparatively little progress for tractive purposes. It may indeed, be questioned if steam is so largely employed in the cultivation of land as it was twenty years ago.
The author is bound to say that they were, no doubt, influenced by the favorable circumstances of weather, and something is to be allowed also for the great length of train drawn, very long trains having a less tractive resistance per tun on a level than short ones, and something, possibly more than is commonly supposed, may have been due to the use of oil-tight axle boxes, the saponaceous compound known as 'railway grease' being nowhere in use on railways in the States.
In the course of their conversation, the latter strongly recommended a railway in preference to a tramroad. They also discussed the kind of tractive power to be employed: Mr.
A. There is the counter for telling the number of strokes the engine makes, and the dynamometer for ascertaining the tractive power of steam vessels or locomotives; then there are the gauge cocks, and glass tubes, or floats, for telling the height of water in the boiler; and in pumping engines there is the cataract for regulating the speed of the engine.
The boiler is 11 ft. long by 4 ft. 2 in. diameter; the grate area is 16.25 square feet; and the heating surface is, tubes, 1,216.5 square feet; fire-box, 97.0 square feet; total, 1,313.5 square feet. The boiler pressure is 140 lb., and the tractive power per lb. of steam pressure in the cylinders, 88 lb.
Its springs are rather to be sought in a physical disadvantage that is, in the mechanical inferiority of their frames, their relative lack of tractive capacity, their deficiency as brute engines.
But if even 7 lbs. per tun of the total weight be taken as the resistance at these speeds, the tractive force will be 11,004 lbs., which is more than one fourth the adhesion weight of 40,050 lbs.
Of clustered bodies in empty space, each will move along a line which is the resultant of the tractive forces exercised by all the rest, modified from moment to moment by the acquired motion; and the aggregation of such clustered bodies, if it eventually results at all, can result only from collision, dissipation, and the formation of a resisting medium.
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