TABLE OF TIME Occupied in running One Mile, Speed in Feet per Minute, and Number of Revolutions of the Driving Wheels, or Double Strokes of the Piston, per Minute, at the following given speeds. REVOLUTION OF WHEELS, PER MINUTE-THE DIAMETER OF WHEELS BEING IN FEET. 31⁄2 ft. 4 feet. 42 feet. 5 feet. 5% feet. 6 feet. 61⁄2 feet. 7 feet. 7% feet. 8 feet. | | 55 60 345-47 296. 259. 97.14 91. 94.5 98. | | 230-32 207.42 187.5 | 115.75 108.5 119.5 112. 132 123-23 | 115.5 136. 127-06 119. 149.38 137-62 128 138.16 129.5 | 143.90 133. | | | 242-77 218-63 197.95 182-05 168.03 156 145.63 136.5 | | | 284-30 | 252.27 229-23 | 210-06 193.95 180. 560-23 504-62 458-65 | 420-11 367.90 360 336. COMPARATIVE ELASTICITY OF WROUGHT AND CAST IRON. An able work on tubular bridges gives the following as the comparative elasticity of wrought and cast iron: "The mean ultimate resistance of wrought iron to a force of compression, as useful in practice, is twelve tons per square inch, while the crushing weight of cast iron is forty-nine tons per square inch, but for a considerable range, under equal weights, the cast iron is twice as elastic, or compresses twice as much as the wrought iron. "A remarkable illustration of the effect of intense strain on cast iron was witnessed by thè author, at the works of Messrs. Easton & Amos. The subject of the experiment was a cast-iron cylinder ten and five-eighths inches thick, fourteen and a half inches high, the external diameter being eighteen inches. If requisite for a specific purpose to reduce the internal diameter three and a half inches, this was effected by the insertion of a smaller cast-iron cylinder into the centre of the large one; and to insure some initial strain, the large cylinder was expanded by heating it, and the internal cylinder being first turned too large, was thus powerfully compressed. The inner cylinder was partly filled with pewter, and a steel piston being fitted to the bore, a pressure of 972 tons was put on the steel piston. The steel was 'upset' by the pressure, and the internal diameter of the small cylinder was increased by full three-sixteenths of an inch; i. e. the diameter became 311 of an inch! A new piston was accordingly adapted to these dimensions and in this state the cylinder continues to be used, and to resist the pressure; the external layer of the inner cylinder was thus permanently extended 3 of its length. In fact, it can only be regarded as loose packing, giving no additional strength to the cylinder. Under these high pressures, when confined mechanically, cast iron, as well as other metals, appears, like liquids, to exert an equal pressure in every direction in which its motion is opposed." 15 LOSS FROM RESISTANCES AGAINST THE PISTON, Produced by imperfect action of the Valves. This is a branch of the subject deserving especial consideration. Its importance, as referring to the economical working of steam-engines, may be profitably illustrated by a brief historical account of the consecutive alterations and improvements in the valve arrangements and mechanism of the locomotive engine, and of the results produced in the saving of fuel. It may be premised that the same principles have their application not only to the engines of other railways, making due allowances for difference in the gradients, and difference in the loads and dimensions of engines, and difference of speed, but also to fixed engines in general. The history of the locomotive engine may, for the sake of convenient classification, be divided into two periods-the first a period of increasing, the second a period of decreasing consumption, as respects the article of fuel. Brief allusion may be made to the events of both periods, and a reference to the causes which retarded as well as to those which accelerated improvement. During the first few years after the opening of railroads, the class of improvements comprising the gradual enlargement of dimensions, as necessary for maintaining higher rates of speed and the transport of heavy bodies, the better disposition and proportionment of the component parts, and the selection of suitable materials, capable of resisting heavy strains and various other causes of derangement and decay, demanded, in consequence of their direct influence upon the traffic of the companies, unremitting attention. The necessity of securing regularity in the transport of trains, whether of passengers or goods, was pressing and paramount, and afforded sufficient materials for thought and experiment. It is, therefore, a source of less surprise than regret, that little progress should have been |