Engineers have brought railways to their present stage of perfection, and the public will expect them to devise and carry out still further improvements as the march of development moves onward. It is a simple 359 matter to arrange the traffic on a railway when all the works and appliances are appropriate for the service to be performed; but the advances which are made follow one another so rapidly as to necessitate constant study and organization to effect the structural alterations and additions requisite to maintain an up-to-date standard of efficiency. The traffic manager on a railway receives his instructions from the directors or controllers of the company as to the working out of the train service, rates, charges, and other items of his department, but the engineer has to stand alone, and his technical knowledge and professional skill must enable him not only to design and construct works suitable in character, extent, and strength to the duty for which they are intended, but also to decide when structures are no longer capable of properly sustaining the increasing loads brought upon them, and must be taken down and replaced with others of a stronger description. For this reason the engineer must carefully consider every circumstance and local feature which may influence the design to be prepared; he must thoroughly investigate the nature of the ground for foundations, as the description when ascertained will frequently determine the class of work to be erected, whether in viaducts, bridges, or buildings; and in his selection of materials and calculations for strength, he must allow ample margin to meet further increased weights, as well as for natural deterioration. He should, indeed, go a little further, and as his perceptive ability and training will always enable him the more readily to foreshadow the direction in which improvements or changes are tending, he should study out and be prepared with his schemes to meet the new departures as the requirements gradually arise. Strength and efficiency are the leading points which must be always kept in view, and the engineer must never forget that he is solely responsible for the safety of the line and works, and of the public passing over the same. INDEX 361 A Accommodation works, 12 Air-lock, 119 Air-pump, 120 Allowances for sinkage on embankments, 70 Alteration of gradients, 12 ---- of roads, 6, 10 American hand-brake, 46 Analysis of steel rails, 193 Approach roads to stations, 249 Arch culverts, 76 Automatical gate-alarm, 336 B