[18] Many of the rates from Hull are affected by inland water competition, or by those charged from Liverpool. On the other hand, the rates from Hull govern those from Grimsby (as a competing port), Harwich, West Hartlepool, Newcastle, Sunderland and Shields. In fact, a large portion of the anomalies in railway rates arise from the competition between ports. Although improvements in detail as to such rates, no doubt, are possible, the interests of some ports would be seriously affected by any change in the principle on which railway rates are fixed. The chief explanation of differential rates have been mentioned; another cause less important is in operation. In carriage by road, cost may be roughly measured by distance, though even as to the expenses of cartage that is subject to exceptions. But this test--admitted to be practically useless as regards freight by sea--does not hold good of railway transport. Of the various kinds of outlay on the part of a railway company, a large portion remains fixed, whether the distance run by a train is ten miles or one hundred. Such, for example, are the cost of terminal accommodation, and the services of loading and unloading, and clerical work. Such, too, speaking broadly, are the interest on cost of construction, repairs of bridges and earthworks, the permanent staff of employés, and of signalling. Another kind of expenditure increases directly with the mileage run; for example, the provision of, and wear and tear of locomotives, rolling stock and permanent way, and liability for loss of or damage to goods in transit. Certain kinds of expenditure increase with the distance run, but not in the same ratio. Obviously wages, cost of locomotive power, and cost of haulage generally are not four times as much in the case of a train which has run a hundred miles as in one which has run twenty-five. With the progress of railways, with improved economy in the use of machinery, and in other ways, this tendency--recognised to some extent by the Legislature in the rates for short distance traffic--in expenditure not to increase in the same proportion as mileage distance, becomes an important element. The result of all this is to make mileage less a criterion of cost, and tends to place large towns at a greater distance at an advantage as compared with intermediate towns, and to give rise to differential rates.[19] It is also obvious that from many intermediate towns the quantities forwarded are not so large and regular as from terminal towns, and that from the former there is not a constant traffic to and fro. [19] See as to this Dr. Otto Michaelis’s _Differenzialtarife der Eisenbahnen_, in which the natural and necessary rise of differential rates in Germany is explained.