[19] In regard to the interlocking system as then in use in England, Captain Tyler in his report as head of the railway inspecting department of the Board of Trade, used the following language in his report on the accidents during 1870. "When the apparatus is properly constructed and efficiently maintained, the signalman cannot make a mistake in the working of his points and signals which shall lead to accident or collision, except only by first lowering his signal and switching his train forward, then putting up his signal again as it approaches, and altering the points as the driver comes up to, or while he is passing over them. Such a mistake was actually made in one of the cases above quoted. It is, of course, impossible to provide completely for cases of this description; but the locking apparatus, as now applied, is already of enormous value in preventing accidents; and it will have a still greater effect on the general safety of railway travelling as it becomes more extensively applied on the older lines. Without it, a signalman in constantly working points and signals is almost certain sooner or later to make a mistake, and to cause an accident of a more or less serious character; and it is inexcusable in any railway company to allow its mail or express trains to run at high speed through facing points which are not interlocked efficiently with the signals, by which alone the engine-drivers in approaching them can be guided. There is however, very much yet to be effected in different parts of the country in this respect. And it is worth while to record here, in illustration of the difficulties that are sometimes met with by the inspecting officers, that the Midland Railway Company formally protested in June, 1866, against being compelled to apply such apparatus before receiving sanction for the opening of new lines of railway. They stated that in complying with the requirements in this respect of the Board of Trade, they '_were acting in direct opposition to their own convictions, and they must, so far as lay in their power, decline the responsibility of the locking system_.'" To still further perfect the appliance a simple mechanism has since 1870 been attached to the rod actuating the switch-bolt, which prevents the signal-man from shifting the switch under a passing train in the manner suggested by Captain Tyler in the above extract. In fact it is no exaggeration to say that the interlocking system has now been so studied, and every possible contingency so thoroughly provided for, that in using it accidents can only occur through a wilful intention to bring them about.