The block system is of English origin, and it scarcely needs to be said that it was adopted by the railroad corporations of that country only when they were driven to it by the exigencies of their traffic. But for that system, indeed, the most costly portion of the tracks of the English roads must of necessity have been duplicated years ago, as their traffic had fairly outgrown those appliances of safety which have even to this time been found sufficient in America. There were points, for instance, where two hundred and seventy regular trains of one line alone passed daily. On the London & North-Western there are more than sixty through down trains, taking no account of local trains, each day passing over the same line of tracks, among which are express trains which stop nowhere, way trains which stop everywhere, express-freight, way-freight, mineral trains and parcel trains. On the Midland road there are nearly twice as many similar trains on each track. On the Metropolitan railway the average interval is three and one-third minutes between trains. In one case points were mentioned where 270 regular trains of one line alone passed a given junction during each twenty-four hours,--where 470 trains passed a single station, the regular interval between them being but five-eighths of a mile,--where 132 trains entered and left a single station during three hours of each evening every day, being one train in eighty-two seconds. In 1870 there daily reached or left the six stations of the Boston roads some 385 trains; while no less than 650 trains a day were in the same year received and despatched from a single one of the London stations. On one single exceptional occasion 1,111 trains, carrying 145,000 persons, were reported as entering and leaving this station in the space of eighteen hours, being rather more than a train a minute. Indeed it may well be questioned whether the world anywhere else furnishes an illustration so apt and dramatic of the great mechanical achievements of recent times as that to be seen during the busy hours of any week-day from the signal and interlocking galleries which span the tracks as they enter the Charing Cross or Cannon street stations in London. Below and in front of the galleries the trains glide to and fro, coming suddenly into sight from beyond the bridges and as suddenly disappearing,--winding swiftly in and out, and at times four of them running side by side on as many tracks but in both directions,--the whole making up a swiftly shifting maze of complex movement under the influence of which a head unaccustomed to the sight grows actually giddy. Yet it is all done so quietly and smoothly, with such an absence of haste and nervousness on the part of the stolid operators in charge, that it is not easy to decide which most to wonder at, the almost inconceivable magnitude and despatch of the train-movement or the perfection of the appliances which make it possible.