The inside of a signal-box reminds one of a pianoforte on a large scale, the lever-handles corresponding with the keys of the instrument; and, to an uninstructed person, to work the one would be as difficult as to play a tune on the other. The signal-box outside Cannon Street Station contains 67 lever-handles, by means of which the signalmen are enabled at the same moment to communicate with the drivers of all the engines on the line within an area of 800 yards. They direct by signs, which are quite as intelligible as words, the drivers of the trains starting from inside the station, as well as those of the trains arriving from outside. By pulling a lever-handle, a distant signal, perhaps out of sight, is set some hundred yards off, which the approaching driver—reading it quickly as he comes along—at once interprets, and stops or advances as the signal may direct. The precision and accuracy of the signal-machinery employed at important stations and junctions have of late years been much improved by an ingenious contrivance, by means of which the setting of the signal prepares the road for the coming train. When the signal is set at “Danger,” the points are at the same time worked, and the road is “locked” against it; and when at “Safety,” the road is open,—the signal and the points exactly corresponding. The Electric Telegraph has also been found a valuable auxiliary in ensuring the safe working of large railway traffics. Though the locomotive may run at 60 miles an hour, electricity, when at its fastest, travels at the rate of 288,000 miles a second, and is therefore always able to herald the coming train. The electric telegraph may, indeed, be regarded as the nervous system of the railway. By its means the whole line is kept throbbing with intelligence. The method of working the electric signals varies on different lines; but the usual practice is, to divide a line into so many lengths, each protected by its signal-stations,—the fundamental law of telegraph-working being, that two engines are not to be allowed to run on the same line between two signal-stations at the same time.