The introduction of the bell-cord running through the train and enabling conductors to communicate promptly by means of it with the engineer, and signal him in case of danger, constitutes another source of safety, but is still a wonder to Europeans, who cannot understand why passengers do not tamper with it, and how they can resist the temptation to give false signals by means of it. The only answer is that our people are educated up to it, and being accustomed to govern themselves, they do not require any restraint to make them respect so useful a device. Aside from the inconveniences which used to arise occasionally from a rustic mistaking the bell-cord for a clothes-rack, and hanging his overcoat over it, or from an old gentleman grabbing hold of it to help him climb into an upper berth in a sleeping-car, it has been singularly exempt from efforts to pervert it to unintended uses. The application of the magnetic telegraph to railways wrought the first great revolution in despatching trains, and introduced an element of promptness and safety in their operation of which the most sanguine of railroad advocates had never dreamed. The application of electricity was gradually availed of in many ingenious signal devices for both day and night service, to direct the locomotive engineer in running his train, and interpose precautions against accidents. Fusees have also been called into requisition, which burn with a bright flame a given length of time; and when a train is behind time and followed by another, by igniting one of these lights, and leaving it on the track, the train following can tell by noting the time of burning about how near it is the preceding train. Torpedoes left upon the track, which explode when passed over by the wheels of a following train and warn it of its proximity to a train ahead, are also used. In the early days more accidents arose from switches than from any other cause; but improvement in their construction has progressed until it would seem that the dangers have been effectually overcome. The split-rail switch prevents a train from being thrown off the track in case the switch is left open, and the result is that in such an event the train is only turned on another track. The Wharton switch, which leaves the main line unbroken, marks another step in the march of improvement. Among other devices is a complete interlocking-switch system, by means of which one man standing in a switch-tower, overlooking a large yard with numerous tracks, over which trains arrive and depart every few minutes, can, by moving a system of levers, open any required track and by the same motion block all the others, and prevent the possibility of collisions or other accidents resulting from trains entering upon the wrong track.[25]