In spite of any theoretical or fanciful objections which may be urged against it, this appliance will be found an indispensable adjunct to any really heavy junction or terminal train movement. For the elevated railroads of New York, for instance, its early adoption proved a necessity. As for questions of temperature, climate, etc., as affecting the long connecting rods and wires which are an essential part of the system, objections based upon them are purely imaginary. Difficulties from this source were long since met and overcome by very simple compensating arrangements, and in practice occasion no inconvenience. That rods may break, and that wires are at all times liable to get out of gear, every one knows; and yet this fact is urged as a novel objection to each new mechanical improvement. That a broken or disordered apparatus will always occasion a serious disturbance to any heavy train movement, may also be admitted. The fact none the less remains that in practice, and daily subjected through long periods of time to incomparably the heaviest train movement known to railroad experience, the rods of the interlocking apparatus do not break, nor do its wires get out of gear; while by means of it, and of it alone, this train movement goes unceasingly on never knowing any serious disturbance.[20] [20] "As an instance of the possibility of preventing the mistakes so often made by signal men with conflicting signals or with facing points I have shown the traffic for a single day, and at certain hours of that day, at the Cannon Street station of the South Eastern Railway, already referred to as one of the _no-accident_ lines of the year. The traffic of that station, with trains continually crossing one another, by daylight and in darkness, in fog or in sunshine, amounts to more than 130 trains in three hours in the morning, and a similar number in the evening; and, altogether, to 652 trains, conveying more than 35,000 passengers in the day as a winter, or 40,000 passengers a day as a summer average. It is probably not too much to say, that without the signal and point arrangements which have there been supplied, and the system of interlocking which has there been so carefully carried out, the signalmen could not carry on their duties _for one hour without accident_." _Captain Tyler's report on accidents for 1870, p. 35._