"In other words, the track circuit is today the only medium recognized as fundamentally safe by experts in railway signaling whereby a train or any part thereof may retain continuous and direct control of a block signal while occupying any portion of the track guarded by the signal."
"To Mr. William Robinson the Patent Office records concede the honor of having devised the first practical track or 'Rail circuit'. This comprised what is termed the closed track circuit. * * * Closed track circuits are very reliable, wholly safe in principle, and simple of application and maintenance."
The above paragraphs, quoted from the third annual report of the Block Signal and Train Control Board to the Interstate Commerce Commission under date of November 22, 1910, ably express in a few words what the invention of the track circuit has meant to the railroads of this and other countries. In order, however, that those who are not familiar with the principles of the track circuit may have some general knowledge of them, a simple, non-technical description is given, as prepared some years ago by Mr. J. P. Coleman, of the Union Switch & Signal Company.
Historical information on the development and use of direct current and alternating current track circuits for roads using electricity for propulsion purposes and those using steam will be found in a report on this subject made by Committee X to the Railway Signal Association in 1910.
By J. P. Coleman.
Assuming that it is clearly understood that the current is generated at the battery; that it flows from thence through the conductors (of which the coils of the magnet form part) and back again to the battery, and that the magnet is simply a device interposed in the circuit for the purpose of transforming electrical energy into mechanical (magnetic) energy, and that the latter can exist in an electro-magnet only with the presence of the former, we are now prepared to make clear the principle of an electric track section.
To assist in this, let us state an invariable law governing the flow of currents: If two or more paths be presented an electric current, it immediately becomes divided, and flows in each in quantities directly in proportion to the conductivity of each.
The unit of electrical resistance, whereby the comparative merits of various materials and sizes of materials as conductors are designated, is called an ohm, (just as the unit of lineal measurement whereby the comparative lengths and sizes of various objects are designated, is termed a foot) and we will therefore use that term in reference to the resistance of a conductor.
