"Invention of the Rail Circuit
"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 in distinction from the open form that preceded it." * * *
"Closed track circuits are very reliable, wholly safe in principle, and simple of application and maintenance."
* * * "Attention is therefore directed to the closed track circuit—the basis of all modern automatic signal systems that are entitled to recognition as embodying the highest attainments in the matter of safety."
"The Closed Track Circuit
"The closed track circuit in its simplest form consists of the two rails of a section acting as prime conductors, a generator maintaining a difference of potential between them when the rails are unoccupied, and one or more relays connected across the rails."
* * * "The closed track circuit maintains the relay, normally, in an energized state, and the influence of the train upon the rails is to totally de-energize it by shunting or short-circuiting the generator—a thing as effectively done by a single car or locomotive as by a train of any length, for all practical purposes."
* * * "A failure of the generator or a break in the circuit, whether in the rails themselves or in other parts of the circuit, produces the same effect upon the relay as that of a train upon the rails.
"This is in full conformity with the accepted principles of safe signaling, which give heed not alone to the action of the devices of the system under normal conditions, but embrace also an equal regard for safe results following derangements of them."
Historical Notes