* * * "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 In this connection a few historical notes on the origin and introduction of the closed rail circuit system of automatic electric block signaling on railroads may prove of interest. In 1870 Mr. William Robinson exhibited at the American Institute Fair held in New York City, an elaborate working model of an automatic electric signal system for railroads. This was a road crossing signal operated by trains approaching in either direction. When at a suitable distance the train set a gong ringing at the road crossing ahead, which continued sounding an alarm until the train had passed, when it ceased ringing. In this model the relays were de-energized by short circuiting, although the signal was operated on the normally open circuit plan. This is believed to be the first case in which short-circuiting had been used in the operation of railway signals. In 1871 Mr. Robinson installed this system as an automatic block signal on a block over a mile in length, at Kinzua, Pa., on the Philadelphia and Erie Railroad. This installation embodied a relay, a large visual signal under control of the relay, a heavy electric gong operated in conjunction with the visual signal, all at the signal station. From this station an overlap extended to the agent's station a mile ahead. Here a signal bell was provided so that when the visual signal was actually in the danger position it closed circuit on the bell magnet in the agent's station, the hammer remaining against the bell until the reversal of the distant signal opened the circuit of this check signal. This system worked perfectly, performing all claimed for it; but it was a normally open circuit system, the only principle ever dreamed of up to that time for operating an automatic electric railway signal.