Immediately on the completion of this open circuit installation Mr. Robinson began to look for weak points about it, and soon discovered several now well known as inherent in all normally open circuit systems, not the least of which was that if the circuit were broken or the current failed from any cause the signal would remain at safety, thus showing a false signal although danger might be imminent, a radical error in principle fatal to the reliability of any normally open circuit system of signaling. He therefore, after much study, devised the closed track circuit system, the construction and operation of which are clearly described above by the Interstate Commerce Commission. In devising this system Mr. Robinson reasoned that to make an efficient and reliable system every pair of wheels in the train must control the signal, whereby a single car on the block, or a break in any part of the circuit, or loss of current from any cause affecting the relay, would keep the signal at danger as effectively as the presence of a whole train on the block. These considerations led him to the invention of the closed track circuit operating as heretofore clearly described by the Interstate Commerce Commission. Before making tests of the system, however, he applied for and was allowed basic patents on the closed track circuit system in the United States and France, the United States patent dated August 20, 1872, No. 130,661, and the French patent February 29, 1872, No. 94,393. Having all the signal apparatus in operation at Kinzua, in the open circuit system, as above described, it was a simple matter for him to test the closed circuit system at this point. He therefore divided the opposite rails of the track into sections insulated from the adjacent continuous track rails and connected the relay terminals to these sections at one end and similarly connected a battery thereto at a suitable distance from the relay, thus forming a closed track circuit. This being done, the first train that passed connected the opposite rail lines through the wheels and axles, short circuited the relay, thus operating all the signal circuits under its control, thereby practically demonstrating the feasibility of the system. This was in 1872. This block was extended to the agent's station over a mile from the signal, at which station the track battery was placed and also a switch for the manual operation of the signal, and also an overlapping telltale signal showing to the agent when the distant main signal was actually exposed at danger. The signal also indicated to the agent the approach of a train when a mile away.