Claim 2. "In combination with the electro-magnetic commutator having the described circuit connections, the rail sections A'A*, the one closing the circuit through the commutator, and thereby determining the battery to be connected to the other rail section, substantially as and for the purpose set forth."
It must be admitted that there does not seem to be a very long step between the disclosures of this patent and the present method of operating a distant signal by reversing current through a rail section.
It will be observed that in this patent one rail is used as a return for a plurality of batteries connected to independent opposite rail sections.
In an autograph letter addressed to the author by Professor Henry, secretary of the Smithsonian Institution, under date of October 14, 1875, the Professor discusses Robinson's peculiar method of using batteries in signaling by which he obtained the above wonderful durability of 180 days or more without renewal, and pronounced the results obtained "very remarkable." His discussion of the subject is somewhat suggestive of the principles of the storage battery.
Switches
In 1876, 7 and 8, Mr. Robinson made a number of installations on the Boston and Providence, Old Colony and the Boston, Lowell and Nashua railroads.
On the latter road, at Wilmington Junction, he equipped two parallel sections of the double track, including six switches, in this short space, five of them connected with one of the blocks. These sections were arranged as regular closed circuit blocks, operative under the moving trains. The switches were also connected up in such a way that every switch had to be closed and locked for the main line or the danger signal would be exposed against approaching trains. This installation was made in 1876.
The switch connection applied to these switches is shown in Fig. 5 and a general plan of the same is illustrated in Fig. 6. Both of these figures are reproductions from Robinson's aforesaid British patent of 1879.
Fig. 5.