Granville T. Woods was a prolific African-American inventor and electrical engineer who held more than 60 patents, primarily for inventions related to trains and streetcars. One of his most significant inventions was the induction telegraph system, for which he received U.S. Patent No. 373,383,and 373,915 on November 29, 1887.
The Induction Telegraph System
Woods’s induction telegraph system was a groundbreaking invention that addressed a critical safety issue of the time: the inability of moving trains to communicate with each other or with stations. The system used the principle of electromagnetic induction to transmit messages without a direct wire connection.
Here’s how it worked:
- A coil or helix was placed on the train, connected to a telegraph or telephone in the operator’s cab.
- Another conductor, such as existing telegraph lines or a specially laid wire, was placed parallel to the tracks.
- As the train moved, the coil on the train would come into “inductive proximity” with the track-side conductor.
- When a signal was sent from a station or another train, it would create an electrical impulse on the track-side conductor.
- This impulse would then induce a corresponding current in the coil on the train, allowing the message to be received.
The system allowed for two-way communication, enabling train operators and dispatchers to send and receive messages in real time. This was a major safety improvement, as it allowed for the tracking of trains and the prevention of collisions.
Woods’s Legacy
Woods’s induction telegraph system was a significant commercial success. It was so effective that it faced a patent lawsuit from Thomas Edison, who claimed to have invented a similar device. Woods successfully defended his patent, earning him the nickname “Black Edison.” He also declined an offer from Edison to join his company, preferring to remain independent.
Woods’s work with the induction telegraph laid the foundation for his synchronous multiplex railway telegraph, which further improved communication by allowing multiple messages to be transmitted simultaneously. His innovations were purchased by major companies like General Electric, Westinghouse, and the American Bell Telephone Company, and his contributions to railway safety and technology continue to be used in modern transit systems today.
