He is a great physicist and has the inductance unit "Henry". He has made outstanding contributions to the electric power industry. He invented the relay (the embryonic form of telegraph) and discovered the electromagnetic induction phenomenon earlier than Faraday, but he did not apply for a patent in time.
1830 In August, Henry had observed electromagnetic induction in the experiment, which was one year earlier than Faraday's discovery of electromagnetic induction. But at that time, Henry was concentrating on making a bigger electromagnet, and did not announce the experimental results in time, so he lost the right to invent. Henry's electromagnet contributed to the invention of telegraph, and the inventors of practical telegraph, Morse and Wheatstone, both adopted the relay invented by Henry.
Henry replaced the electromagnet with a powerful electromagnet with insulated wires, and connected each circuit with a battery relay in series to transmit the text signal. One wire in the circuit can be replaced by a ground wire for two round-trip wires.
The telegraph was invented by Morse in 1837.
So Henry invented the relay between 183 1 and 1837.