U.S. electrical engineer and inventor whose discoveries in the field of alternating-current (alternating current) phenomena led to the development of successful alternating-current motors. He was also a founder of the U.S. electrical industry.

Thomson left England for Philadelphia as a child and later taught chemistry and mechanics at the Central High School there. With a fellow teacher, Edwin J. Houston, he designed an arc lighting system that attracted financial backing and led to the founding (1880) of the American Electric Company in New Britain, Conn., of which Thomson held 30 percent of the stock and was chief electrical engineer. In 1882 a group from Lynn, Mass., bought controlling interest in the company and moved it to Lynn. Thomson went to Lynn with the company, which in 1883 was renamed the Thomson–Houston Electric Company, and remained there as a consultant to the General Electric Company, which was formed in 1892 by the merger of Thomson–Houston with the Edison General Electric Company.

In addition to his alternating-current motor, Thomson invented the high-frequency generator (1890), the high-frequency transformer, the three-coil generator, electric welding by the incandescent method, and the watt-hour meter. Thomson also did important work in radiology, improving X-ray tubes and pioneering in making stereoscopic X-ray pictures. He was the first to suggest the provision of a mixture of helium and oxygen for workers in caissons and tunnel borings to prevent caisson disease (bends). He held some 700 patents and received many awards.