 Coffin's management also led the company towards an aggressive policy of buy-outs and mergers with competitors.Both strategies reduced competition in the electrical lighting manufacturing industry.By 1890, the Thomson-Houston company was the dominant electrical manufacturing company in the U.S. Nikola Tesla received U.S. Patent 447920, ""Method of Operating Arc-Lamps"" (March 10, 1891), that describes a 10,000 cycles per second alternator to suppress the disagreeable sound of power-frequency harmonics produced by arc lamps operating on frequencies within the range of human hearing.