Louis (1804) Breguet

French physicist and watchmaker, noted for his work in the early days of telegraphy, and one of the 72 French scientists whose names are written around the base of the Eiffel Tower.

Educated in Switzerland, Breguet was the grandson of Abraham-Louis Breguet, founder of the watch manufacturing company Breguet. He became manager of Breguet et Fils watchmakers in 1833 after his father Louis Antoine Breguet retired.

Between 1835 and 1840 he standardized the company product line of watches, then making 350 watches per year, and diversified into scientific instruments, electrical devices, recording instruments, an electric thermometer, telegraph instruments and electrically synchronized clocks. With Alphonse Foy, in 1842 he developed an electrical needle telegraph to replace the optical telegraph system then in use. A later step-by-step telegraph system (1847) was applied to French railways and exported to Japan. He observed in 1847 that small wires could be used to protect telegraph installations from lightning, the ancestor of the fuse.

He also manufactured the rotating mirror Fizeau–Foucault apparatus, used by Léon Foucault and Hippolyte Fizeau to measure the speed of light (1850). In 1856 he designed a public network of synchronized electric clocks for the center of Lyon. In 1866 he patented an electric clock controlled by a 100 Hz tuning fork.

In 1870 he transferred the leadership of the company to Edward Brown. Breguet then focused entirely on the telegraph and the nascent field of telecommunications. He collaborated in the development of an induction coil, later improved by Heinrich Ruhmkorff.

Breguet was married and had one son Antoine (1851–1882) who also joined the family electrical business. With his son, he met Alexander Graham Bell and obtained a license to manufacture Bell telephones for the French market. He was the grandfather of Louis Charles Breguet, aviation pioneer and aircraft manufacturer. He died on 27 October 1883 in Paris, aged 78.