Charles Thomas Main (February 16, 1856 – March 6, 1943)[1] was an American mechanical engineer and business executive, who worked for New England textile mills, and also in the then new field of hydroelectricity.

[3] Main's father was a machinist and engineer, and this may account in part for Charles' early displayed fondness for scientific subjects and general work in mathematics.

Following his graduation, he spent three years (1876–79) as assistant in the laboratories of the institute, perfecting himself in the practical work of his profession.

He worked a year in Providence, Rhode Island, and then entered a partnership with power engineer Francis Winthrop Dean.

Aside from his professional activities, he was always interested in the problems of municipal and local government, and held numerous public offices and appointments.

[1] He is the originator of numerous devices and inventions, notably of a receiver pressure register for compound engines, which he perfected in 1884.