  Benjamin Peirce  (b. April 4, 1809, d. October 6, 1880) was a professor at Harvard with interests in celestial mechanics, applications of plane and spherical trigonometry to navigation, number theory and algebra. In mechanics, he helped to establish the (effects of the) orbit of Neptune (in relation to Uranus). In number theory, he proved that there is no odd perfect number with fewer than four distinct prime factors. In algebra, he published a comprehensive book on complex associative algebras. Peirce is also of interest to philosophers because of his remarks about the nature and necessity of mathematics. 