He was appointed a tutor in mathematics at Columbia University in 1888 and was successively promoted to instructor in 1891, adjunct professor in 1894, and full professor in 1897.
Siya ay hihirangin ng isang propesor sa matematika at sa Columbia University at 1888 ay sunud-sunod itaas na magtuturo sa 1891, Adjunct propesor sa 1894, at ganap na propesor sa 1897.