Kac served at Cornell as an instructor from 1939 to 1943 (the year he became a US citizen), assistant professor from 1943 to 1947 when he was promoted to full professor.
Kac served sa Cornell bilang isang propesor mula sa 1939 sa 1943 (ang taon na siya ay naging isang mamamayan ng Estados Unidos), assistant professor 1943-1947 kapag siya ay itaas sa buong propesor.