U.S. professor of civil and structural engineering whose outstanding contribution was a method of calculating tendencies to produce motion (moments) in the members of a continuous framework, such as the skeleton of a building.

Cross was appointed professor of structural engineering at the University of Illinois, Urbana, in 1930; seven years later he became full professor at Yale, retiring in 1951. Among other honours, he received the Institution of Structural Engineers' (British) gold medal.

By the use of Cross's technique, known as the moment distribution method, or simply the Hardy Cross method, calculation can be carried to any required degree of accuracy by successive approximations, thus avoiding the immense labour of solving simultaneous equations that contain as many variables as there are rigid joints in a frame. He also successfully applied his mathematical methods to the solution of pipe network problems that arise in municipal water supply design; these methods have been extended to other pipe systems, such as gas pipelines.