 Upon his return to the United States, he worked at the New York State Agricultural Experiment Station (part of Cornell University) in Geneva, New York, and then at the University of Michigan before being hired in 1906 by Stephen M. Babcock of the University of Wisconsin to conduct what later came to be known as the "single-grain experiment", which ran from May 1907 to 1911.This experiment entailed a long-term feeding plan using a chemically balanced diet of carbohydrates, fat, and protein instead of single-plant rations as done in Babcock's earlier experiments of 1881 and 1901.Hart directed the experiment, Babcock provided ideas, and George C. Humphrey oversaw the welfare of the cattle during the experiment.