In the early 1920s, Iowa State pioneered a new measurement of horsepower by inventing a machine that could measure the pulling strength of a team of horses. Earlier horse dynamometers measured only the force required to move a load, not the force required to start pulling a load.
The device, “Iowa Dynamometer Car for Horses,” was patented by E. V. Collins and J. B. Davidson in 1926.
More agricultural engineering materials can be found in the Agricultural and Biosystems Engineering Digital Collection and at the Department of Agricultural and Biosystems Engineering space in the Digital Repository.
College of Agriculture and Life Sciences. “Department of Agricultural and Biosystems Engineering 125th Points of Pride,” August 1, 2017. https://www.cals.iastate.edu/content/department-agricultural-and-biosystems-engineering-125th-points-pride
Palmquist, John Gustaf, “A drawbar dynamometer for direct reading of horsepower” (1949). Retrospective Theses and Dissertations. 16325.