\pwȧ-zœy\, Jean–Léonard–Marie (1797–1869),
French physiologist and physician. Poiseuille is best known for his research on the physiology of the circulation of blood through the arteries. He published his research in an 1828 dissertation in which he demonstrated that blood pressure rises and falls on expiration and inspiration. His interest in blood circulation led him to study the flow rates of other fluids. In 1840 he formulated the law regarding the flow rate for the laminar flow of fluids in circular tubes. In 1847 he published the results of further experiments using ether and mercury. Gotthilf Hagen, a German hydraulic engineer, discovered Poiseuille's law independently in 1839.