The story
It was experimentally derived independently by Jean Léonard Marie Poiseuille in 1838 and Gotthilf Heinrich Ludwig Hagen, and published by Poiseuille in 1840–41 and 1846.
Etymology from Wiktionary, CC BY-SA 4.0.
Hagen-Poiseuille equation
Today it means: A physical law that gives the pressure drop in an incompressible Newtonian fluid in laminar flow flowing through a long cylindrical pipe of constant cross section. Full definition →