Hagen-Poiseuille equation

Etymology
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.

Proper noun

 * 1)  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.