Describes the flow rate through laminar flow resistors (capillary tube, gap). It is assumed, based on a steady-state laminar flow and a constant cross section flow, that the compressive force will be balanced out by the opposing force from the internal friction of the fluid resulting from its viscosity. The relationship between flow rate and pressure difference is a linear one. This law was discovered by Gotthelf Hagen in 1839 and shortly afterwards (independently) by George Gabriel Stokes.
Fluidlexikon