In 1855, physiologist Adolf Fick first reported his now well-known laws governing the transport of mass through diffusive means.  Ficks work was inspired by the earlier experiments of Thomas Graham, which fell short of proposing the fundamental laws for which Fick would become famous. Ficks law is analogous to the relationships discovered at the same epoch by other eminent scientists: Darcys law (hydraulic flow), Ohms law (charge transport), and Fourier's Law (heat transport).
Ficks experiments (modeled on Grahams) dealt with measuring the concentrations and fluxes of salt, diffusing between two reservoirs through tubes of water. It is notable that Ficks work primarily concerned diffusion in fluids, because at the time, diffusion in solids was not considered generally possible. Today, Ficks Laws form the core of our understanding of diffusion in solids, liquids, and gases (in the absence of bulk fluid motion in the latter two cases).  When a diffusion process does not follow Ficks laws (which happens in cases of diffusion through porous media and diffusion of swelling penetrants, among others), it is referred to as non-Fickian'.