Exact closed solutions of the following equation of diffusionwhere m and n are considered to be independent, are obtained for the following cases: (1) diffusion from a line‐source embedded in a smooth surface; (2) diffusion from a smooth surface; (3) vapor concentration in the wake of an evaporating surface. The solutions for Cases (1) and (2) belong to the similarity‐solution category. Dimensional analysis has been used in the systematic search for such solutions in as concise a manner as possible. The solution for Case (3) can be obtained from those for Cases (1) and (2). Diffusion in Couette flow is given as an exam