Fluid flow in porous media from the viewpoint of classical hydrodynamics.

His most important work was in the studies of classical hydrodynamics, fluid mechanics, mathematical analysis, and compressible-flow theory.

His theoretical studies into the oceanic tides not only "solved practically all the remaining tidal problems which are soluble within the framework of classical hydrodynamics and analytical mathematics" but laid the basis of a tidal prediction service (developed with A. T. Doodson) of great international importance.