An investigation has been made of the surface phenomena accompanying liquid film flow on vertical planes. The object of the investigation was to study the mechanics of liquid film flow with particular reference to:- a) the interfacial area of the wavy liquid film b) the film thickness As a result of the investigation the author proposes:- 1. Theoretical expressions for the interfacial area of the wavy liquid film for "two-dimensional waves"; 2. New equations for the velocity distribution within the wavy film; 3. New flow zones and limiting Reynolds numbers; 4. A correlation of the film thickness data for all regimes of flow. 5. A method of measurement of the maximum velocity of the falling film. 6. A method of measurement of the wave length of wave motion at its inception. A new technique has been developed for:- 1. Recording the profiles of ripples 2. Experimental determination of the increase in interfacial area due to wave motion on liquid films.