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The measurement of viscosity by optical techniques applied to a falling liquid film

Oil is placed on a flat vertical surface and flows down under gravity. Theory shows that the oil should take up a parabolic profile, the square of the thickness being directly proportional to the viscosity and inversely proportional to the time from the start of flow. This suggests a method of viscosity measurement which has a number of potential advantages. The paper gives interferometric measurements of oil films showing that, except near the upper edge of the film, the theory is accurately followed. Comparisons with a U-tube viscometer show discrepancies, probably arising from lack of temperature control and other inadequacies in the apparatus. An optical technique suitable for practical implementation of the method is suggested.