Results of an experimental study of the flow of a viscous fluid down an inclined plane are presented. The contact line at the front of the flow is straight in the early stages of the flow, then becomes unstable to the formation of fingers. From measurements of the contact line position as a function of time for angles of inclination α in the range 0°<α≤32°, the flow is analyzed before and after the instability occurs, and the development of the finger pattern is parametrized.

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Reference 7 includes a calculation of the growth of small perturbations to the initially uniform front, which predicts exponential growth at small times. Most of our data lie well outside of this linear regime.
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