= Inverted falling film
An <inverted falling film> flows on the underside of an inclined solid surface. Taking the normal coordinate from the solid into the liquid reverses the normal component of <gravity> relative to an upper-surface film. In the <Benney equation>, the hydrostatic contribution to the <volume flux per unit width> therefore changes from $-2\varepsilon h^3h_x\cot\alpha/3$ to its negative. Normal <gravity> then amplifies disturbances of long <wavelengths>, while <surface tension> resists short <wavelengths>.
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