A note on Taylor's stability rule

Analyzing the stability of the interface between two fluids of different densities which is accelerating normal to its surface, Taylor concluded a rule that "this surface is stable or unstable according to whether the acceleration is directed from the heavier to the lighter fluid or vice versa." We show by following Taylor's analysis that in the range where the acceleration of the interface is in the direction of the gravitational acceleration and its magnitude is smaller, this rule reverses direction. The interface is stable or unstable according to whether the acceleration is from the lighter to the heavier fluid or vice versa.