We show that the k-th
eigenvalue of the Dirichlet Laplacian is strictly less than the k-th eigenvalue of the
classical Stokes operator (equivalently, of the clamped buckling plate problem) for a
bounded domain in the plane having a locally Lipschitz boundary. For a C2
boundary, we show that eigenvalues of the Stokes operator with Navier slip (friction)
boundary conditions interpolate continuously between eigenvalues of the Dirichlet
Laplacian and of the classical Stokes operator.