There are two errors in the introductory sections of Moffatt (Reference Moffatt1964). Neither has any bearing on any other part of that paper, but it may be useful here to set the record straight.

The general solution of the Stokes equation $\boldsymbol{\nabla} ^{4}\psi =0$ of the form $\psi =r^{\lambda }f_{\lambda }(\theta )$ was stated in eqn. (1.2) of the paper, and degenerate forms for $\lambda =0,1,2$ in eqns. (1.3)–(1.5). Equation (1.3) for $f_{0}(\theta )$ is obviously incorrect. The correct expression [like (1.5) for $f_{2}(\theta )$ ] is

(0.1) \begin{align} f_{0}(\theta )=A+B\theta +C\cos 2\theta +D\sin 2\theta , \end{align}

for arbitrary constants $A,B,C,D$ .

The second error relates to the example sketched in figure 2(b) of Moffatt (Reference Moffatt1964). In this example, fluid is contained between a rigid lower boundary $\theta =0$ and an upper horizontal free surface $\theta =\alpha$ on which a uniform tangential stress is imposed. The stream function has the local similarity form $\psi \sim r^{2}f_{2}(\theta )$ . The boundary condition $v =0$ on $\theta =\alpha$ was incorrectly stated as $f'_{2} (\alpha )=0$ ; it should have been $f_{2} (\alpha )=0$ . With this change, the correct solution for the function $f_{2}(\theta )$ becomes

(0.2) \begin{equation} f_{2}(\theta )= \frac {2[\alpha -\theta +\theta \cos 2\alpha -\alpha \cos 2\theta ]+\sin 2\theta -\sin 2\alpha +\sin 2(\alpha -\theta )} {8[2\alpha \cos 2\alpha -\sin 2\alpha ] } \,. \end{equation}

Interestingly, the problem encountered by Moffatt & Duffy (Reference Moffatt and Duffy1980) for the ‘hinged-plate problem’ occurs here also at the same critical angle $\alpha =\alpha _{c}\approx 0.715 \pi$ , the similarity solution $\psi \sim r^{2}f_{2}(\theta )$ being dominant only for $\alpha \lt \alpha _c$ .