Equations (22a) and (22b) in [1, p. 1045] should have been written as follows: \begin{align*} N_{/\!/}=&1-\frac {1}{\sqrt {1+(2R_{0}/h)^{2}}}\qquad \qquad \quad {(22a)}\\ N_{\bot }=&\frac {1-N_{/\!/}}{2}=\frac {1}{2\sqrt {1+(2R_{0}/h)^{2}}}. \quad{(22b)}\end{align*}