1. Electromagnetic Theory. McGraw-Hill, New York, 1941, Ch. 5.
2. Ordinary Differential Equations. Dover, New York, 1944, pp. 52–54.
3. Lectures on the Differential Geometry. The University Press, Cambridge, 1920, p. 419.
4. Das allgemeine beugungsproblem und die separation der maxwellschen gleichungen nach bromwich
5. Ioc. cit., p. 82.