1. H. Lamb, Lehrbuch der Hydrodynamik, Teubner, Leipzig, 1931, Appendix IV.
2. R. von Mises and K. O. Friedrichs, Fluid dynamics, Brown University Summer Session for Advanced Instruction and Research in Mechanics, 1941, pp. 140-143.
3. H. and B. S. Jeffreys, Mathematical physics, Cambridge University Press, Cambridge, 1946, Chapter 4.