1. H. Schardin, Forsch. Gebiete Ingenieurw. B 5, Forschungs-heft 367, July–Aug. 1934;
2. translation by F. A. Raven, David Taylor Model Basin, Navy Department, Washington, D.C., Translation 156.
3. J. P. C. Southall,Mirrors, Prisms and Lenses(The Macmillan Company, New York, 1949), Chapter 9.