1. Terrestrial Radio Waves, Elsevier Publishing Company, New York-Houston, 1949, Chapters II-VI.
2. �ber gew�hnliche Differentialgleichungen mit Singularit�ten und die zugeh�rigen Entwicklungen willk�rlicher Funktionen
3. Eigenfunction Expansions, Oxford Univ. Press, 1946, Chapter II.
4. Electromagnetische Schwingungen, In Frank, P., and von Mises, R., Die Differential und Integralgleichungen der Mechanik und Physik, Volume II, Rosenberg, New York, 1943, p. 891.
5. and , The mode theory of tropospheric refraction and its relation to wave-guides and diffration. Meteorological Factors in Radio Wave Propagation. Report of a conference held on April 8, 1946, by the Physical Society and The Royal Meteorological Society. The Physical Society, London, 1946, p. 80.