1. R. Einaudi, Sulle configurazioni di equilibrio instabile di una piastra sollecitata da sforzi tangentiali pulsante, Atti. Accad. Gioenia Catania, in two parts: I) mem. 20, 1-5 (1936)
2. II) mem. 5, 1-20 (1937). Part I) deals with the rectangular plate having simply supported edges, II) with the rectangular plate assuming other boundary conditions. The theory is applied only to cases in which the steady part of the applied load is less than the lowest Euler load and the harmonic component is small in amplitude.
3. S. Goldstein, Mathieu functions, Trans. Cambridge Phil. Soc., 23, 303–336 (1937).
4. G. Gorelik, Resonanzerscheinungen in linearen Systemen mit periodisch veränderlichen Parametern, (in Russian), Zeit. tech. Phys., Leningrad, in three parts: I) 4, 1783–1817 (1934); II) 5, 195–215 (1935); III) 5, 489–517 (1935). Treats the nonhomogeneous “Mathieu equation” with a viscous damping term added. Among other things it is proved that the solutions of the homogeneous Mathieu equation with a damping term all tend to zero with increase of the independent variable if the solutions without damping are stable. (These observations were taken from the Zentralblatt f. Mech., 3, 302 (1935); 4, 18 (1936).)
5. G. Hamel, Über lineare homogene Differentialgleichungen zweiter Ordnung mit periodischen Koeffizienten, Math. Ann., 73, 371 (1912).