J. Schutten, H.W. Baron, T. van der Hauw and P.J. van Deenen, Dynamic measurement of film-thickness in gas bearings, Appl. Sci. Res. A 7, 429-436 (1958)
A.J.H. Boerboom, Theory of the aberrations in the focusing properties of a magnetic field with one plane of symmetry, Appl. Sci. Res. B 7, 52-62 (1957)