Lamek Hulthén and K. V. Laurikainen
Rev. Mod. Phys. 23, 1 (1951) - Published 1 January, 1951
Arnold M. Feingold
Rev. Mod. Phys. 23, 10 (1951) - Published 1 January, 1951
L. Infeld and T. E. Hull
Rev. Mod. Phys. 23, 21 (1951) - Published 1 January, 1951