1. N. Bohr, Phil. Mag. 26(1), 476–857 (1913)
2. N. Bohr, D. Kgl. Danske Vidensk. Selsk. Skrifter, Naturvidensk. og Mathem. Afd. 8, IV, 1 ( 1918), reproduced in: J. Rud Nielsen (ed.) Niels Bohr Collected Works, Vol. 3 (North-Holland, Amsterdam, 1976) with an interesting introduction by the editor. Further reprinted by Dover (2005) under Bohr’s original On the Quantum Theory of Line-Spectra
3. U. Hoyer (ed.), Niels Bohr Collected Works, Vol. 2 ( North-Holland, Amsterdam, 1981)
4. M. Abraham, Theorie der Elektrizität ( Teubner, Leipzig, 1905)
5. H.A. Lorentz, The Theory of Electrons ( Teubner, Leipzig, 1909)