1. Adams, W. G. (1892),Comparison of Simultaneous Magnetic Disturbances at Several Observatories, Phil. Trans. London (A)183, 131.
2. Birkeland, K. (1911),Sur la lumiere zodiacale, Comptes Rendes Acad. Sci. Paris152, 345.
3. Birkeland, K. (1913),Sur la conservation à l'origine du magnetisme terrestre, Comptes Rendes Acad. Sci. Paris157.
4. Breit, G., andTuve, M. A. (1925),A Test of the Existence of the Conducting Layer, Nature116, 357.
5. Canton, (1759),An Attempt to Account for the Regular Diurnal Variation of the Horizontal Magnetic Needle, Phil. Trans. London398.