1. Gauss, C.F.: Intensitas vis magneticae terrestris ad mensuram absolutam revocata. Gauss, Werke, herausgeg. von der Kgl. Ges. Wiss., Göttingen, Vol. 5, pp. 79–118 (1877). Ostwalds Klassiker, Nr. 53, The original work was published in 1833. A German translation was published in Pogg. Ann. 28 (1833) In this paper Gauss proposed a system of units of length, mass and time and called these units absolute units.
2. Lamont, J.: Handbuch des Erdmagnetismus. VIII + 264 pp. Berlin: Veit & Co. 1849. — Contains a comprehensive theory of geomagnetic observations, especially measurements of H and D.
3. Angenheister, G.: Das Magnetfeld der Erde, Instrumente und Meßmethoden. Handbuch der Experimentalphysik, herausgeg. von W. Wien und F. Harms, Vol. 25, I, pp. 525–585. Leipzig: Akadem. Verlagsges. 1928.
4. Chapman, S., and J. Bartels: Geomagnetism. Oxford: Clarendon Press 1940. — Instrumental questions are treated in chap. II (pp. 29–95) with a great number of bibliographic references on pp. 945–952.
5. Terrestrial Magnetism and Electricity. Physics of the Earth, Vol. VIII, edit, by J. A. Fleming. New York and London: McGraw-Hill 1939. — Geomagnetic instruments in general are treated by J. A. Fleming, H. F. Johnston, and H. E. Mccomb in chap. II (pp. 59–109), and a description of instruments used in magnetic prospecting is given by C. A. Heiland in chap. Ill (pp. 118–131). Corresponding bibliographic references are found on pp. 701–706.