See Catherine Goldstein & Jim Ritter (2003) "The varieties of unity: sounding unified theories 1920-1930" in A. Ashtekar, et al. (eds.), Revisiting the Foundations of Relativistic Physics, Dordrecht, Kluwer, p. 93-149; Vladimir Vizgin (1994), Unified Field Theories in the First Third of the 20th Century, Basel, Birkhäuser; Hubert Goenner On the History of Unified Field TheoriesArchived 2011-08-05 at the Wayback Machine.
See Catherine Goldstein & Jim Ritter (2003) "The varieties of unity: sounding unified theories 1920-1930" in A. Ashtekar, et al. (eds.), Revisiting the Foundations of Relativistic Physics, Dordrecht, Kluwer, p. 93-149; Vladimir Vizgin (1994), Unified Field Theories in the First Third of the 20th Century, Basel, Birkhäuser; Hubert Goenner On the History of Unified Field TheoriesArchived 2011-08-05 at the Wayback Machine.