1. The scholarly literature on Zöllner is limited. For a biography with selections of his correspondence, see Felix Koerber, Karl Friedrich Zöllner: Ein deutsches Gelehrtenleben (Berlin: Hermann Paetel, 1899). A more modern biography is Dieter B. Herrmann, Karl Friedrich Zöllner (Leipzig: B.G. Teubner, 1982), published on the occasion of the centenary of Zöllner’s death. See also idem, “Zöllner, Johann Karl Friedrich,” in Charles Coulston Gillispie, ed., Dictionary of Scientific Biography 14 (1976), pp. 627–630. For the local and cultural context, see Christoph Meinel, Karl Friedrich Zöllner und die Wissenschaftskultur der Gründerzeit (Berlin: Sigma, 1991).
2. Examples of the latter are Max Jammer, Concepts of Space: The History of Theories of Space in Physics (Cambridge, Mass.: Harvard University Press, 1954), pp. 179–180; republished (New York: Dover Publications, 1993), pp. 181–182, and C.J. Scriba and P. Schreiber, 5000 Jahre Geometrie: Geschichte, Kulturen, Menschen (Berlin, Heidelberg, New York: Springer, 2005), p. 427.
3. The significance of Zöllner’s discussion was first pointed out by Stanley L. Jaki, The Paradox of Olbers’ Paradox: A Case History of Scientific Thought (New York: Herder and Herder, 1969), pp. 158–164; see also Helge Kragh, “Geometry and Astronomy: Pre-Einstein Speculations of Non-Euclidean Space,” ArXiv:1205.4909v2 [physics.hist-ph] (2012), esp. pp. 20–34.
4. J.C.F. Zöllner, Grundzüge einer allgemeinen Photometrie des Himmels (Berlin: Mitscher & Röstell, 1861). On Zöllner’s instrument and its use in astronomy, see A. Pannekoek, A History of Astronomy (London: Allen & Unwin and New York: Interscience Publishers, 1961), pp. 385–387; D.B. Herrmann and D. Hoffmann, “Astrofotometrie und Lichttechnik in der 2. Hälfte des 19. Jahrhunderts,” NTM: Schriftenreihe für Geschichte der Naturwissenschaften, Technik und Medizin 13 (1976), 94–104, esp. 96–98; Klaus Staubermann, “The Trouble with the Instrument: Zöllner’s Photometer,” Journal for the History of Astronomy 31 (2000), 323–338; C. Serken and K.B. Staubermann, ed., Karl Friedrich Zöllner and the historical dimension of astronomical photometry: A collection of papers on the History of Photometry (Brussels: VUB University Press, 2000), which includes on pp. 162–178 a bibliography of Zöllner’s publications.
5. F. Zöllner, “Ueber eine neue Art von Pseudoskopie und ihre Beziehungen zu den von Plateau und Oppel beschrieben Bewegungsphänomenen,” Annalen der Physik und Chemie 110 (1860), 500–523 + Taf. VIII, No. 4.