Kosmos. Entwurf einer physischen Weltbeschreibung. 5 vols. and atlas.

This work includes founding material in geography, plant geography, orography, climatology and meterology, among other sciences, and citations to 9,000 sources. The atlas was issued without Humboldt's participation, and published by Krais & Hoffmann (1851). The fifth volume comprising the lengthy index, was issued after Humboldt's death. 

There were several English translations: by A. Prichard in 2 vols., London: H. Baillière, 1845; by Mrs. Eliz. Sabine, 4 vols, London: Longmans, 1846-58, and the most complete in 5 vols. by E. C. Otté (vols 1-3), Otté and B. H. Paul (vol. 4), and Otté and W. S. Dallas (vol. 5), London, 1849-52. The best introduction to the work is that to Vol. 1 by Nicolaas A. Rupke, Cosmos: A Sketch of the Physical Description of the Universe, Baltimore: Johns Hopkins University Press, 1997. There are numerous digital facsimiles available.