 Humboldt himself did not keep track of all the various editions.He wrote specialized works on particular topics of botany, zoology, astronomy, mineralogy, among others, but he also wrote general works that attracted a wide readership, especially his "Personal Narrative of Travels to the Equinoctial Regions of the New Continent during the years 1799–1804" His "Political Essay on the Kingdom of New Spain" was widely read in Mexico itself, the United States, as well as in Europe.Many of the original works have been digitally scanned by the Biodiversity Library.