Humboldt an <persName xmlns="http://www.tei-c.org/ns/1.0" ref="https://edition-humboldt.de/H0000278 http://d-nb.info/gnd/119463288">David Friedländer</persName>, <placeName xmlns="http://www.tei-c.org/ns/1.0" ref="https://edition-humboldt.de/H0008564 https://www.geonames.org/3117735">Madrid</placeName>, 11. April 1799 (<bibl xmlns="http://www.tei-c.org/ns/1.0" corresp="https://edition-humboldt.de/WFDJIWK6">Humboldt 1973</bibl>, 657). Vgl. <bibl xmlns="http://www.tei-c.org/ns/1.0" corresp="https://edition-humboldt.de/6MZW66HE">Bersier 2017</bibl>.