Editing Alexander von Humboldt (section)

===The United States, 1804===
[[File:Louisiana1804a.jpg|thumb|1804 map of the Louisiana Territory. Jefferson and his cabinet sought information from Humboldt when he visited Washington, D.C., about Spain's territory in Mexico, now bordering the U.S.]]

Leaving from Cuba, Humboldt decided to take an unplanned short visit to the United States. Knowing that the current U.S. president, [[Thomas Jefferson]], was himself a scientist, Humboldt wrote to him saying that he would be in the United States. Jefferson warmly replied, inviting him to visit the [[White House]] in the nation's new capital. In his letter Humboldt had gained Jefferson's interest by mentioning that he had discovered [[mammoth]] teeth near the Equator. Jefferson had previously written that he believed mammoths had never lived so far south. Humboldt had also hinted at his knowledge of New Spain.<ref name="Schwarz-2001">{{cite journal |last=Schwarz |first=Ingo |date=2001-01-01 |title=Alexander von Humboldt's Visit to Washington and Philadelphia, His Friendship with Jefferson, and His Fascination with the United States |journal=Northeastern Naturalist |volume=8 |pages=43–56|doi=10.1656/1092-6194(2001)8[43:AVHVTW]2.0.CO;2 }}</ref>

Arriving in [[Philadelphia]], which was a center of learning in the U.S., Humboldt met with some of the major scientific figures of the era, including chemist and anatomist [[Caspar Wistar (physician)|Caspar Wistar]], who pushed for compulsory smallpox vaccination, and botanist [[Benjamin Smith Barton]], as well as physician [[Benjamin Rush]], a signer of the [[United States Declaration of Independence|Declaration of Independence]], who wished to hear about [[cinchona]] bark from a South American tree, which cured fevers.{{sfn|de Terra|1955|pp=175–176}} Humboldt's treatise on cinchona was published in English in 1821.<ref>{{cite book |first=Alexander von |last=Humboldt |url=https://www.biodiversitylibrary.org/item/14437 |title=An illustration of the genus Cinchona | publisher=Printed for J. Searle | location=London | year=1821 | doi=10.5962/bhl.title.715}}</ref>

After arriving in Washington D.C, Humboldt held numerous intense discussions with Jefferson on both scientific matters and also his year-long stay in New Spain. Jefferson had only recently concluded the [[Louisiana Purchase]], which now placed New Spain on the southwest border of the United States. The Spanish minister in Washington, D.C. had declined to furnish the U.S. government with information about Spanish territories, and access to the territories was strictly controlled. Humboldt was able to supply Jefferson with the latest information on the population, trade agriculture and military of New Spain. This information would later be the basis for his ''Essay on the Political Kingdom of New Spain'' (1810).

Jefferson was unsure of where the border of the newly-purchased [[Louisiana]] was precisely, and Humboldt wrote him a two-page report on the matter. Jefferson would later refer to Humboldt as "the most scientific man of the age". [[Albert Gallatin]], Secretary of the Treasury, said of Humboldt "I was delighted and swallowed more information of various kinds in less than two hours than I had for two years past in all I had read or heard." Gallatin, in turn, supplied Humboldt with information he sought on the United States.<ref name="Schwarz-2001"/>

After six weeks, Humboldt set sail for Europe from the mouth of the [[Delaware River|Delaware]] and landed at [[Bordeaux]] on 3 August 1804.