Humboldt in the Americas: 1799–1804

Humboldt and Bonpland left La Coruña on the ship Pizarro on 5 June 1799. They had meant to reach Havana, but an outbreak of typhoid on board made the captain change course, and they landed at Cumaná, Venezuela, on 16 July. Humboldt recalled anchoring about nine in the morning, forty-one days after leaving Corunna. The detour decided the whole journey: it opened the way to the Orinoco.

Location precision: The sources name the town of Cumaná, not a landing spot; the pin marks the city centre.

From the mission at Caripe, Humboldt explored the Guácharo cavern and found the oilbird, which he later made known to science as Steatornis caripensis. He wrote that the guácharo is about the size of a fowl and that the cave is at least 900 metres, or 2,800 feet, long. He had expected little new, but "the reality far exceeded my expectations." The cave remains a place to visit near Caripe.

Visitor guidance: The cave lies near Caripe in Monagas state; check opening times locally before you go.

In the plains near Calabozo, around 19 March 1800, the pair met electric eels whose shock could kill a man. They first wanted to experiment in the house where they lodged, but locals suggested they drive wild horses into the river to tire the eels. In less than five minutes two horses drowned; the eel, Humboldt noted, was five feet long. The fight pushed him to think about electricity and magnetism.

Location precision: Humboldt describes the pools around Calabozo, not one pond; the pin marks the town.

The four-month river trip covered 1,725 miles and aimed to establish the Casiquiare canal, the natural link between the Orinoco and Amazon systems. Unknown to Humboldt, its existence had been established decades earlier, but he fixed the exact position of the bifurcation. On the same journey he laid to rest the persistent myth of Walter Raleigh's Lake Parime.

Location precision: The trip ran along many rivers; the pin marks the Casiquiare, not a single camp.

After reaching Quito on 6 January 1802, Humboldt, Bonpland and the Ecuadorian nobleman Carlos Montúfar tried to climb Chimborazo in June 1802. They reached 19,286 feet (5,878 m), a record for a Westerner at the time, but about 1,000 feet short of the summit. Altitude sickness forced them to turn back.

Location precision: The sources give the altitude reached, not the spot; the pin marks the mountain's summit.

At Callao, the main port for Peru, Humboldt observed the transit of Mercury on 9 November. There he also studied the fertilizing properties of guano, rich in nitrogen. The cold current off this coast carries his name, though José de Acosta had found it 250 years before him. In Callao the Real Felipe Fortress still stands.

Location precision: The sources say Callao, not where he set up his instruments; the pin marks the Real Felipe Fortress.

Visitor guidance: The fortress is in Callao's Monumental Zone.

On 8 August 1803 Humboldt visited the Valenciana silver mine in Guanajuato, then the most important in the Spanish empire; the mine produced 60% of the world's silver in the 18th century. He studied the entire mining complex and analysed its output statistics. Local guides take visitors around the old facilities and down a long, steep staircase; the mine mouth is directly behind the wall of San Cayetano church.

Visitor guidance: Guided visits go underground; a modern museum stands on the site.

Leaving Cuba, Humboldt made an unplanned short visit to the United States. He had written to Thomas Jefferson, mentioning mammoth teeth he had found near the Equator, and Jefferson invited him to the White House. When Jefferson was unsure where the border of the newly bought Louisiana lay, Humboldt wrote him a two-page report. He sailed for Europe from the mouth of the Delaware and landed at Bordeaux on 3 August 1804.

Location precision: The sources place the talks in Washington and mention the invitation to the White House, but not the room.

Visitor guidance: The White House is at 1600 Pennsylvania Avenue NW.