Alexander von Humboldt
Venezuela, 1799–1800

Armed with authorization from the King of Spain, Humboldt and Bonpland made haste to sail, taking the ship Pizarro from A Coruña, on 5 June 1799. The ship stopped six days on the island of Tenerife, where Humboldt climbed the volcano Teide, and then sailed on to the New World, landing at Cumaná, Venezuela, on 16 July.

The ship's destination was not originally Cumaná, but an outbreak of typhoid on board meant that the captain changed course from Havana to land in northern South America. Humboldt had not mapped out a specific plan of exploration, so that the change did not upend a fixed itinerary. He later wrote that the diversion to Venezuela made possible his explorations along the Orinoco River to the border of Portuguese Brazil. With the diversion, the Pizarro encountered two large dugout canoes each carrying 18 Guayaqui Indians. The Pizarro ' s captain accepted the offer of one of them to serve as pilot. Humboldt hired this Indian, named Carlos del Pino, as a guide.

Venezuela from the 16th to the 18th centuries was a relative backwater compared to the seats of the Spanish viceroyalties based in New Spain (Mexico) and Peru, but during the Bourbon reforms, the northern portion of Spanish South America was reorganized administratively, with the 1777 establishment of a captaincy-general based at Caracas. A great deal of information on the new jurisdiction had already been compiled by François de Pons, but was not published until 1806.

Rather than describe the administrative center of Caracas, Humboldt started his researches with the valley of Aragua, where export crops of sugar, coffee, cacao, and cotton were cultivated. Cacao plantations were the most profitable, as world demand for chocolate rose. It is here that Humboldt is said to have developed his idea of human-induced climate change. Investigating evidence of a rapid fall in the water level of the valley's Lake Valencia, Humboldt credited the desiccation to the clearance of tree cover and to the inability of the exposed soils to retain water. With their clear cutting of trees, the agriculturalists were removing the woodland's "threefold" moderating influence upon temperature: cooling shade, evaporation and radiation.

Humboldt visited the mission at Caripe and explored the Guácharo cavern, where he found the oilbird, which he was to make known to science as Steatornis caripensis. He also described the Guanoco asphalt lake as "The spring of the good priest" (" Quelle des guten Priesters "). Returning to Cumaná, Humboldt observed, on the night of 11–12 November, a remarkable meteor shower (the Leonids). He proceeded with Bonpland to Caracas where he climbed the Avila mount with the young poet Andrés Bello, the former tutor of Simón Bolívar, who later became the leader of independence in northern South America. Humboldt met the Venezuelan Bolívar himself in 1804 in Paris and spent time with him in Rome. The documentary record does not support the supposition that Humboldt inspired Bolívar to participate in the struggle for independence, but it does indicate Bolívar's admiration for Humboldt's production of new knowledge on Spanish America.

In February 1800, Humboldt and Bonpland left the coast with the purpose of exploring the course of the Orinoco River and its tributaries. This trip, which lasted four months and covered 1,725 miles (2,776 km) of wild and largely uninhabited country, had an aim of establishing the existence of the Casiquiare canal (a communication between the water systems of the rivers Orinoco and Amazon). Although, unbeknownst to Humboldt, this existence had been established decades before, his expedition had the important results of determining the exact position of the bifurcation, and documenting the life of several native tribes such as the Maipures and their extinct rivals the Atures (several words of the latter tribe were transferred to Humboldt by one parrot). Around 19 March 1800, Humboldt and Bonpland discovered dangerous electric eels, whose shock could kill a man. To catch them, locals suggested they drive wild horses into the river, which brought the eels out from the river mud, and resulted in a violent confrontation of eels and horses, some of which died. Humboldt and Bonpland captured and dissected some eels, which retained their ability to shock; both received potentially dangerous electric shocks during their investigations. The encounter made Humboldt think more deeply about electricity and magnetism, typical of his ability to extrapolate from an observation to more general principles. Humboldt returned to the incident in several of his later writings, including his travelogue Personal Narrative (1814–29), Views of Nature (1807), and Aspects of Nature (1849).

Two months later, they explored the territory of the Maipures and that of the then-recently extinct Atures Indians. Humboldt laid to rest the persistent myth of Walter Raleigh 's Lake Parime by proposing that the seasonal flooding of the Rupununi savannah had been misidentified as a lake.
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