Alexander von Humboldt

In a letter written on 5 June, the day they sailed, he said he would collect plants and fossils and make astronomical observations, but that the main aim of the journey was to observe how the forces of nature act together.

On 20 June they climbed up from Santa Cruz before sunrise; he found the town cool after the heat of the port, and noted that of its 9,000 inhabitants nearly 400 were monks.

They set out for the summit on 21 June and spent a cold night at the 'Station of the English', where two leaning rocks form a kind of cavern; the next day they examined the crater.

Because of typhoid on board, the ship changed course from Havana and they landed on 16 July. What he saw at the town's slave market made him a lasting advocate of abolition.

On 18 September they went to the cave with monks from the Caripe convent. The entrance arch was 80 feet wide and 72 high, and measuring with a cord they went about 430 feet in before lighting torches. Humboldt made the cave's nocturnal oilbird known to science.

They arrived on 21 November and stayed until early February. On 2 January, the night before climbing the Silla, he and Bonpland stayed up at a coffee plantation below it observing occultations of Jupiter's satellites.

Investigating the rapid fall in the lake's level, he put it down to the clearing of forests, which left the soil unable to hold water; it is here that he is said to have formed his idea of human-induced climate change.

On 19 March they watched local people drive wild horses into a pool to bring electric eels out of the mud; examining the eels they caught, both men received strong shocks.

They spent three nights lodging with the commander of the fort. Told here that political circumstances made it hard to pass into Portuguese territory (Brazil), they did not go down to the Amazon.

Having ascended the Casiquiare, they reached the bifurcation of the Orinoco on 20 May, confirming the link between the Orinoco and Amazon basins. At the mission opposite, the Indians were celebrating their return from gathering Brazil nuts and the liana that yields curare poison.

After their long life in the forests, he wrote of the pleasure of seeing wheaten bread on the governor's table. Soon both fell ill with fever, and Bonpland was in a dangerous state for several weeks, so they stayed a whole month in the town.

They arrived on 19 December after a passage of 25 days from Nueva Barcelona. His first task was to survey the city and the nearby towns of Guanabacoa and Regla.

On 14 March, on the way to Cartagena, they put in at the Río Guaurabo and rode up to the town; he spent much of the night observing stars and fixed the latitude near the cathedral.

They entered the port on 30 March. On the advice of the people he consulted here, he gave up the sea route by the Isthmus of Panama and decided to travel overland along the Andes by Bogotá, Popayán and Quito towards Peru.

The end of the voyage up the Magdalena. Humboldt wrote that of their twenty rowers they left eight behind on the way, and as many arrived with festering sores.

They arrived on 6 July and stayed until 8 September. The botanist José Celestino Mutis, head of the Royal Botanical Expedition to New Granada, gave Humboldt access to the huge pictorial record he had compiled since 1783.

They arrived on 6 January and stayed in the house of Juan Pío Montúfar, whose son Carlos de Montúfar joined the expedition from then on.

On 23 June he climbed with Bonpland and Montúfar until an impassable cleft forced them back; the height they reached, 19,286 feet, was a record at the time.

They arrived after the upper Amazon and the Inca remains around Cajamarca, having crossed an Andean range four times; this ended the second expedition.

On 9 November, at Lima's port, he observed the transit of Mercury to fix the longitude of Lima, and studied the fertilising properties of guano.

He visited on the way to Mexico City and, impressed by its climate, called it the City of Eternal Spring.

They arrived in April and spent about nine months there. Pointing to the Royal College of Mines, the Royal Botanical Garden and the Academy of San Carlos, he wrote that no city of the new continent, the United States included, had such solid scientific establishments.

On 8 August he visited the Valenciana silver mine, then the most important in the Spanish empire. He studied not only its geology but the whole mining complex and its output figures, which went into the mining section of his Political Essay on the Kingdom of New Spain.

On 19 September he climbed to the summit of the volcano, which had risen out of the ground 44 years earlier.

Arriving from Havana, he met the chemist and anatomist Caspar Wistar, the botanist Benjamin Smith Barton and the physician Benjamin Rush, a signer of the Declaration of Independence.

Led by Charles Willson Peale, the party arrived on 1 June, and Humboldt talked with President Jefferson about New Spain; Treasury Secretary Albert Gallatin said he learned more in less than two hours than in the previous two years.