4 ideas
In 1800 Humboldt found that Lake Valencia in Venezuela had no outlet and that its level had been falling for decades, exposing former islands as hills. He traced the drop to colonists clearing the surrounding forests and diverting streams for indigo and sugar irrigation. He concluded that stripping trees from slopes dries up springs, reduces the water held in the soil, and turns steady streams into destructive seasonal torrents.
At Calabozo on the Venezuelan llanos in 1800, local men drove about thirty wild horses and mules into a pond to catch electric eels for Humboldt. The eels repeatedly shocked the horses, stunning several and drowning some, until the fish had exhausted their electrical charge and could be pulled out safely with small harpoons. Humboldt used the specimens for direct experiments on animal electricity and recorded the numbness and joint pain from the shocks he took himself.
Humboldt carried barometers, chronometers, thermometers and a cyanometer so that every place could be fixed by altitude, temperature, latitude and sky colour. He then read those numbers relationally, asking how climate, elevation, vegetation and human settlement shape one another rather than cataloguing species in isolation. Precise measurement is treated as the way to reveal connections across a landscape, and those connections are presented alongside the observer's aesthetic experience of it.
In the Cumaná slave market Humboldt watched buyers open the mouths of newly arrived Africans to inspect their teeth, as dealers do with horses. He argued that slavery is the greatest evil afflicting humanity and that no economic justification for it survives such firsthand observation. He extended this to the colonial order generally, holding that systems built on coerced labour corrupt both law and social relations.