 This was a world record at the time, but 1000 feet short of the summit.Humboldt's journey concluded with an expedition to the sources of the Amazon "en route" for Lima, Peru.At Callao, the main port for Peru, Humboldt observed the transit of Mercury on 9 November and studied the fertilizing properties of guano, rich in nitrogen, the subsequent introduction of which into Europe was due mainly to his writings.