1. Humboldt included it in volume one of Kosmos and in his 1827 essay on geographical differences in climate, “Über die Haupt-Ursachen der Temperatur-Verschiedenheit auf dem Erdkörper”. See Kosmos 1: 176; CO 1: 336. The Edinburgh Encyclopedia, for instance, references Humboldt’s description of cloud formation and electrical storms in its section on Physical Geography. See Brewster 1832: 589.