Sound of Waters in the Night

— During the five days which we passed in the neighbourhood of the Orinoco cataracts, it was striking to hear the thunder of the rushing torrents sound three times louder by night than by day.

In all European waterfalls the same phenomenon is remarked.

What can be its cause in a wilderness where there is nothing to interrupt the repose of nature?

Perhaps the currents of heated ascending air by causing irregular density in the elastic medium, impede the propagation of sound during the day, by the disturbance they may occasion in the waves of the sound; whereas, during the nocturnal cooling of the earth’s surface, the upward currents cease.— Humboldt’s Aspects of Nature.