五十年、一百年与一百五十年

“A sand dune would not seem to be a very likely candidate as a natural sound generator. But dunes in many parts of the world squeak, roar or boom. Acoustic sands have been described in desert legend but have received little scientific attention. Recently scientists have conducted the first quantitative analysis of the properties of an acoustic dune called Sand Mountain near Fallon, Nev. After trying sev- eral different methods, they found that the sand boomed loudest when a trench was rapidly dug in it with a flat- bladed shovel. The sound was like a short, low note on a cello; it lasted for less than two seconds and was readily audible at a distance of 30 meters. …