Some three thousand years ago according to the Old Testament, Joshua, the son of Nun, led the Israelites over the river Jordan into the promised land. And then, once each day for six days, seven priests carrying seven trumpets made of rams' horns circled the walled city of Jericho. And on the seventh day the priests circled the walls seven times, and on the seventh time the priests blew a loud blast on the trumpets, and the Israelites shouted a loud shout, and the walls of Jericho fell down flat. Thus must history reach back into antiquity to find the first allusion to the use of sound energy for a purpose other than hearing.

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