A natural phenomenon in the service of industry
Since the very beginning, humans and animals have used sound as an information medium and as a means of measurement. Bats can locate their position by means of ultrasound. Dolphins can detect shoals of fish and other objects underwater using ultrasonic frequencies of up to 120 kHz, and are even able to determine the heartbeat rate of other animals. Probably the oldest type of sonic measurement used by human beings is to count the seconds between seeing a bolt of lightning and hearing the thunder in order to determine just how near a storm really is.