A hydrophone record taken in a babbling brook
shows a series of these exponentially decaying
sinusoids, which
corresponds to the entrainments of about 9 bubbles. The frequency of
oscillation gives the bubble size: just like bells of different sizes,
big bubbles give out low notes and small bubbles give out high notes. It
is therefore apparent that the penultimate bubble (marked
C)
was smaller than the first bubble (A),
and that bubbles B
and
D were the largest bubbles detected.
Click here for the homepage of the Centre for Ultrasonics and Underwater Acoustics