Sound commentary

I’m tickled to see that the feature article “Medical Diagnostic Ultrasound” (Physics Today, March 2007, page 44 ) is by my neighbor, Carr Everbach, and I enjoyed it. He starts by mentioning “sounding” water depths from the sound given by a lead weight hitting the bottom; he also mentions “the propagation time” and that the phrase “to sound something out” is connected.

I’m puzzled, though, since the sound of the sounding lead hitting the soft, muddy Mediterranean Sea bottom would hardly be heard in the air, given the acoustic mismatch. Is there evidence that stethoscopes were held against the ship’s hull? Or did someone perhaps press an ear against the hull?

The online edition of the Oxford English Dictionary says that “sound” in this meaning is simply related to water, alas, and not to aural sound. Moreover, the speed of sound in water is so high that the tiny propagation-time interval for sound to travel from the sea bottom is hard to discern. Maybe that interval was the fall time in water, a viscous medium?

Perhaps Carr has other evidence, so I may sleep soundly about this.