Imagining a woman confessing her sins to a priest, Bloom
explores a bizarre fancy that their low whispers might be
overheard because of a hidden feature of the confession box:
"And I schschschschschsch. And did you chachachachacha? And
why did you? Look down at her ring to find an excuse.
Whispering gallery walls have ears. Husband learn to his
surprise. God's little joke." Whispering galleries are curved
structures which transmit sound waves unusually well, allowing
a person to hear the whispered words of another person at a
position far removed.
Some natural caves produce this effect, and some science
museums demonstrate it with pairs of concave parabolic dishes
that face one another across an empty space: standing at one
focus of the resulting long ellipse, a person whispers into
the nearby dish and the sounds are heard at the corresponding
focal point facing the distant dish. But Bloom has probably
heard of whispers carried in circular or hemispherical rooms,
most particularly the famous whispering gallery in the dome of
St. Paul's Cathedral in London. Gifford notes that "a low
whisper near one wall can be distinctly heard at the opposite
wall 108 feet away."
Starting in the 1870s, the distinguished British physicist John William Strutt, Baron Rayleigh, studied this remarkable effect in St. Paul's and discovered whispering-gallery waves: sound waves that propagate by clinging to the circular walls, rather than traveling across the intervening space. In the first two decades of the 20th century Lord Rayleigh developed sophisticated wave theories to account for the phenomenon. The sound waves, it appears, travel around the circumference of the gallery via air particles that move in elliptical trajectories.
All of this is doubtless far beyond Leopold Bloom's ken, but it seems possible, given his scientific curiosity, that he has heard of Lord Rayleigh's discoveries. The strange phenomenon of sound waves clinging to walls—illustrated here by a digital map of sound waves traveling around a cylinder of air equivalent in diameter to the cupola of St. Paul's—does uncannily echo Bloom's fanciful conceit that "Whispering gallery walls have ears."