A whispering gallery is a circular or elliptical enclosure, typically beneath a dome of a vault, in which whispers from one side can clearly be heard in other parts of the gallery. The sound waves travel the circumference, clinging to the walls.
The Statuary Hall in the US Capitol building is a well known example and St. Paul's cathedral in London is another. I've actually been to both and been able to experience the phenomenon myself.
The pictures in this post aren't mine, though. They're borrowed from Wikimedia Commons because when I was at St. Paul's, no was photography allowed. Even now, there is no photography in the Whispering Gallery. Having already snuck a picture in the crypt of Sir Christopher Wren's monument, I wasn't going to risk another clandestine picture.
To visit St. Paul's today, you can buy a ticket to see the Cathedral floor and the crypt. That also includes being able to climb up to the three dome galleries—the Stone Gallery, the Golden Gallery, and the internal Whispering Gallery.
In regency London, tourists had a similar opportunity to explore the cathedral. Aside from when the church was open for services, its doors were locked. However, people could pay to enter to see "the curiosities". The Picture of London, for 1807 says:
At all other times the doors are shut and no persons admitted but such as are willing to pay for seeing the church and its curiosities. Strangers will find admittance by knocking at door of the northern portico. A person is within to pass the visitor to the stair case leading the curiosities for which he demands four pence.
It goes on to describe how much had to be paid to see the library, a model of Sir Christopher Wren's original design, the clockwork, and the Great Bell. It elaborates on the details of each curiosity and the cathedral including the Whispering Gallery, which would have cost twopence to see.
My Dear Friend is set in London and its characters discuss where to go and what amusements they enjoy. Darcy mentions the phenomenon of the Whispering Gallery, and at the end of the book, Elizabeth arranges a meeting there with her anonymous correspondent.
The Whispering Gallery is at the top of 259 steps, 99 feet above the nave. It's a circular walkway at the base of the dome. The effect of whispering works better than shouting—provided there isn't much background noise—because whispers are low intensity sounds, meaning there's less interference from distortions like echoes. The sound bounces off the curved wall of the walkway that sits at the base of the dome. You get a better result if you whisper along the wall rather than at the wall.
Darcy and Elizabeth wouldn't have understood how the sound traveled along concave surfaces in 1812. Lord Rayleigh explained it in the late 1870s. He was a Nobel winning mathematician and physicist. He explained how waves crept along the wall by reflection—and not by bouncing around the dome above. Whether or not you understand the how, it's pretty cool and a fun setting for a private and romantic encounter.
Have you been to any place that has a whispering gallery or St. Paul's? If you read My Dear Friend, what did you think of the scene set there?
The Picture of London, for 1807. John Feltham. Lewis and Hamblin, Paternoster-Row; For Richard Phillips, Bridge-Street, Blackfriars, 1807. London. https://books.google.com/books?id=j9MHAAAAQAAJ&newbks=1&newbks_redir=0&dq=picture%20of%20London%201807&pg=PR3#v=onepage&q&f=false
I loved that scene in the story! One of these years I would love to visit to see it for myself ~ Glory