The book Musurgia Universalis is famous
and has been since it appeared in 1650.
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| Vol. 2 (Af-x.10): plate between pages 302 & 303 |
The illustration depicts a piazza-listening device.
The voices from the piazza are taken by the horn up through the mouth of the statue in the room on the piano nobile above, allowing both espionage and the appearance of a miraculous event. more
The modern eavesdropping equivalent is the ventilation plenum. Acoustical ducting is something most people don't consider when concerned about eavesdropping. We do.
