Perspective machine by Filippo Brunelleschi, Florence, ca. 1400
From Drawing Academy:
“As the story goes, one sunny morning in Florence, Italy, Filippo Brunelleschi appeared at the gate of the not-yet-completed cathedral, holding a little painting and a little mirror. Already considered a magician by half of Florence because of the dome he was building without any scaffolding, Master Filippo gathered a sizable crowd for his demonstration.
Brunelleschi led the crowd to the gate of the cathedral so that they would look in the direction of the Baptistery outside the building. He gave a painting with a hole in the middle to somebody in the crowd and asked him to keep the unpainted backside of the painting towards himself and to look through the hole with one eye into the direction of the Baptizing Chapel. Then the master suddenly lifted a mirror in front of the painting, covering the chapel from the viewer’s sight, and asking loudly enough so that people further away in the crowd could hear: “What can you see, Sir?” “Oh, the Baptistery, Sir Filippo!” the man replied.
The audience was amazed. On the other side of the painting, the chapel was depicted perfectly and the hole was right on the horizon, just at the vanishing point. So the mirror showed just the same as the reality it covered.”