If The Cathedral Wavers . . .

The Cathedral of Florence has a dome built by Filippo Brunelleschi (1377–1446). The builder left a small opening in the dome through which a shaft of light streams every June 21. The sunbeam illuminates squarely a brass plate set in the floor of the sanctuary. Should the ray fail to cover the plate completely or should there be any other divergence it would be considered a signal of alarm. It would indicate that the structure had shifted its center of gravity, and steps would be taken to deal with the emergency. The cathedral is considered to stand on marshy ground and wheeled traffic is forbidden in its immediate vicinity.