Hubert Airy first became aware of his affliction in the fall of 1854, when he noticed a small blind spot interfering with his ability to read. “At first it looked just like the spot which you see after having looked at the sun or some bright object,” he later wrote. But the blind spot was growing, its edges taking on a zigzag shape that reminded Airy of the bastions of a fortified medieval town. Only, they were gorgeously colored. And they were moving.

“All the interior of the fortification, so to speak, was boiling and rolling about in a most wonderful manner as if it was some thick liquid all alive,” Airy wrote. What happened next was less wonderful: a splitting