“‘Do you know who first explained the true origin of the rainbow?’ I asked.

‘It was Descartes,’ [Richard Feynman] said. After a moment he looked me in the eye.

‘And what do you think was the salient feature of the rainbow that inspired Descartes? mathematical analysis?’ he asked.

‘Well, the rainbow is actually a section of a cone that appears as an arc of the colors of the spectrum when drops of water are illuminated by sunlight behind the observer.’

‘And?’

‘I suppose his inspiration was the realization that the problem could be analyzed by considering a single drop, and the geometry of the situation.’

‘You’re overlooking a key feature of the phenomenon,’ he said.

‘Okay, I give up. What would you say inspired his theory?’

‘I would say his inspiration was that he thought rainbows were beautiful.’”

—Leonard Mlodinow, Feynman’s Rainbow, 2003.