[logfromblammo]

Seems like it would have been trivial to put a filter in front of the upper mirror of a sextant during daylight hours to avoid this. I know that the sextant was an optical device that became commonly used after Newton's Opticks was published, and that Newton temporarily blinded himself while researching it, so there might have been an inkling among the educated that staring directly at the sun was dangerous. But I don't know whether optical filters were known then, or came into use later, as adjuncts to photography. It's definitely too soon for arc welding.