The brilliant Christiaan Huygens needed glasses

He was perhaps the greatest Dutch scientist ever. Christiaan Huygens (1629-1695) made important contributions to mathematics and physics, inventing the pendulum clock, discovering Saturn’s moon Titan and explaining why the planet looked so strange through a telescope. Saturn did not have handles, as Galileo thought, for example. According to Huygens, this was a ring.

Together with his brother Constantine, he hauled his own lenses and also built his own telescopes. Those lenses were of impeccable quality, but the telescopes were far from ideal. The ratios between the power of the lenses and the distances between them weren’t quite right. It wasn’t because of his technical or mathematical insight, but because of his eyes. Huygens was nearsighted, astrophysicist Alex Petro wrote in the journal Notes and Records: Journal of the Royal Society for the History of Science.

Although Huygens himself had developed a theory about the nature of light (which is still valid), knowledge about lenses and their refraction was still limited in the seventeenth century. There were no formulas for calculating the ideal distance between the objective and the eyepieces of the telescope.

Huygens’ writings show that he started with a set of lenses from which he knew the ideal distance. He then calculated what a much larger telescope he wanted should look like – those formulas were there.

But yes, Pietro writes. If your eyes need lens correction, these formulas no longer hold true. Then he deduces from the defects of the telescope how bad Huygens’ vision is. He could no longer see clearly at a distance: what another person saw clearly at a distance of seven meters, Huygens could only read at a distance of two meters. In other words, Huygens was shortsighted.

He required prescription glasses of -1.5. That’s not much. According to Pietro, no such deviation was an issue in the seventeenth century. “Even if Huygens had been aware of the deficiencies in his eyesight, he would not have needed spectacles. This also played no part in making telescopes. So he may have unconsciously included this eye defect in his designs.”

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