The brilliant Christiaan Huygens needed glasses

He was perhaps the greatest Dutch scientist of all time. Christiaan Huygens (1629-1695) made important contributions to mathematics and physics, he invented the pendulum clock, discovered Saturn’s moon Titan and explained why this planet looked so strange through the telescope . Saturn had no handles as, for example, Galileo thought. According to Huygens, it was a ring.

Together with his brother Constantijn he dragged his own lenses and also built his own telescopes. These lenses were of impeccable quality, but the telescopes were less than optimal. The ratios between the power of the lenses and their distances were not quite correct. This was not due to his technical or mathematical acumen, but to his eyes. Huygens was myopic, writes astrophysicist Alex Pietrow in the newspaper Notes and recordings: The Royal Society Journal of the History of Science.

Although Huygens himself developed a theory on the nature of light (which is still valid), knowledge of lenses and their refraction was still limited in the 17th century. There were no formulas to calculate the ideal distance between the objective and the eyepiece of a telescope.

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

But yes, writes Petrow. If your eyes need lens correction, these formulas are no longer correct. He then deduces from the imperfection of the telescope how badly Huygens must have seen. He could no longer see clearly at a distance: what someone else saw clearly at a distance of seven meters, Huygens could only read from a distance of two meters. In other words, Huygens was myopic.

He had needed glasses with a prescription of -1.5. It’s not a lot. According to Pietrow, such a deviation was not problematic in the 17th century. “Even if Huygens was aware of the defects in his eyesight, he would not have needed glasses. It also played no role in the manufacture of the telescopes. He therefore probably unconsciously included this eye defect in his creations.

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