The Dutch astronomer Christian Huygens (1629 - 1695) used a telescope 123 feet long. In 1673, the German astronomer Johannes Hevelius (1611 - 1687) used one that was 150 feet long. In 1722, the English astronomer James Bradley (1693 -1762) used one that was 212 feet long.
In 1757, thirty-one years after Gulliver's Travels was published, optical advances made achromatic parabolic lenses possible, and long telescopes vanished. Comparatively short telescopes of better magnification, like those of the Laputans, came into existence. Swift did not live to see it, but he was correct in his prediction.