Glasses to correct for eyes that focused incorrectly were well known in George Biddell Airy's time. Myopia, the condition in which the eye focuses short of the retina, leading to poor focus for distant objects, could be corrected by wearing concave lenses; hyperopia (far-sightedness), the opposite condition, was corrected by convex lenses. However, astigmatism, the condition in which the shape of the cornea is not symmetrical, causes the focus to be confused and irregular and cannot be corrected with a simple lens.

Airy's eyes were decidedly astigmatic, the left eye being especially so. In the 1820's, while he was exploring various properties of light, it occurred to him that he might be able to invent a way of correcting for astigmatism. In August, 1824, he carried out several experiments on his eyes that allowed him to deduce the shape of the cornea of each eye. With his knowledge of the behavior of light rays, he was then able to design a specially shaped lens (called a cylindrical lens) that would compensate for the nonsymmetrical shape of the cornea. When he ordered these lenses to be made, they were found to be effective, and he wore them from then on. He was said to carry several pairs of glasses in his pockets in case of emergency.

Unlike some of Airy's inventions, the discovery of astigmatism-correcting lenses was not one that he discussed much in his autobiography, which otherwise gives extensive and self-satisfied details about his many accomplishments. There are only two sentences about this discovery. He says, "On August 25th I made experiments on my left eye, with good measures, and on Aug. 26 ordered a cylindrical lens of Peters, a silversmith in the town, which I believe was never made. Subsequently, while at Playford, I ordered cylindrical lenses of an artist named Fuller, living at Ipswich, and these were completed in November, 1824."

Although he gave it little notice in his writings, the invention of astigmatism-correcting lenses was without doubt one of Airy's most important inventions. Basically the same design has been used for eyeglasses for millions of people and for nearly two hundred years.

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