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Stumper #48.






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A Closer Look

Magnification was almost certainly first experienced many thousands of year ago through a single drop of water lying on a surface. Much later, ancient Greeks and Romans found that looking through glass bowls or spheres filled with water made things look larger - but distorted. You can experiment with this yourself with glass bottles, jars or drinking glasses.

About 800 years ago, reading-stones were invented. A reading-stone was a primitive plano-convex lens made by cutting a glass sphere in half. Over time, it was found that thinner lenses magnify with less distortion and craftsmen began making small magnifying disks of glass, convex on both sides, which were worn as eyeglasses in a frame resting on the bridge of the nose. Because they were used by people who could read and write, these eyeglasses became symbols of learning.

By 400 years ago Galileo had developed special skills in hand-grinding (shaping) and polishing lenses for his 'spyglasses' (refracting telescopes) with which he gained fame by showing never before seen details of the planets. Although Galileo's lenses were the best at the time they were not perfect; they had little bubbles and were a greenish color due to the presence of iron.

Most of us give little thought to the evolution of the modern magnifying lens with the accompanying advances in glass making, grinding and polishing. Modern techniques for making and shaping very fine, clear glass have allowed the development and production of excellent lenses of many shapes and sizes for our eyeglasses, telescopes, cameras, binoculars, and microscopes.

Some very large lenses have been made for refracting telescopes but their size is limited by the fact that they tend to sag under their own weight, thus creating a distorted image. However, another type of telescope has been invented that uses mirrors that are lighter than glass lenses, and since the end of the 20th century it has been possible to put such telescopes into orbit above Earth allowing exciting advancements in astronomy.

Stumper Questions:
1. The telescopes we have put into space are reflecting types, but what natural advantage of being in space might allow a refracting telescope with a large lens to be used without the need to correct for distortion?
2. Magnifying disks of glass derived their name as a result of their shape, which was seen to be similar to the shape of a small food item. What food item was this?
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