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Telescopes were first constructed in the Netherlands about 1608. In 1853 Alvan Clark, of Cambridgeport, Mass., a comparatively unknown portraitpainter, after having experimented from 1846 in grinding lenses, succeeded in turning out a glass superior to any made elsewhere in the world. He and his sons went on making large and larger instruments, till they ground the 36-inch telescope for the Lick Observatory, in California, and the son, Alvan G., made the 40-inch Yerkes telescope for the observatory of the University of Chicago, erected at Williams Bay, Wis. The movable part of the latter, which turns on the polar axis, weighs about 12 tons, and the clock weighs 1 1/2 tons. The refracting telescopes of the Naval Observatory, at Washington, 33 feet long, and at the Leander McCormick Observatory, University of Virginia, both made by Alvan Clark & Sons, have a 26-inch aperture. The largest reflecting telescope in the United States is at Harvard University, 28-inch mirror. Other notable telescopes are at Princeton University (Clark, 23-inch); Rochester, N. Y. (Clark, 16-inch); Madison, Wis. (Clark, 15.5-inch); Dudley, at Albany, N. Y. (Fitz, 13-inch); University of Michigan (Fitz, 12.5-inch); and Middletown University (Clark, 12-inch).

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