| 11. | Iceland spar was much used in optical instruments until replaced by synthetic material.
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| 12. | He also made many of the optical instruments employed in sighting the guns.
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| 13. | Many new optical instruments with medical applications were invented during the 19th century.
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| 14. | Radio telescopes collect signals that help fill in gaps left by optical instruments.
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| 15. | Makers of optical instruments need to correct optical systems to compensate for aberration.
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| 16. | Lead glass, which is especially suitable for optical instruments, caused English glassmaking to prosper.
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| 17. | Jonathan Crary argues that optical instruments were more than toys.
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| 18. | He has worked to restore Galileo's optical instruments in Italy.
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| 19. | The Optical Museum Jena shows optical instruments from eight centuries.
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| 20. | Nikon also makes cameras, scanners, microscopes and other optical instruments.
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