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Joseph von Fraunhofer (March 6, 1787 - June 7, 1826) was a German optician. One of the most difficult operations of practical optics was to polish the spherical surfaces of large object glasses accurately. Fraunhofer invented a machine that rendered the surface more accurate than it was left by the grinding. He invented other grinding and polishing machines, and introduced many improvements into the manufacture of the different kinds of glass used for optical instruments. In 1814, Fraunhofer invented the spectroscope. He discovered that bright fixed line which appears in the orange color of the spectrum when it is produced by the light of fire. This line enabled him to determine the absolute power of refraction in different substances. Experiments to ascertain whether the solar spectrum contained the same bright line in the orange as that produced by the light of fire led him to the discovery of the 574 dark fixed lines in the solar spectrum. These dark fixed lines were later shown to...