Joseph Ritter von Fraunhofer (March 6, 1787 - June 7, 1826) was a German physicist. One of the most difficult operations of practical optics was to polish the spherical surfaces of large object glasses accurately. Fraunhofer invented a machine which rendered the surface more accurately than traditional grinding. in 1814, he invented the spectroscope. In the course of his experiments he discovered the 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 afterward 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 574 dark fixed lines in the solar spectrum. These lines are called Fraunhofer lines in his honor. Like many glassmakers of his era who were poisoned by heavy metal vapors, Fraunhofer died young, in 1826 at the age of 39. His most valuable glassmaking recipes are thought to have gone to the grave with him.