Page:Williamherschel00simegoog.djvu/139

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THE REFRACTOR AT DORPAT
127

space than ever human being did before me. I have observed stars, of which the light takes two millions of years to travel to this globe.'" The Church is a telescope that looks, or should look, even farther into space and time.

While Herschel was giving life and power to the reflecting telescope, Dollond's followers in this country and Fraunhofer in Germany were restoring the refractor to the place from which it had been deposed. In 1825 the finest refractor that, up to that time, the world had ever seen was erected for Struve at the expense of the Russian Government in Dorpat. The tube was 13 feet in length, and the object-glass was 9 Paris inches in diameter. The weight of the whole was about 3000 Russian pounds. Of his first look through it Struve says: "I stood astonished before this beautiful instrument, undetermined which to admire most, the beauty and elegance of the workmanship in its most minute parts, the propriety of its construction, the ingenious mechanism for moving it, or the incomparable optical power of the telescope, and the precision with which objects are defined"[1] He was proud of his assistant. He believed it to be the equal of Herschels 40-feet reflector, and it was certainly far more easy to work. With its help he continued the work Herschel began. It appears, however, that Herschel sometimes used a parabolical glass mirror of 7-feet focal length instead of the metal mirror,[2] avoiding by reflection the colours due to refraction. This should be remembered to his credit.

  1. Astronom. Trans. ii 94.
  2. Phil. Trans.for 1803, p. 228.