A TECHNOLOGY PAST ITS LIMIT by Jeff Hecht Great Paris Telescope The Lesson of the PUBLIC DISPLAY The Paris Exposition Universelle of 1900 was meant to be the grandest world's fair of all time, and the Great Paris Telescope was one of its most impressive exhibits. A siderostat mirror followed the turning sky and directed light into a 49ΒΌ-inch f/48 refractor, fixed horizontally. Two objective lenses were made, one for visual and one for photographic use. During daytime the Sun could be projected onto an enormous indoor screen in a darkened auditorium, as in the drawing at top. 28 J U L Y 2 0 1 7 * SK Y & TELESCOPE