Newtonian reflecting telescope, 1783-85.
© Science Museum / Science & Society Picture Library
This reflecting telescope was made by the famous English astronomer Sir William Herschel (1738-1822) for his good friend Dr Watson, whom he first met in Bath. The telescope has a 7 foot mahogany tube and stand that is operated using pulley ropes and gears. The heart of the telescope is a 6 1/8-inch mirror made of speculum metal, a bronze alloy with arsenic added for a more reflective surface. Herschel ground and polished all his own mirrors and lenses and then had them built into telescopes which he sold to supplement his income as royal astronomer to King George III (1738-1820). His patron purchased several instruments, while the King of Spain ordered a massive telescope with a 24-inch mirror.