F3935-1

Bell machine, movement Long Caption: Telescope bell machine (or 'zone clock') made by Alexander Herschel and used by William Herschel with his 40-inch telescope. Bell machines were designed to solve a problem William Herschel encountered as he used his 20-foot telescope for ‘sweeping’ for nebulae, directing the instrument to the south and examining the heavens as they drifted past. The method of sweeping for nebulae that William adopted in December 1783 required the workman to raise the tube to the required altitude, and then to raise and lower it in a succession of up-and-down motions that traversed the ‘zone’ under examination. Credit line: © National Maritime Museum, Greenwich, London, Herschel Collection Object: ZAA0658 Artist: Johann Alexander Herschel Date: circa 1790 Medium: metal Size: 390 mm x 285 mm x 150 mm Click here to buy a bespoke print of this image.