Hand-operated grinding/polishing machine, 1780-1820.
© Science Museum / Science & Society Picture Library
This hand operated grinding/polishing machine was constructed and used by the famous English astronomer, Sir William Herschel (1738-1822). It was employed to shape and polish small speculum (metal) mirrors of around 6-inch (15cm) aperture that were fitted in his 7-foot telescopes. To produce the necessary motions in the machine, it is fitted with offset-pivots, levers and a racket mechanism. This device may be the only complete surviving example of a grinding/polishing machine made by Sir William Herschel.