Troughton's circle, 1817.
© Science Museum / Science & Society Picture Library
Print of 'Troughton's Circle', an astronomical instrument. The engraving, taken from 'Rees Cyclopedia' published 1812-1820, shows an instrument built and designed by the London instrument maker, Edward Troughton (1753-1835). The universal instrument, housed in an observatory, was used measure the position of the stars, planets and Sun wherever they lay in the heavens. Unlike transit instruments, Troughton's circle was not limited to making measurements in the north-south meridian.