Plan and section of surveying instrument, 1799.
© Science Museum / Science & Society Picture Library
Engraving showing: plan of the instrument; section of the Instrument at right angles to the former, where the upper telescope, with the level for altitudes attached to it are nevertheless represented in elevation; section of the Instrument through the microscopes, and in the direction of the axes of the telescopes. The Principal Triangulation of Britain was carried out by General William Roy of the Royal Engineers between 1787 and 1789, using theodolites designed and built by Jesse Ramsden (1735-1800). Illustration from the first volume of 'An account of the operations carried on for accomplishing a trigonometrical survey of England and Wales' by William Mudge (1762-1820), published in London in 1799.