Hydrography: A Note on Eighteenth-Century Methods

By G N D Evans, published August 1966


A report to Admiral Colville from Joseph DesBarres, compiler of the chart collection named Atlantic Neptune, provides valuable evidence of hydrographic methods he adopted off Nova Scotia in the 1760s. From an onshore baseline of 350 fathoms, theodolite bearings were extended by triangulation to offshore islands and plotted on paper. Equipped with copies, vessels of appropriate sizes charted details of the coast, positions of rocks, and soundings of the depth and nature of the seabed. DesBarres experimented with measuring distances across the sea with 100 fathoms of line deployed successively, and apologised that he still had to report on currents and tides.

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Filed under: Atlantic | Other (Eighteenth C)
Subjects include: Science & Exploration

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