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Description: | Navigators use parallel rulers for laying off a specific course on a chart. They were first invented in 1584 by a Frenchman named Mordente, but only became common in navigation in the 18th century.
Captain Feild's (or Field's) design had one of its outer edges divided into degrees like a protractor, with the opposite edge divided into points, half-points and quarter-points (of the compass). This made it easier to read off the bearing of a line than with a plain parallel rule, which had to be moved across the chart to the nearest compass diagram. This example has two inscriptions: 'CAPTN. FIELD'S IMPROVED' and 'REGD. NO. 3549 JANY 1854'. The registered design names the maker as J.D. Potter, then working at 31 Poultry, London, although no maker's name is given on this example.
Ex DI.133.
caption: Parallel Rule | Publisher: | "http://collections.rmg.co.uk/" | Rights holder: | "Royal Museums Greenwich" | Subjects: | parallel rules | Source: | Royal Museums Greenwich | Identifier: | http://collections.rmg.co.uk/collections... | Go to resource |
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