When was the parallel rule invented?

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    P. H

      Single large-scale charts, not bound up in a neptune, appear to have become commonplace by 1800. These let you do chartwork, plot courses, and fix your position with range and bearing. You can prick off Lat and Long with a divider, and draw ranges with a compass. Drawing bearings and measuring courses usually require some sort of scaled arc or protractor – slightly more complex.
      Throughout the twentieth century, the two common ways of achieving this was by shuffling together the parts of a diagonally halved square, or by using parallel rulers. Who invented parallel rulers? Has anyone a nineteenth century citation – perhaps alongside a portrait, or listed in a catalogue or almanac?
      Paul Hughes


        The parallel rule has a long history, being invented in 1580s by an Italian mathematician, Fabrizio Mordente. Not in common use by maritime navigators until the C18th, the earliest example at the NMM being of 1725.
        The rolling parallel rule, familiar from navigation training at Dartmouth (I still have my issue) was invented surprisingly early, in 1771 by Eckhardt.
        As to single-sheet charts of relatively small areas of coastal waters, unbound, these were common as early as navigation itself. Luis Texeira’s Carta de Dobre y Cales dating from 1587 is a good example of a relatively small-scale sea-chart of coastal waters.
        Cook’s large-scale oceanic charts and small-scale inshore charts were always printed as single sheets and issued as such (including his 1759 chart of the St Lawrence, whose original engraved copper printing plate can be seen at the Admiralty Library). Admiralty Hydrographic Office charts were not available a individual sheets for sale to the public until the 1820s.

        It was the bound pilots of small-scale charts (“neptune” is a very archaic term) which came later, generally from c.1670, although bound copies of Spanish charts are found in the Escorial collection (a copy of Pacific coastal charts exists at Greenwich, captured in the 1580s).

        These would not have been for practical use at sea, being bound for presentation to the monarch or rich and influential collectors.
        Justin Reay

        M. K. Barritt, RN.

          Issues of development of marine cartography in response to instrumental technology are touched on helpfully by Susanna Fisher on page 10 in her important book ‘The History of the Blueback Charts’. I have also discussed this in my recent book ‘Eyes of the Admiralty’ (NMM, May 2008), especially on pp. 33-4.
          It does seem to me that research is needed into the emergence of ‘chartwork’ as taught in the Royal Navy i.e., as I put it in my book: the use of a chart ‘to plot a continuous record of past and projected movement as became the drill in the fast power-driven warships of the late nineteenth century’.
          The essentials are there in chapter XVIII of the 1914 edition of the Admiralty Manual of Navigation, especially Article 180, and may be drawn from the superseded ‘Notes bearing on the Navigation of H.M. Ships’, which I have not sighted.
          It is worth noting that whilst Captain Hurd promoted the supply to the Fleet of linen-backed single sheet charts in boxes, he also offered the charts bound e.g. ‘Channel Atlas’ and ‘Mediterranean Atlas’, which remained on offer in the first Admiralty catalogues in the 1820s. Clearly some conservative users were not persuaded by the facility of the single sheet, and this surely reflected the way they used a chart – for reference, not for plotting and measurement.
          As a well-drilled and indoctrinated RN officer, I remember watching with interest mixed with concern, the practice on some MN bridges, even in the first decade of this century. It was clear to me that the chart remained just another reference document rather than a plotting surface. Perhaps this slightly provocative last remark will produce some valuable colloquial evidence on this interesting topic!
          <b.Mike Barritt


            As a retired shipmaster perhaps I may be permitted a brief word in defence of MN’s use of charts.
            During my time deepwater in the Port Line (1958-68), it was custom and practice to plot a position at short and regular intervals when in coastal waters and to plot occasional Dead Reckoning positions and all celestially-derived positions when mid-ocean. However, occasional access to hired Decca coastally and limited use of RoDF stations apart, we had no access to modern electronic nav-aids.
            Later, even in the short-sea ferry trade, my standing orders and later our Fleet Regulations, required positions to be plotted on a chart surface at short and regular intervals – albeit using a chinagraph pencil on a locked down perspex chart cover. I suggest that the agreed bad practice recently observed by the previous correspondent derives from some younger officers’ over-reliance on electronic charts and schematic navigation displays – a practice which I also deplore.
            In short, as in the RN, MN best-practice remains regular plotting and recording of positions on the chart – where possible these being derived from more than one source.
            James W Martin


              Judging by the date, the Mr Eckhardt who was mentioned by Justin Reay as the inventor of the parallel ruler was Anthony George (Antoine Georges) Eckhardt, who was born in the Netherlands about 1740 and died, probably in England about 1810.
              He seems to have been an ingenious chap, having also invented pumping machinery to drain the polders, and a geared capstan, devised by him, was installed in HMS Defiance about 1780. This was the predecessor the Phillips Capstan, which worked on the same principle, and was installed in many British warships. There is a model of Eckhardt’s machine in the basement at the NMM, but I don’t believe it has ever been exhibited. He became a Fellow of the Royal Society.
              See: Nautical Research Journal Vol 43, p.188-190 and Captans and Windlasses: An Illustrated History of the their use at Sea, p. 96.
              John Harland


                There is a foreign word for it: “marquois”, apparently a blunder for marquoir, French for marker.
                Charles Dawson


                  In the discussion on the parallel rule I mentioned that (according to my Concise Oxford Dictionary dated 1964) this is called marquois: “a blunder for marquoir, marker”.
                  My COD seems to have confused this with the marquois scale, a proportionately-divided ruler for use when drawing items to scale, and in ssurveying, named after its inventor Thomas Marquois who established a Military Academy in 1762 at Newlands 2 miles from London (Holland Park district) and introduced his scales in 1783.

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