Rare Survival -- Navigational Aid at Sea with Pricking Marks
Rare, separately-published Norie world map on a Mercator Projection, the preferred projection for tracking voyages at sea.
The present example includes the routes of several voyages, which stretch around the world though the Pacific Ocean, Indian Ocean and Atlantic Ocean, including a curious visit to what appears to be both sides of the future Panama Canal (not completed until 1914).
The geography of the world in minutely recorded, showing the detail achieved by the world’s various hydrographic bodies to this date. One of the only unfinished coastlines is in Antarctica, where scattered peaks and ice islands are shown. A few points in the far north of Canada are also only vaguely drawn; the area was the major focus on many nineteenth-century voyages thanks to the ever-tantalizing search for the Northwest Passage.
As noted below the title, the map was available in separate sheets. A navigator could buy the entire world set or just a section with specific routes/areas, depending on their needs. This set has been joined and would fold neatly, making it easy to carry on long voyages. A note below the title states:
GREAT CIRCLE SAILING and COMPOSITE TRACKS
On this Chart the Great Circle and Composite Tracks are laid down to those parts where such sailing is most practicable; against the Monsoons it is not available, excepting perhaps Steamers; & near to the Equator it becomes as Plane Sailing on the Mercator Chart.
A great circle track indicates the shortest distance between two points on a sphere, and therefore the most direct route. A composite, or modified great-circle, track consists of an initial great-circle track from the point of departure with its vertex on a limiting parallel of latitude.
Dead reckoning and pricking maps
When not navigating with celestial navigation, or in conjunction with it, mariners could estimate their position on a journey via dead reckoning. With dead reckoning, the navigator finds their position by measuring the course and distance they have sailed from a previous point. This is marked on a chart over several days, creating a running record of location at sea. Thus, effective dead reckoning depends on accurate, well-made instruments, as well as on correct calculation and recording by the mariner.
The speed of the ship can be measured using a lead and line and/or the ship’s instrumentation, depending on the ship’s type and technology. A magnetic compass will tell the heading, or direction, of the ship; the compass was invented in China and has been in use in Europe since at least 1183.
Once the speed and heading are known, and the time of travel is also known, the mariner can calculate the distance traveled in which direction. Starting from a known point, the navigator measures out his course and distance from that point on a chart, pricking/dotting the chart with the tip of a pair of dividers to mark the new position. Each day's ending position would be the starting point for the next day's course-and-distance measurement.
Dead reckoning would be only one of a variety of techniques available to the navigator in the mid-nineteenth century, when this chart was made. They would have also been able to take celestial navigation observations using intricately-made instruments, as well as consult tide, wind, and lunar distance tables. Dead reckoning would be used in addition to and in conjunction with these methods, making the routes marked here the best guess of the mariner.
We note a few institutional examples of the map with dates between 1854 and 1871, although several appear to be incomplete sets, lacking one or more of the sheets.
The survival of a complete set with manuscript additions is very rare.