Bowen's map on Mercator's projection was also issued in 1744-8 together with his double hemisphere map and used in the same publications, namely his atlas and John Harris's "Travels and Voyages". However, unlike the double hemisphere, this is a far more scientific document. Its major emphasis is on the sea and marine travel. Major geographical detail is confined to the coast while the map attempts to show the curves of magnetic variation as read on a compass. This was a navigation theory that was prevalent in the 17th and 18th century. It was believed that a compass will always align itself to the magnetic north, no matter where one was. Once a large collection of readings was collected, it would provide far greater accuracy in establishing the exact positions of a ship. Unfortunately, unknown to the researchers of the period, these readings were almost always corrupted by nearby metal since in reality, magnetic compass readings will align to the closest magnetic fields.



As with the double hemisphere, the map draws most of its geography from French maps of the period. The Pacific Northwest coast is left as unknown with a strong suggestion of an inlet showing the Strait of Anian, a persistent legend of the western entrance to the Northwest Passage. Russian exploration of the east coast of Asia is shown. The body of water north of Japan is again marked as the "Sea of Corea" (Korea) and the mysterious and mythical Gamaland is still present albeit in a far diminished form.



In the far North Atlantic, the nature of Greenland is left unknown as was common on maps but Bowen speculates about Svalbard, calling it "Spitsbergen or Greenland" suggesting that it was an undiscovered part of Greenland. Just off Svalbard's eastern coast is "Witches Island" now modern Edgeoya, named after its discoverer, the English merchant Thomas Edge.



Finally, a panel of text on the lower left states that for a greater amount of detail on the lines of curvature one should consult the map published by Mount and Page, which was almost certainly the map the Bowen himself used as one of his sources.


Our example offered for sale is a 1766 edition. [WLD3889]