Separate publication, with price "Cinquante Sols" lower right, and the stamp of the Depot de la Marine with initials "R.F." (Republic Francaise, 1792- 1804) either side of an anchor.

First published in 1765, when it was the first French chart to show magnetic variation, in the Atlantic and Indian Oceans. The map represents decades of work by several luminaries of the Enlightenment. The scientific study of magnetic variation was initiated by Edmund Halley and William Dampier, who respectively commanded the first two English scientific voyages to take systematic magnetic bearings at sea. In 1702, Halley first published his world map incorporating data from many sources, and showing "isogonic lines" of equal magnetic value in the Atlantic Ocean. However, as magnetic variation remains in constant flux Halley's chart inevitably became obsolete. In 1744 the Royal Society commissioned two of its members, William Mountain and James Dodson, to collate and compile some 50,000 individual magnetical observations gleaned from the logbooks of Royal Navy and East India Company officers. The project was so complex that both men ultimately conceded they did not believe variation came "under the direction of any one general law".

When Louis Freycinet took command of the corvette 'L'Uranie' he was charged with the investigation of the shape of the earth, terrestrial magnetism, meteorology, and natural science, in order to help determine the sphericity of the earth. Freycinet and his crew measured the magnetism of the earth at three key different locations: Mauritius, Guam (between the Philippines and the Marshall Islands), and Maui in the Hawaiian Islands. He then calculated the degree of flattening for each hemisphere, and at the equator, and concluded that the earth was basically round. It is therefore very likely that Louis Freycinet would have been very familiar with the chart.