The text panel to the left hand side of the chart, written by Thomas Yeates, contains a brief history of the knowledge of magnetism from its discovery by the Chinese "more than a thousand years before the Christian Era", to the discovery by Columbus of "the Variation of the Compass in his Voyage to America, in the Autumn of 1492, before which period it was thought the Needle at all places pointed due North". Its systematic charting would not start until the seventeenth century when Dutch seamen under the orders of Prince Maurice were ordered to "observe and register the Variation in all places". Finally, researches into magnetic variation whilst "steering a ship at sea", were undertaken by Captains Cook and Flinders. Flinders' findings are expanded upon and explained in detail in Yeates' text.

Yeates further explains the history of 'Variation Charts', with Edmund Halley's famed chart of 1701 highlighted as the template for all the subsequent charts produced throughout the eighteenth century. Yeates goes on to state that the current chart improves on the 'Halleyan System', which only covered the Atlantic and Indian Oceans, with the "delineation of the Magnetic Meridians, shewing as well geometrically as numerically the Quality of Variation for all the known seas within the limits of Sixty Degrees of Latitude north and south of the Equator, including the whole extent of the Pacific Ocean with geographical improvements according to the latest authorities". Finally, Yeates gives a brief explanation on how to use the magnetic variation lines that appear on the chart.

Thomas Yeates (1768-1839) was an orientalist and scholar, who wrote extensively on Indian, Middle Eastern, and Biblical history. One might assume an orientalist to be a rather unusual choice for the authorship of such a chart, and he admits as much by acknowledging the help of Captain Hurd of the Royal Navy and Hydrographer to the Admiralty and Captain Horsburgh, Hydrographer to the East India Company.

We were only able to trace two institutional examples of the first edition: one in the British Library and the other in the National Maritime Museum. The chart was subsequently republished by J.W. Norie & Co. in 1824, with the only institutional example we could trace of that being held in the National Library of Australia.

Provenance: book plate of Michael Morrah, who practiced as a surgeon in Worthing during the first half of the nineteenth century.