Chart of the variation of the magnetic needle For all the known Seas comprehended within Sixty Degrees of Latitude North and South: with a New and Accurate Delineation of the Magnetic Meridians, accompanied with suitable Remarks and Illustrations, by Thomas Yeates. Drawn & Engraved by J. Walker. To the Right Honourable The Master, the Deputy Master, Wardens and Elder Brethren of the Corporation of Trinity House, of Deptford Stroud. This Chart, honoured with their Munificent support is by Permission, most respectfully Dedicated, By their Most Humble and most obliged Servant the Author.

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.