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Description

Rare and highly important late 18th Century World map, which provides an overview of the discoveries associated with the variations of the magnetic compass around the world, as first observed by Edmund Halley in 1700, subsequently updated by William Mountaine and James Dodson in 1756 and subsequently agumented by the French Astronomer Guillaume Joseph Hyacinthe Jean Baptiste Le Gentil de la Galaisière in 1765 and thereafter.

Halley's original discoveries created a systematic conceptual mapping of the variations of the magnetic compass at sea, allowing mariners to make navigational adjustments to their compass readings and furthering the science of accurately navigating at sea. As noted in their presentation to the Royal Society on March 20, 1755, it became apparent over time that Halley's observations made in 1700 were only reliable for a certain period of time, after which new observations were required. Mountaine and Dodson began making their observations in 1744 and over the course of the next 11 years, with the assistance of data compiled by the British Royal Navy and others, published an updated set of observations. These observations allowed them to amend and update Halley's original chart of the world, providing the results of the updated observations on the variations of the magnetic compass at sea in frequently used shipping regions and updating in a general fashion the cartographic accuracy of Halley's underlying map.

As a result of the work of Mountaine and Dodson, Halley's chart became a constant work in progress, which was subsequently updated by other scientists. The conception of a variation chart did not begin with Halley. The first such chart was constructed in 1530 by Spanish cosmographer Alonzo de Santa Cruz, from very imperfect observations. More than a hundred years later the astronomer, Halley, undertook, at the expense of the British government, three voyages into the Atlantic for the verification of certain physical data, the result of which was the production of a general variation chart on which the points where the navigator had found the same amount of variation were connected by curved lines.

Dodson and Mountaine of the F.R.S., subsequently constructed their revised chart from more than 50,000 actual observations made in different parts of the world. This variation chart was published and sold Mount and Page at their nautical warehouse on Tower Hill. In the 19th century charts, giving various magnetic elements flourished, with charts made by Sabine, Barlow, Erman, and Horner, as well as others computed according to Gauss' theory of terrestrial magnetism, include one prepared by the Hydrographic Office of the Admiralty in 1858, under the direction of Captain Sir F. J. O. Evans.

The work of Dodson and Mountaine was ultimately published in An Account of the Methods used to describe Lines on Dr. Halley's Chart of the terraqueous Globe, showing the variation of the magnetic needle about the year 1756 in all the known seas, &c. By Wm. Mountaine and James Dodson, was published in 1758.

Condition Description
Flattened and cleaned, with minor restorations.
Laurie & Whittle Biography

Robert Laurie (ca. 1755-1836) and James Whittle (1757-1818) formed their Fleet Street, London-based firm upon the 1794 death of their employer Robert Sayer, himself one of the dominant print and mapmakers of the last half of the 18th century.

Laurie & Whittle started managing Sayer's business as early as 1787. They took over all managerial duties when Sayer's health flagged in 1792, and they changed the imprint in 1794 upon his death. Sayer left the two a 21-year lease on the shop (at £100 a year) and on Sayer's Bolt Court premises, as well as an option to acquire stock and equipment at a preferential price of £5,000 payable over three years.

Robert Laurie retired from the firm in 1812, and his role was assumed by his son, Richard Holmes Laurie (1777-1858). The younger Laurie worked with James Whittle until the latter died in 1818. After R. H. Laurie died in 1858, Alexander George Findlay, FRGS (1812-1875) purchased the firm from his daughters. The firm continues today under another name, specializing in yachting charts.

Laurie & Whittle were prolific print and map publishers, and throughout their careers, they produced numerous very important and rare works. They carried on Robert Sayer's atlas business and were responsible for editions of The Complete East-India Pilot and The American Atlas.