(1) "On the present Situation of the Magnetic Lines of equal variation, and their changes on the Terrestrial Surface" in the Philosophical Transactions, 1833. AND (2) "On the Errors in the Course of Vessels, Occasioned by Local Attraction; With Some Remarks on the Recent Loss of His Majesty's Ship Thetis" in Philosophical Transactions (1831)

BARLOW, Peter TWO papers. (1776-1862, FRS 1822). (1) "On the present Situation of the Magnetic Lines of equal variation, and their changes on the Terrestrial Surface" in the Philosophical Transactions, 1833, (Read May 9, 1833) pp 667-673 (verso of 673 is blank). Two large folding maps, with the larger world map evidently recognized as rare, with one mapseller calling it "unobtainable". This issue is complete in itself and has been disbound from a larger bound volume. Nice, crisp copy. The maps are both in G/VG condition. [++] Barlow contributed to the understanding of the Earth's magnetic field by mapping the lines of equal magnetic variation (isogonic lines). This work helped establish a clearer picture of how magnetic properties vary across different geographical regions. The two maps published in this paper illustrated the lines of equal magnetic variation (isogonic lines) across different regions. This was crucial for visualizing how magnetic declination changes geographically. His work on magnetic lines of equal variation provided crucial insights into how magnetic declination affects compass readings. Understanding this variation was vital for navigators, especially when determining their longitude at sea. "These maps provided essential information for navigation, allowing sailors and explorers to correct their compasses and improve navigational accuracy, which was vital during the age of exploration."--ChatGPT [++] The two maps as called-for in the text: (1) "A Chart of Magnetic Curves of Equal Variation by Peter Barlow" 1833. Large, lovely, folding map of the world, 36"x18". VG condition. And (2): "A Chart of Magnetic Curves of equal Variations in the Northern Regions, 1833. Collated and Arranged by Peter Barlow." 16.5"x18" (Polar view of the Northern Hemisphere). VG condition. [++] PLUS a second, related (and earlier) paper: Peter Barlow, "On the Errors in the Course of Vessels, Occasioned by Local Attraction; With Some Remarks on the Recent Loss of His Majesty's Ship Thetis" in Philosophical Transactions, 1831, pp 215-221. This issue is complete in itself and has been disbound from a larger bound volume. Nice, crisp copy. GOOD/VG condition. "Peter Barlow's 1831 work, "On the Errors in the Course of Vessels Occasioned by Local Attraction," is indeed significant in the history of navigation and magnetism. In this paper, Barlow investigated how the magnetic fields of iron-laden ships could distort compass readings, leading to navigational errors. He noted that the increased use of iron in ship construction, including iron ballast, tanks, and capstans, created substantial magnetic masses that affected compass accuracy. For instance, in His Majesty's ship Gloucester, the deviation in the east and west points was found to be 9°30' in the British Channel, meaning the vessel could be over a mile and a half off course after ten miles. Such errors, if unrecognized, could result in significant navigational mishaps, especially in narrow channels or during nighttime voyages. This research was particularly pertinent following the loss of His Majesty's ship Thetis, underscoring the practical implications of Barlow's findings. His work contributed to the understanding of how local magnetic influences could impact maritime navigation, leading to advancements in compensating for these errors and improving the safety and accuracy of sea voyages."--Royal Society Publishing online.…