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The Mapmaker's Mystery

"The Mapmaker's Mystery" (June 2014 Discover magazine image) - RF CafeDo you ever wonder what it is Bright idea - RF Cafethat causes the figurative 'light bulb' to go on over someone's head when a brilliant ideas occurs that solves a perplexing conundrum? Legend has it that Isaac Newton devised his theory of gravitational attraction after getting bonked on the head by an apple. Percy Spence supposedly came upon the idea of using microwaves for cooking food when a chocolate bar in his pocket melted when he stood too close to a poorly shielded magnetron (Percy never fathered anymore children after that, either). George De Mestral invented Velcro while painstakingly picking cockleburs out of his dog's fur. Alexander Fleming discovered penicillin on mold growing in an unattended Petri dish. Dr.s Arno Penzias and Robert Wilson found the cosmic microwave background (CMB) signature in unexplainable 'noise' emanating from every direction in the sky.

Library of Congress' head cartography specialist John Hessler's light bulb came on while investigating how a 15th century portolan map's creator managed to produce a recording with accuracy and detail unequalled by any other within centuries of his own. It was an era predating the Mercator projection method of translating points on a spherical surface into equivalent points on a flattened surface. This particular map of unknown origin depicted hundreds of ports and land details of the Mediterranean region "so accurate that ships today could navigate with it." Mr. Hessler has not yet solved the mystery of who drew the map, but he did uncover a clue as to the means for accuracy.

In his previous life, the chemical engineer and amateur bug chaser exploited a mathematical mapping technique to correlate mutations of butterfly wings markings with theorized ideas regarding species evolution. It facilitated the calculation of energy levels expended in the relocation of spots on the wings. Hessler wondered what might be the cause of slight variations in locations of land masses on the 15th century map as compared to modern maps. Ingeniously, he did a point-by-point mapping and connected the points with straight lines, thereby constructing a grid, to produce the image shown in the included thumbnail (see Discover website for full-size version). What appeared was an apparent rotation across the entire map. It turns out to match exactly with the difference between the Earth's magnetic declination in the previous era to today's value - an 8.5° rotation, to be exact. Hessler applied the same method to other maps and discovered similar congruences based on magnetic declinations of various mapmakers' epochs. This revelation, IMHO could be considered the Rosetta Stone of cartography.

 

 

 

 

Posted  , 2014

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