Line of Position Navigation

While nearing land on his way to Scotland in 1837, Captain Thomas Sumner of Boston had an insight that made an enduring contribution to navigation.

Cloudy weather permitted only one sighting on the Sun. With that limited information, Sumner made three different calculations based on estimates of his latitude. Plotted on a chart, the results lay along a straight line. He realized that any ship seeing the Sun at the same altitude in the sky must be located somewhere on that line. This was confirmed by sailing along that course until a lighthouse was sighted on the coast.

Sumner published his method for determining what was later called a “line of position” in 1843, and it became standard practice. 

Caption:
In 1837, Captain Thomas Sumner of Boston devised what would become "line of position" sailing.
Type: Illustration
Image Date: 2012
Credit: National Air and Space Museum, Smithsonian Institution
Origin: National Air and Space Museum, Smithsonian Institution
Creator: Ashley Hornish
Navigators & Inventors
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In 1837, Captain Thomas Sumner of Boston devised what would become "line of position" sailing.