Thomas Hubbard Sumner (20 March 1807 – 9 March 1876) was a sea captain during the 19th century. He is best known for developing the celestial navigation method known as the Sumner Line or line of position. Born in Boston, Massachusetts, Sumner entered Harvard at age 15. In 1829, he became a sailor on a merchantman engaged in trade with China. He "discovered" the line of position on a voyage from South Carolina to Scotland in 1837. As he was nearing the English coast he was uncertain of his position after several days of cloudy weather and no sights. A momentary opening in the clouds allowed him to take a sight of the sun which he reduced with his estimated latitude but, being uncertain about the latitude he reduced the sight again using 10' lesser and 10' greater latitude and he observed that all three resulting positions were located in a straight line which also happened to pass through a lighthouse on the coast. He reasoned that he must be located somewhere along that line and so he set course along that line reasoning that he should eventually sight the light which, in fact he did. He realized that a single observation of the altitude of a celestial body determines the position of a line somewhere on which the observer is located. Sumner published his findings six years later in 1843 and this method of resolving a sight for two different latitudes and drawing a "line of position" through the two positions obtained was an important development in celestial navigation. The method was instantly recognized as important and a copy of the pamphlet describing the method was supplied to every ship in the United States Navy. In 1850, he was committed to the McLean Asylum in Boston. Five years later, he entered the Lunatic Hospital in Taunton, Massachusetts where he died in 1876. Two survey ships in the United States Navy have been named for him, USS Sumner. Also, a crater on the Moon, Sumner (crater) was named for him.
Further reading
- Capt. Thomas H. Sumner, A New and Accurate Method of Finding a Ship's Position at Sea, by Projection on Mercator's Chart, July 1843, Thomas Groom & Company of Boston
