“A New Method of Finding a Ship’s Position at Sea” by Capt. Thomas H. Sumner

On November 25, 1837, American sea captain, Thomas H. Sumner, departed Charleston, South Carolina on a ship bound for Greenlock, Scotland. While en route, he discovered a new methodology in celestial navigation, later eponymously titled, the “Sumner line” or the circle of equal altitude. On December 17th, after days of overcast skies and poor visibility, Capt. Sumner was near the coast of Wales when the sun reappeared through the clouds. He used that opportunity to chart a series of estimated latitudes, and plotted the longitude for each, finally observing that his estimated positions were all located on a single line. Sumner’s calculations (and the resulting voyage) led him to theorize that “a single observation of the altitude of a celestial body determines the position of a line somewhere on which the observer is located.”

Capt. Sumner formally published his findings six years later in 1843. He titled the slim volume, A New and Accurate Method of Finding a Ship’s Position at Sea, by Projection on Mercator’s Chart. The 2nd edition of Sumner’s text arrived two years later in 1845. Sumner’s method received immediate recognition and within the first year of publication, the United States Navy supplied every ship in its fleet with a copy. The 3rd edition went up for sale in 1851, though Sumner’s exact involvement with this later printing is unclear. A year earlier, Capt. Thomas H. Sumner was institutionalized and committed to McLean Hospital, then known as “The McLean Asylum for the Insane.” Sumner was a patient there for fifteen years. In 1865, he entered the “State Lunatic Hospital at Taunton,” where he remained for the rest of his life.

Selina C. Sumner, his wife, was left to care for the couple’s four young children. In 1852, the same year a hospital report certified that her husband’s mental capacities were “no better,” Selina petitioned the U.S. Congressional Committee on Commerce for “A gratuity in consideration of the discovery by her husband, Thomas H. Sumner, of a new method of finding a ship’s position at sea.” The petition asserted that “the fact of the importance of his discovery has been verified by the testimonials of Professor Peirce, of Harvard University, Lieutenant Maury, of the United States navy, and other persons alike worthy of full confidence; all of which testimonials are published in the third edition of Captain Sumner’s work.” It’s possible Selina Sumner was instrumental in the publication of the 3rd edition in 1851, when the financial implications of her husband’s hospitalization became increasingly severe. William Cranch Bond, the founding Director of the Harvard College Observatory, authored the first printed testimonial, where he advocated for the evident success of Sumner’s method and the present need for governmental financial support.

Capt. Sumner, in the language of the petition, was “now himself hopelessly insane… having lost what property was under his control in an early stage of his malady.” What little remained, wasn’t enough to cover his own medical expenses, much less to provide for his family. The earned income from book sales of the earlier two editions amounted to less than four hundred dollars combined which, the petition argued, paled in comparison to the intrinsic worth of the discovery. Capt. Sumner in his “genius and scientific labor” made himself “a benefactor to the navigation interests of his county,” but he had not “enriched himself,” nor was it likely any future sales would ever cover “his personal expenses at the asylum.”

On February 2, 1854, William H. Seward, a representative from the Committee on Commerce, submitted to Congress “A Bill for the purchase of the copyright of a work published by Thomas H. Sumner.” The 33rd U.S. Congress passed and ordered Bill S. 181 to be printed later that July and, in doing so, the federal government purchased the copyright of Sumner’s text for $10,000, a sum which is roughly equivalent to $320,000 today. By the terms of the bill, “the said copyright shall be deemed extinct” upon purchase, “and said book may thereafter be published as if no such right had existed.” A 4th and final printing of Sumner’s text went to publication in 1866.

When Thomas H. Sumner died in 1876, no formal obituary appeared in any Boston newspaper, despite the relative prominence of his family connections and the enduring significance of his own contributions to celestial navigation. In the 20th century, the U.S. Navy named two survey ships after Sumner, the second of which became operational as recently as 1997. Similarly, there is a lunar impact crater on the far side of the moon named for Sumner, and the centennial of his book’s publication prompted the first biographical history of his life. The Wolbach Library houses a copy of the curious 3rd edition of “A New Method of Finding a Ship’s Position at Sea,” published after Sumner was institutionalized but before the federal transferal of copyright.


“A New Method of Finding a Ship’s Positions at Sea,” Boston Mercantile Journal vol. 2, no. 8 (Aug. 24, 1843): 241-42.

Davis, John. In Senate of the United States. February 2, 1853. — Ordered to Be Printed. Mr. Davis Made the Following Report. (To Accompany Bill S. No. 604.) The Committee on Commerce, to Whom Was Referred the Petition of Selina Sumner, Wife of Thos. H. Sumner, Late a Master Mariner, Having Considered the Facts Alleged, and the Proofs Adduced in Support Thereof, Report as Follows. Serial Set no. 671. United States Congressional Serial Set. Washington, DC, 1853.

Richardson, Robert S. “Captain Thomas Hubbard, 1807-1876.” Publications of the Astronomical Society of the Pacific 55, no. 324 (1943): 136-44.

Sumner, Selina C. Petition of Selina C. Sumner, Praying a Gratuity in Consideration of the Discovery by Her Husband, Thomas H. Sumner, of a New Method of Finding a Ship’s Position at Sea. December 14, 1852. Referred to the Committee on Commerce. December 16, 1852. Ordered to Be Printed. Vol. Serial Set No. 670. United States Congressional Serial Set. Washington, DC, 1852.