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1843 - Sumner’s Method of Celestial Navigation

  • Luc CHAMBON
  • Apr 22
  • 2 min read

Updated: Jul 7

Sumner's Manual
Sumner's Manual

Captain Thomas Hubbard Sumner publishes a New and Accurate Method of Finding a Ship’s Position at Sea.

This is the fruit of his thinking after the revelation of the line of potential positions he had in 1837 while drifting aboard the Cabot.

His idea is quite simple, very practical, and accessible to all – brilliant in a single word. He proposes :

  • to take a first measurement of sun altitude at Time T1 ;

  • to choose two arbitrary values of latitude around the supposed one, and to work out the two corresponding positions ; to draw the line of positions as he names it, which will become the Sumner’s line for his readers, which passes by the two calculated positions ;

  • then to take a second measurement of sun altitude at Time T2 ;

  • to choose two arbitrary values of latitude once again ; to work out the two positions and to draw a second Sumner’s line ;

  • ideally, to take a third measurement of sun altitude at Time T3 ;

  • to choose two arbitrary values of latitude once again; to work out the two positions and to draw a third Sumner’s line ;

  • finally to translate the two first lines by the ship course between the measurements ;

  • the intersection of the three lines defines a small triangular area in which lies the position of the ship.

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LINK WITH A PREVIOUS CHRONICLE

1837 - A Fortunate Incident of Navigation

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IN RETROSPECT FROM TODAY

NOTE - On the method fate.

The method makes a splash. Sumner’s pamphlet is delivered on every ship of US Navy.

A French naval officer, Adolphe-Laurent-Anatole Marcq de Blonde de Saint-Hilaire (†1889), then aged 41-43, will improve Sumner’s method in three steps, between 1873 and 1875. He publishes in turn three major articles : Determination d’une Droite de Hauteur par une seule Observation, then Calcul du Point Observé. Point Moyen donné par Trois Observations, and finally Calcul du Point Observé. Méthode des Hauteurs Estimées, by which his method becomes famous and universal.

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SUGGESTED BIBLIOGRAPHY

Thomas H. Sumner – New and Accurate Method of Finding a Ship’s Position at sea by Projection of Mercator’s Chart – Boston, 1843 - available on the Internet

W. A. Mason - Marcq Saint-Hilaire : Father of the New Navigation - US Naval institute, Annapolis, 1939

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