Elisabeth Paul Edouard Rossel letter to Louis Marie Bajot concerning the lunar method for calculating longitude, 15 June 1819

MLMSS 9789

fonds

1819

1000558

0.05 metres of textual material (1 folder) - manuscript

In this letter, written in French, Rossel writes to Louis Marie Bajot, inspector-general of the library of the Ministry of the Marine and editor of the Annales Maritimes et Coloniales. In response to the articles Bajot has asked him to review, Rossel recommends that the lunar method be abandoned since the difficulty of accurately measuring the height of the moon is too great and liable to "grandes erreurs". By the time Rossel wrote this letter, in 1819, the marine chronometer, pioneered by John Harrison and tested on Cook’s second Voyage, was becoming widely accepted as providing the most accurate method of measurement.

The content of this letter of 1819 reflects Rossel’s changing view on methods for calculating longitude. Rossel had worked extensively with the lunar method, but states in this letter that he no longer believed it to be a viable method of measuring longitude at sea. The letter demonstrates that Rossel’s opinions were held in high regard as his reviews of contemporary works on longitude had been sought by the Ministry of the Marine.

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