| Description | Discusses the ‘cross’, refers to Humboldt saying ‘he had been able to know the hour of the night from the position which the cross occupied in the heavens’, and Rumker proposes directions for this. Includes a table titled ‘numbers for the days’ and describes how to use the table, referring ‘to the number against the position of the cross. Discusses the ‘observations of the variation and dip of the needle’. Includes a table depicting latitude, longitude, observation from 15 feet elevation, sun’s magnetic azimuth, variation, and place of the compass and ships course. Refers to observations taken in a ‘vessel in the heavy sea’, reversing the compassing during observations. Refers to observations Rumker made with [Thomas] Brisbane in 1821. Includes a table of ‘observation of the variation of the needle made on a passage from England to New South Wales’ in 1821. Includes a table depicting ‘inclination or dip of the needle observed on a passage from Rio de Janeiro to New South Wales by’ [Rumker] in his ‘cabin on the starboard side’. Discussion regarding currents and nautical remarks. Refers to the advantages of chronometers. Refers to a table of ‘uncertainties’ regarding Jupiter, Venus, Mars, and Saturn. |