. A new treatise on the practice of navigation at sea : containing all the details necessary to enable the mariner to become a good practical navigator. . but this is seldom necessary at Sea. QUESTIONS FOR EXERCISE Question let.—July 3d, 1854. In Latitude 9 36 South, the Suns bearing by Compass at Rising wasE. 12° 42 N. Required the Variation. Answer.—The True Amplitude is E. 23* 22 N., and the Variation 10* 40 Westerly. Question 2d.—Sept. 2l8t, 1854. In Latitude 26 32North, the Suns bearing by Compass at Settincwas West 6° 15 South. Required the Variation. Answer.—The True AmpHtude is W. 1* 7
. A new treatise on the practice of navigation at sea : containing all the details necessary to enable the mariner to become a good practical navigator. . but this is seldom necessary at Sea. QUESTIONS FOR EXERCISE Question let.—July 3d, 1854. In Latitude 9 36 South, the Suns bearing by Compass at Rising wasE. 12° 42 N. Required the Variation. Answer.—The True Amplitude is E. 23* 22 N., and the Variation 10* 40 Westerly. Question 2d.—Sept. 2l8t, 1854. In Latitude 26 32North, the Suns bearing by Compass at Settincwas West 6° 15 South. Required the Variation. Answer.—The True AmpHtude is W. 1* 7 N., and the Variation 7* 22 Easterly. MA NAUTICAL ASTROPiuMY. FINDING THE VARIATION OF THE COMPASS FROM AN AZIMUTH. An Azimuth means an Angle at the Zenith, contained between the Meridian of the Observer and a Oirah*i Altitude passing through the body. DIAGRAMOf an Azimuth in 381° North Latitude. Fig. Ir this Figure the Suns True Altitude is 25, his Declination 17° South, and the Latitude 38 SO^Nortl ;•fil i will be perceived that the Co-Altitude, or the Suns distance from the Zenith, the Polar Distance,and the Co-Latitude are given, which form the three sides of an Oblique Spherical Triangle, to find theAngle of Azimuth at the Zenith, which is measured on the Horizon by a Circle of Altitude passing throughthe body, and cutting the Horizon at right angles. The Azimuth Angle in the above Figure is meas-ured from the North point of the Horizon, because the North Pole of the heavens is elevated, and it contains141° 46 : but for convenience sake its Supplement is generally used, that is, what it wants of 180°, andis reckoned from the opposite point of the Horizon, because the Sun is South of the observer in North Latitude, and North of the observer in South Latitude. RULE. Correct the Suns observed Altitude by Table IX. Correct the Suns Declination by Table XI, and find his PolarD
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