American practical navigator: an epitome of navigation and nautical astronomy (1914)
Bowditch, Nathaniel, 1773-1838, Logan, George Wood, 1868-1915, United States. Navy Dept. Bureau of Equipment · Washington, Govt. Print. Off · leaf 159
it be obtainedfrom observations of celestial bodies or from bearings or distances of terrestrialobjects. 366. Since the direction of a circle at any point—that is, the direction of thetangent—must be perpendicular to the radius at that point, it follows that theSumner line always lies in a… … perpendicular to the bearings of the bodiesOA and OA. This fact has a most im- FlG. 55. portant application in the employment ofthe Sumner line. 367. USES OF THE SUMNER LINE.—The Sumner line is valuable because itgives to the navigator a knowledge of allof the probable positions of his vessel,while…
Navigation · Nautical astronomy
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