The elements of navigation : containing the theory and practice, with all the necessary tables, to which is added, a treatise of marine fortification ... (1754)
Robertson, J. (John), 1712-1776, Adams, Charles Francis, 1807-1886, former owner. BRL, Adams, John, 1735-1826, former owner. BRL, Boston Public Library) John Adams Library BRL · London : Printed for J. Nourse ... · leaf 108
Therefore L. c, or Z.B=(half 120°; or=) 6o°=Z.A. Confequently cb = ab = ac.! From a, draw the radius ae perpendicular to cb.j Then ae bife&s the arc cb, and its chord. (207) And cd = fine of (the arc ce == half of 6o° =) 300. (298) Confequently cd is equal to half the radius ab. 319. Hence,… … 320. PROP. III.To find the fine of one minute of a degree* It is evident (261), that the lefs the arc is, the lefs is the difference be-tween the arc and its fine, or half chord ; fo that a very fmall arc, fuchas that of one minute, may be reckoned to differ from its fine, by fo fmalla quantity,…
Navigation · Nautical astronomy · Fortification
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