SECTION XIX. 275 cent in Portugal, to Cat Island among the Bahama Islands is west and by south. If no rhumb line passes through those places; then that rhumb line to which those two places lie most parallel, shews their bearing: Thus the course from Barbadoes to Cape Finisterre is orth -east and by east, or thereabouts. If the learner lias a mind to see the reason, why there must be such a difference be- twixt the angle of position between two places, and their course of bearing to each other, I know not how to represent it upon a Hat surface plainer than by figure xxi. Suppose the four cardinal points, north, south, east, and west, are representedon the globe by the letters N. S. W. E: Suppose three distant places are B Barbadoes, C Cape Finis- terre, and A Azoff. If the surface of the earth were not sphe- rical, but a plane, and the meridians of these places were all parallel (as in that representation or projection of the globe, which is called Mercator's chart) then their angle of positionand their courseof bearing would be the same : Then as N s is the meridian of the place B, so q u would be the meridian of the place c, viz. a strait line andparallel to N s : Then the line B c A would be the line or rhumb of north-east, viz. 45 degrees distant from N s ; which would represent both the angle of position and the course of bearing between all the three pla- ces B C and A : For the angle q c A would be the same with the angle N B A ; and thus A would still bear north-east from c and from s.* But the earth being of a spherical figure and the meridians meeting in the poles, the meridian of B on the globe being brought to the zenith is N s ; the meridian of c is the curve line N c m ; and the meridian of A is the curve line N' A z ; all which meet in N the north -pole. ' Now though the strait line B c A shews the angle of position between the three places B c and A, (as B stands on the globe at the zenith) yet the line B c a does by no means make the same angles, or has the same bearing with the curve line N c en (which is the meridian of c) as it does with N s (which is the meridian of B :) and it still makes more different angles with the curve line N A z (which is the meridian of A.) Thence it follows, that all the rhumb lines must be a sort of spi- ral lines on the globe, except the north and south, which is the meridian, and the equator with its parallels of east and west, which are circles,t * And for this reason in those sea chartswhere the points of the compass or rhumbs are drawn in strait lines quite through the chart, the meridian or lines of longitude are all made straitand parallel linea: For if the meridians were a little curved as they are commonly in maps, the rhumba could not be drawn through the chart in strait lines. See Sect. Xi. OfSea Charta. All the other lines of east and west besides the equator, are parallels of latitude, andare lesser circles. And though the line of east and west in tbi} e2
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