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.of Jupiter ’s apparent orbit, taken from Cassini’s drawing,and somewhat reduced in size.
In the above diagram a, b, c, etc., represent successive posi-tions of the point r, or centre of the epicycle (see Fig . XXX.);a, b, c, etc., corresponding positions of the planet, which are of.course always at the same distance (viz., the radius of the.epicycle) from the moving point p. By actually marking off-the points a, b, etc., and drawing a curve through them, it may.easily be seen how the peculiar looped form of the apparent
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•Fig . -XXXI. Showing that Jupiter occupies somewhat more than a year in describingone complete loop of its apparent orbit.
,orbit arises. The fact, however, to which we at present wishto draw attention is—that, when the centre of the epicycle hasreached h, so that its radius h h is parallel to a a, the planetwould have been once completely round it, and the time thus.occupied, according to our previous statement, would be equal.to one year; but it is clear that it would be necessary for the.centre of the epicycle to move on to k, and the planet to k,ibefore the radius jvould once more point to the Earth , and an
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