Footnote 49
Part II, §23.  Here the altitude of a star (A) is to be taken twice; firstly, when it is on the meridian in the most southern point of its course, and secondly, when on the meridian in the most northern point, which would be the case twelve hours later.  The mean of these altitudes is the altitude of the pole, or the latitude of the place.  In the example given, the star A is only 4° from the pole, which shews that it is the Pole-star, then farther from the Pole than it is now.  The star F is, according to Chaucer, any convenient star having a right ascension differing from that of the Pole-star by 180°; though one having the same right ascension would serve as well.  If then, at the first observation, the altitude of A be 56, and at the second be 48, the altitude of the pole must be 52.  See fig. 13, Plate V.