[10] The Alidada is the traversing index bar which carries the
    dioptra, pinnules, or sight-vanes.  The word is found in some older
    English Dictionaries, and in France and Italy is still applied to the
    traversing index of a plane table or of a sextant.  Littre derives it
    from (Ar.) ’adad, enumeration; but it is really from a quite
    different word, al-idadat [Arabic] “a door-post,” which is found in
    this sense in an Arabic treatise on the Astrolabe. (See Dozy and
    Engelmann, p. 140.)

[11] This is an error of Ricci’s, as Mr. Wylie observes, or of his
    reporter.

The Chinese divide their year into 24 portions of 15 days each.  Of these 24 divisions twelve called Kung mark the twelve places in which the sun and moon come into conjunction, and are thus in some degree analogous to our 12 signs of the Zodiac.  The names of these Kung are entirely different from those of our sign, though since the 17th century the Western Zodiac, with paraphrased names, has been introduced in some of their books.  But besides that, they divide the heavens into 28 stellar spaces.  The correspondence of this division to the Hindu system of the 28 Lunar Mansions, called Nakshatras, has given rise to much discussion.  The Chinese sieu or stellar spaces are excessively unequal, varying from 24 deg. in equatorial extent down to 24’. (Williams, op. cit.) [See P.  Hoang, supra p. 449.]

[12] Mr. Wylie is inclined to distrust the accuracy of this remark, as the
    only city nearly on the 36th parallel is P’ing-yang fu.

But we have noted in regard to this (Polo’s Pianfu, vol. ii. p. 17) that a college for the education of Mongol youth was instituted here, by the great minister Yeliu Chutsai, whose devotion to astronomy Mr. Wylie has noticed above.  In fact, two colleges were established by him, one at Yenking, i.e.  Peking, the other at P’ing-yang; and astronomy is specified as one of the studies to be pursued at these.  (See D’Ohsson, II. 71-72, quoting De Mailla.) It seems highly probable that the two sets of instruments were originally intended for these two institutions, and that one set was carried to Nanking, when the Ming set their capital there in 1368.

[13] The 28 sieu or stellar spaces, above spoken of, do not extend to
    the Pole; they are indeed very unequal in extent on the meridian as
    well as on the equator.  And the area in the northern sky not embraced
    in them is divided into three large spaces called Yuen or
    enclosures, of which the field of circumpolar stars (or circle of
    perpetual apparition) forms one which is called Tze-Wei.
    (Williams.)

    The southern circumpolar stars form a fourth space, beyond the 28
    sieu.  Ibid.