[17]. assensiouns in the righte cercle. This exactly answers to our modern 'right ascension.' We hence obtain the true origin of the phrase. 'Right ascension' was, originally, the ascension of stars at places situate on the equator, and was most conveniently measured along the equatorial circle, by observation of the times of transit of the various stars across the meridian. In other latitudes, the ascension of every degree of the zodiac could be easily tabulated by observing what degree of the equator came to the meridian with the said degree of the zodiac; see l. 20. It hence appears that, whilst persisting in using 'longitudes' and reckoning along the zodiac, the ancients were obliged, in practice, to refer the degrees of longitude to the equator. The modern method of recognizing this necessity, and registering right ascensions as of more importance than longitudes, is a great improvement. The ancients were restrained from it by their unnecessary reverence for the zodiac. Cf. Ptolemy's Almagest, lib. i. c. xiii.
§ 29. Chaucer omits to say that the experiment should be made when the sun is very nearly on the meridian. Otherwise, the confusion of the azimuth with the hour-angle might cause a considerable error.
§ 30. [3]. That the phrase 'wey of the sonne' really means the sun's apparent diurnal course in this conclusion, may be further seen by consulting the Latin of Messahala. Cf. the Critical Note on p. [236].
§ 31. In my footnote, I have used the expression 'it does not mean, as it should, the zenith point.' I mean—'as, according to our modern ideas, it should';—for the derivation of zenith shews that the meaning used in this proposition is the older meaning of the two. See note above to i. 19. 7 (p. [357]).
[6]. 24 parties. These 24 parts were suggested by the 24 hours of the day. The '32 parts' used by 'shipmen' are due to the continual halving of angles. Thus, the four cardinal points have points half-way between them, making eight points; between which, we can insert eight more, making sixteen; and between these, sixteen more, making thirty-two. Hence the 32 points of the compass.
§ 33. [5]. We should probably insert or south after the word north. Such an insertion is authorised by MSS. B. and C.
§ 34. [3]. That 'upon the mones syde' means nearly in the same azimuth as the moon, is apparent from l. 11 below, where Chaucer says that some treatises make no exception even if the star is not quite in the same azimuth. This was certainly a rough mode of observation.
§ 35. [9]. right side, East side. See i. 6. 1 (p. 179).
[18]. episicle, epicycle. To account for the planetary motions, epicycles were invented. The moon, for instance, was supposed to revolve round a moving centre, which centre itself moved round the earth in a perfect circle. This came a little nearer to the true motion in some instances, but was hopelessly wrong, and nothing could be made of it, even when a second epicycle, revolving about a centre which moved in the first epicycle, was superadded. All that Chaucer says here is, that, whilst the centre of the moon's epicycle had a direct motion, the moon's motion in the epicycle itself was a reverse one, unlike that of the other planetary bodies. The subject is hardly worth further discussion, so I merely refer the reader to the Almagest, lib. iv. c. 5; and lib. ix. c. 5.
§ [36]. The 'equations of houses' means the dividing of the sphere into equal portions, and the right numbering of those portions or houses. The most important house was the first, or ascendent, just rising; the next in importance was the tenth, which was just coming on the meridian; then come the seventh or descendent, just about to set, and the fourth, just coming to the line of midnight. The next in importance were the succedents, or houses immediately following these, viz. the second, the eleventh, the eighth, and the fifth. The least important were the third, twelfth, ninth, and sixth. See [Fig. 14].