Today | News | Books | Recipes Adventure | Science Fiction | Ghost stories | Poetry | Children | History Books. They are called _arcus horarum inequalium_, as they shew the 'houres inequales.' 21. In fig. 2, Pl. II, the _Rete_ is shewn as it appears when dropped into the depression in the front of the instrument. The shape of it varied much, and another drawing of one (copied from Camb. Univ. MS. Ii. 3. 3, fol. 66 _b_) is given in fig. 9, Pl. IV. The positions of the stars are marked by the extreme points of the metal tongues. Fig. 2 is taken from the figures in the Cambridge MSS., but the positions of the stars have been corrected by the list of latitudes and longitudes given by Stöffler, whom I have followed, not because he is _correct_, but because he probably represents their positions as they were supposed to be in Chaucer's time very nearly indeed. There was not room to inscribe the names of all the stars on the _Rete_, and to have written them _on the plate below_ would have conveyed a false impression. A list of the stars marked in fig. 2 is given in the note to § 21, l. 4. The Ecliptic is the circle which crosses the Equinoctial at its East and West points (fig. 2). In Chaucer's description of the zodiac, carefully note the distinction between the Zodiac of the Astrolabe and the Zodiac of Heaven. The former is only _six_ degrees broad, and shews only the northern half of the heavenly zodiac, the breadth of which is _imagined_ to be 12 degrees. Chaucer's zodiac only shewed _every other_ degree in the divisions round its border. This border is divided by help of a table of right ascensions of the various degrees of the ecliptic, which is by no means easily done. See Note on l. 4 of this section. I may add that the _Rete_ is also called _Aranea_ or _Volvellum_; in Arabic, _Al´ancab[=u]t_ (the spider). 22. _The Label._ See fig. 6, Pl. III. The _label_ is more usually used on the _front_ of the instrument, where the _Rete_ and other plates revolve. The _rule_ is used on the _back_, for taking altitudes by help of the scale. 23. _The Almury_; called also _denticulus_, _ostensor_, or 'calculer.' In fig. 2, it may be seen that the edge of the _Rete_ is cut away near the head of Capricorn, leaving only a small pointed projecting tongue, which is the almury or denticle, or (as we should now say) pointer. As the _Rete_ revolves, it points to the different degrees of the border. See also fig. 9, where the almury is plainly marked. Part II, § 1. [The Latin headings to the propositions are taken from the MS. in St. John's College, Cambridge.] See fig. 1. Any straight edge laid across from the centre will shew this at once. Chaucer, reckoning by the old style, differs from us by about eight days. The first degree of Aries, which in his time answered to the 12th of March, now vibrates between the 20th and 21st of that month. This difference of eight days must be carefully borne in mind in calculating Chaucer's dates. 2. Here 'thy left side' means the left side of thine own body, and therefore the right or Eastern edge of the Astrolabe. In taking the altitude of the sun, the rays are allowed to shine through the holes; but the stars are observed by looking through them. See figs. 1 and 3. 3. Drop the disc (fig. 5) within the border of the mother, and the _Rete_ over it. Take the sun's altitude by § 2, and let it be 25½°. As the altitude was taken by the _back_ of the Astrolabe, turn it over, and then let the _Rete_ revolve westward till the 1st point of Aries is just within the altitude-circle marked 25, allowing for the ½ degree by guess. This will bring the denticle near the letter C, and the first point of Aries near X, which means 9 A.M. At the same time, the 20th degree of Gemini will be on the _horizon obliquus_. See fig. 11, Pl. V. This result can be approximately verified by a common globe thus; elevate the pole nearly 52°; turn the small brass hour-circle so that the figure XII lies on the equinoctial colure; then turn the globe till IX lies under the brass meridian. In the next example, by the Astrolabe, let the height of Alhabor (Sirius) be about 18°. Turn the denticle Eastward till it touches the 58th degree near the letter O, and it will be found that Alhabor is about 18° high among the _almicanteras_, whilst the first point of Aries points to 32° near the letter H, i.e. to 8 minutes past 8 P.M.; whilst at the same time, the 23rd degree of Libra is almost on the _Horizon obliquus_ on the Eastern side. By the globe, at about 8 minutes past 8 P.M., the altitude of Sirius is very nearly 18°, and the 23rd of Libra is very near the Eastern horizon. See fig. 12, Pl. V. 4. The ascendent at any given moment is that degree of the zodiac which is then seen upon the Eastern horizon. Chaucer says that astrologers reckoned in also 5 degrees _of the zodiac_ above, and 25 below; the object being to extend the planet's influence over a whole 'house,' which is a space of the same length as a _sign_, viz. 30°. See § 36 below. 5. This merely amounts to taking the mean between two results. 6. This depends upon the refraction of light by the atmosphere, owing to which light from the sun reaches us whilst he is still 18° below the horizon. The nadir of the sun being 18° high on the W. side, the sun itself is 18° below the Eastern horizon, giving the time of dawn; and if the nadir be 18° high on the E. side, we get the time of the end of the evening twilight. Thus, at the vernal equinox, the sun is 18° high soon after 8 A.M. (roughly speaking), and hence the evening twilight ends soon after 8 P.M., 12 hours later, sunset being at 6 P.M. 7. Ex. The sun being in the first point of Cancer on the longest day, its rising will be shewn by the point in fig. 5 where the _horizon obliquus_ and _Tropicus Cancri_ intersect; this corresponds to a point between P and Q in fig. 2, or to about a quarter to 4 A.M. So too the sunset is at about a quarter past 8, and the length of the day 16½ hours; hence also, the length of the night is about 7½ hours, neglecting twilight. 8. On the same day, the number of degrees in the whole day is about 247½, that being the number through which the _Rete_ is turned in the example to § 7. Divide by 15, and we have 16½ equal hours. 9. The 'day vulgar' is the length of the 'artificial day,' with the length of the twilight, both at morn and at eve, added to it. 10. If, as in § 7, the day be 16½ hours long, the length of each 'hour inequal' is 1 h. 22½ m.; and the length of each 'hour inequal' of the night is the 12th part of 7½ hours, or 37½ m.; and 1 h. 22½ m., added to 37½ m., will of course make up 2 hours, or 30°. 11. This merely repeats that 15° of the border answer to an hour of the clock. The '4 partie of this tretis' was never written. 12. This 'hour of the planet' is a mere astrological supposition, involving no point of astronomy. Each hour is an 'hour inequal,' or the 12th part of the artificial day or night. The assumptions are so made that _first_ hour of every day may resemble the _name of the day_; the first hour |