corresponding to it, we have the date March 16 as nearly as we can determine it by observing the intricate divisions in the figure. The next passage "Noon hyer was he, whan she redy was" means evidently, 'he was no higher than this (i. e. four degrees) above the horizon when she was ready'; that is, it was a little past six. The method used in determining the time of day by observation of the sun's position is explained in the Astrolabe ii, 2 and 3. First the sun's altitude is found by means of the revolving rule at the back of the astrolabe. The rule, a piece of metal fitted with sights, is moved up and down until the rays of the sun shine directly through the sights. Then, by means of the degrees marked on the back of the astrolabe, the angle of elevation of the rule is determined, giving the altitude of the sun. The rest of the process involves the use of the _front_ of the astrolabe. This side of the circular plate, shown in Fig. 2, had a thick rim with a wide depression in the middle. On the rim were three concentric circles, the first showing the letters A to Z, representing the twenty-four hours of the day, and the two innermost circles giving the degrees of the four quadrants. The depressed central part of the front was marked with three circles, the 'Tropicus Cancri', the 'AEquinoctialis,' and the 'Tropicus Capricorni'; and with the cross-lines from North to South, and from East to West. There were besides several thin plates or discs of metal of such a size as exactly to drop into the depression spoken of. The principal one of these was the 'Rete' and is shown in Fig. 2. "It consisted of a circular ring marked with the zodiacal signs, subdivided into degrees, with narrow branching limbs both within and without this ring, having smaller branches or tongues terminating in points, each of which denoted the exact position of some well-known star. * * * The 'Rete' being thus, as it were, a skeleton plate, allows the 'Tropicus Cancri,' etc., marked upon the body of the instrument, to be partially seen below it. * * * But it was more usual to interpose between the 'Rete' and the body of the instrument (called the 'Mother') another thin plate or disc, such as that in Fig. 5, so that portions of this latter plate could be seen beneath the skeleton-form of the 'Rete' (i. 17). These plates were called by Chaucer 'tables', and sometimes an instrument was provided with several of them, differently marked, for use in places having different latitudes. The one in Fig. 5 is suitable for the latitude of Oxford (nearly). The upper part, above the Horizon Obliquus, is marked with circles of altitude (i. 18), crossed by incomplete arcs of azimuth tending to a common centre, the zenith (i. 19)." [Skeat, _Introduction to the Astrolabe_, pp. lxxiv-lxxv.]