The diurnal movement of the starry heaven is also alluded to in the _Convivio_, and contrasted with that immensely slow movement which was discovered by Hipparchus, and is called by us Precession. The starry heaven, says Dante, displays one of its poles to us, and keeps the other hidden; and in like manner it displays only one movement to us, and keeps the other almost hidden. By the first, it revolves once in every day from east to west; the other is nearly insensible, being only one degree in a hundred years, and it is from west to east.[268] This is the value of precession as given by Alfraganus, following Ptolemy. ------------------------------------------------------------------------ [268] _Conv._ II. xv. 10-14, and 96-104. ------------------------------------------------------------------------ It was this stupendous and mysterious cycle which was used by Dante to measure the age of Beatrice, though for his own he used (as we saw) the ordinary measure of the sun’s period. When he first saw “la gloriosa donna”[269] she had only been in this life so long that the starry heaven had moved towards the east one-twelfth part of a degree. Therefore, she was one-twelfth of a hundred years old, or 8 years 4 months, “so that it was near the beginning of her ninth year that she appeared to me, and I saw her nearly at the end of my ninth.”[270] ------------------------------------------------------------------------ [269] “The glorious Lady.” [270] _V. N._ ii. 9-15. ------------------------------------------------------------------------ Dante tells us how many stars had been counted by “the sages of Egypt,” by whom he means Ptolemy and the other Alexandrians: he did not know that the star catalogue of the _Almagest_ was originally made by Hipparchus of Rhodes. “Dico ch’ il cielo stellato ci mostra molto stelle; chè, secondochè li savi d’Egitto hanno veduto, infino all’ultima stella che appare loro in meridie, mille ventidue corpora di stelle pongono, di cui io parlo.”[271] ------------------------------------------------------------------------ [271] “I say that the starry heaven displays a multitude of stars to us, for as the Sages of Egypt have perceived, including the last star which appears to them in the south, they reckon one thousand and twenty-two starry bodies, of which I am now speaking.” _Conv._ II. xv. 18-22. (_Jackson_). ------------------------------------------------------------------------ It will be noted that he carefully avoids saying that this is the number of all the stars visible from the whole earth. Had he, like Ristoro, run away with the idea that a blank space on the globe meant a blank in the sky, his night sky seen from Purgatory would have been strangely bare and dull! Yet both writers used the same text-book. Dante is here following Alfraganus closely, for he had written in his nineteenth chapter:—