------------------------------------------------------------------------ [128] _Li Louvres dou Trésor_, Chabaille, Paris 1863. ------------------------------------------------------------------------ When speaking of the two principal movements of the skies, he quotes a curious old idea which had been mentioned by Isidore of Seville, that they are in contrary directions because the tremendous speed of the diurnal motion would shake the whole universe to pieces if it were not that the seven planets go as it were to meet it, and soften its vehemence:— “Li firmamenz court de orient en occident entre jor et nuit une fois, si roidement et si fort que sa pesanteur et so grandor la feroient tout tressaillir, se ne fussent les VII. planetes qui vont aussi comme a l’encontre dou firmament, et atemprent son cours selonc son erre.”[129] ------------------------------------------------------------------------ [129] _Ibid._ ------------------------------------------------------------------------ The _Acerba_ of Cecco d’Ascoli was another encyclopædic work, but in Italian verse. It was very much the fashion in those days to undertake a compilation of all kinds of knowledge, and this was doubtless very useful when few books could be owned by any single reader. Cecco had a considerable knowledge of natural science, and astrology was of great importance in his eyes. Though Dante never mentions him or his work, he can hardly have been ignorant of it, especially as he himself is mentioned in it. Nor does he mention Ristoro of Arezzo, yet we find many ideas and expressions in Dante’s writings which are also in the _Composizione del Mondo_. Even if he did not borrow from it, the book is worth study by anyone interested in the popular astronomy of the thirteenth century. We learn from the author that he wrote his book in Arezzo, finishing it in the year 1282, that is about thirty years before Dante’s _Convivio_ appeared. The opening words run:— “Incominiciasi il libro della Composizione del Mondo colle sue cagioni: composto da Ristoro di Arezzo in quella nobilissima città ... etc.”[130] ------------------------------------------------------------------------ [130] “Here beginneth the book of the _Composition of the World together with its Causes_: written by Ristoro of Arezzo in that most noble city.” ------------------------------------------------------------------------ and the closing words are:— “Compiuto e questo libro sotto li anni di Cristo nel mille dugento ottantadue. Ridolfo imperadore aletto. Martino quarto papa residente. Amen.”[131] ------------------------------------------------------------------------ [131] “Here endeth this book, in the year of our Lord one thousand two hundred and eighty-two. Rudolph Emperor at this date. Martin IV. resident Pope.” Amen. ------------------------------------------------------------------------