An astrological calculation in the vernacular from the 12th century

Now in the British Library, MS Harley 5402 is a collection of astrological treatises from different sources. It consists of two groups of texts, with the first, penned by a 12th-century professional Italian scribe, covering folios 1r-69r, and the second, added in the 14th century, running from folio 70r to 104v. Acting as a watershed between the two parts, folio 69 contains three short texts added by non-professional hands in a deplorable Latin, strongly influenced by the vernacular (Italian and Occitan). - A fourth text, in a variety of Old Italian, was inserted by yet another non-professional hand, with all elements pointing to the city of Pisa in the second half of the 12(th) century: this conclusion is supported by the palaeographic analysis carried out in this article. The Old Italian text, La rasionedele littere Juliiinperator, discovered by professor Charles Burnett of the Warburg Institute in London, has resisted every attempt at interpretation until the present day: for instance, efforts to link this "method for calculating the letters of Emperor Julius" to the Julian calendar with its Dominical letters have proved fruitless. What is clear, however, is that we are looking at the oldest known specimen of Italian scientific prose.