TO THE READER.

hardly seemed to be confirmed as existing in the Ambrosian Library until the time of Bernard de Montfaucon. For he provides only one mention of a codex marked with the name of Theon of Smyrna, taken from the library's catalog, which is highly suspicious: Theon of Smyrna, or rather an anonymous work, on the sphere and on Plato.

As far as the Toulousian codex is concerned, one finds in Labbe, in the catalog of the manuscript codices of Charles de Montchal, Archbishop of Toulouse, this title: "Theon of Smyrna's On Those Things Useful for Mathematics, On the figure of the heavens and the earth from the motion of the stars. It begins: 'That the whole cosmos.' It ends: 'moving the least amount.'" But regarding this precious codex, which Bullialdus had also seen, I was unaware until a few months ago what had subsequently become of it.

Nor did I know any better that a copy of that Parisian codex existed at Leiden; once read, the very learned de Gelder rightfully declared that work of Theon more useful than the work of Cleomedes for explaining the history of astronomy, and noted that it contains, besides many documents about the greatest men among the ancients in mathematical science, the entire verses of the poets Alexander, Ibycus, and Aratus