TO THE READER.

He declared that he had been unable to publish it under the current circumstances; furthermore, he promised that he would ensure the long-desired codex would come into my hands as its future editor. Indeed, at the beginning of this year, I received Theon's Astronomy with a most grateful heart, and I dedicated to it all the time that other duties left me from the month of January until this very day.

I now know that this codex is the same one that had been in the library of Charles de Montchal, and that it is a most accurate—and therefore most flawed—transcript of the most flawed Milanese codex: a matter which will be demonstrated in its proper place. Therefore, it seemed to me that I could do without the Milanese codex without the greatest detriment to myself, the readers, and Theon himself. I also felt I could prudently exercise my judgment in correcting the author's text according to the standards of grammar and mathematics, by calling for assistance from both the Latin translation of the greater part of the work, which I found inserted into Chalcidius's Commentario in Timaeum Commentary on the Timaeus, and from Greek authors on the same science. Among these, since the manuscript work of George Pachymeres, De quatuor mathematicis disciplinis On the Four Mathematical Disciplines, remained unpublished in the Royal Library of Paris, I attentively read the astronomical book, which is the fourth part of the work, noting down what seemed useful and even transcribing some passages, which you will find in the first Appendix of this volume. In the second Appendix will appear—edited a bit more correctly from the excellent and rare edition of Fabricius, but now equipped for the first time with geometric diagrams that