Nor was this important magnetic element known to Columbus when he sailed from the shores of the Old World in 1492 as appears from the surprise with which he noticed the deviation of the needle from North as well as from the consternation of his pilots. Columbus has the unquestionable merit of being the first to observe and record the change of declination with change of place. The first printed edition of the Epistola, now very rare, was prepared by Achilles Gasser, a physician of Lindau, a man well versed in mathematics, astronomy, history and philosophy. The work was printed in Augsburg in 1558. A copy of this early print is among the treasures of the Wheeler collection in the library of the American Institute of Electrical Engineers, New York. It was from this text that the translation which follows was made. Besides the Latin edition of Gasser, 1558, there is also that of Libri in his _Histoire des Sciences Mathématiques_, 1838; of Bertelli, 1868, and Hellmann, 1898. Bertelli’s is a learned and exhaustive work in which the Barnabite monk, sometimes called by mistake, Barnabita, instead of Bertelli, collates and compares the readings of the two Vatican codices with other texts, adding copious references and explanatory notes. It appeared in the _Bulletino di Bibliografia e di Storia delle Scienze Matematiche e Fisiche_ for 1868. Of translations, we have that which Richard Eden made from Taisnier’s pirated extracts, the first dated edition appearing in 1579. Cavallo’s _Treatise on Magnetism_, 1800, also contains some of the more remarkable passages. The only complete English translation that we have, appeared in 1902 from the scholarly pen of Prof. Silvanus P. Thompson, of London. It is an _édition de luxe_ beautifully rubricated, but limited to 250 copies. The translation was based on the texts of Gasser and Hellmann, amended by reference to a manuscript in the author’s possession, dated 1391. We are informed that Mr. Fleury P. Mottelay, of New York, the learned translator of Gilbert’s _De Magnete_, possesses a manuscript version by Prof. Peirce, of Harvard, of the Paris codex, of which he made a careful study in an endeavor to decipher the illegible parts. PART I THE LETTER OF PEREGRINUS PART I CHAPTER I PURPOSE OF THIS WORK Dearest of Friends: