These rather tremendous texts may make one fear that the "three godless painters" had found little pity in their master; but most sincere Christians are better than their creeds, and more charitable than the old-world imprecations, admonitions, and denunciations, with which they soothe their Cerberus of an old Adam, who is not allowed to use his teeth to the full extent that their formidable nature would seem to warrant. For have they not been told above all things to love their enemies, and do good to those whom they would naturally hate, by a master whom they really love and strive to imitate? IV Dürer's last years were given more and more to writing down his ideas for the sake of those who, coming after him, would, he was persuaded, go on far before him in the race for perfection. In 1525 he published his first book--"Instruction in the Measurement with the Compass, and Rules of Lines, Surfaces, and Solid Bodies, drawn up by Albert Dürer, and printed, for the use of all lovers of art, with appropriate diagrams." It contains a course of applied geometry in connection with Euclid's Elements. Dürer states from the very commencement that "his book will be of no use to any one who understands the geometry of the 'very acute' Euclid; for it has been written only for the young, and for those who have had no one to instruct them accurately." Thausing tells us his work shows certain resemblances to that of Luca Pacioli, a companion of Leonardo's, who may have been the "man who is willing to teach me the secrets of the art of perspective," and whom Dürer in 1506 travelled from Venice to Bologna to see; it is even possible that he saw Leonardo himself in the latter town. In 1527 he issued an essay on the "Art of Fortification," which the development of artillery was then transforming; and authorities on this very special science tell us that Dürer is the true author of the ideas on which the "new Prussian system" was founded. It was dread of the unchristian Turk who was then besieging Vienna which called forth from Dürer this excursion. He dedicated it in the following terms: To the most illustrious, mighty prince and lord, Lord Ferdinand, King of Hungary and Bohemia, Infant of Spain, Archduke of Austria, Duke of Burgundy and Brabant, Count of Hapsburg, Flanders, and Tirol, his Roman Imperial Majesty, our most gracious Lord, Regent in the Holy Empire, my most gracious Sire.