First among the instruments without which systematic ocean navigation would have been impossible, the magnetic compass had been introduced into southern Europe and was used by Biscayan and Catalan sailors before the end of the twelfth century.[372] Parties of Crusaders had learned the virtues of the suspended needle from the Arabs, who are said to have got their knowledge indirectly from China in the course of their eastern voyages.[373] It seems to have been at Amalfi that the needle was first enclosed in a box and connected with a graduated compass-card. Apparently it had not come into general use in the middle of the thirteenth century, for in 1258 the famous Brunetto Latini, afterwards tutor of Dante, made a visit to Roger Bacon, of which he gives a description in a letter to his friend the poet Guido Cavalcanti: "The Parliament being summoned to assemble at Oxford, I did not fail to see Friar Bacon as soon as I arrived, and (among other things) he showed me a black ugly stone called a magnet, which has the surprising property of drawing iron to it; and upon which, if a needle be rubbed, and afterwards fastened to a straw so that it shall swim upon water, the needle will instantly turn toward the Pole-star: therefore, be the night ever so dark, so that neither moon nor star be visible, yet shall the mariner be able, by the help of this needle, to steer his vessel aright. This discovery, which appears useful in so great a degree to all who travel by sea, must remain concealed until other times; because no master mariner dares to use it lest he should fall under the imputation of being a magician; nor would the sailors venture themselves out to sea under his command, if he took with him an instrument which carries so great an appearance of being constructed under the influence of some infernal spirit.[374] A time may arrive when these prejudices, which are of such great hindrance to researches into the secrets of nature, will be overcome; and it will be then that mankind shall reap the benefit of the labours of such learned men as Friar Bacon, and do justice to that industry and intelligence for which he and they now meet with no other return than obloquy and reproach."[375] [Footnote 372: Navarrete, _Discurso historico sobre los progresos del arte de navegar en Espana_, p. 28; see also Raymond Lully's treatise, _Libro felix, o Maravillas del mundo_ (A. D. 1286).]