TERRESTRIAL MAGNETISM. 57 



as well as of the Arabs, speak of rocky islands. which cause 

 disasters to mariners, either by drawing out, by virtue of 

 their natural magnetic power, all the iron which held the 

 wooden framework of the ship together, or by attracting 

 and immovably enchaining it. Under the influence of 

 such imaginations, the idea of the polar conjunction of all 

 the lines of declination had associated with it, in early times, 

 the more material image of a high magnetic mountain, in 

 near proximity to one of the poles of the earth. In the 

 remarkable map of the new continent, appended to the 

 Roman edition of 1508 of Ptolemy's Geography, we find 

 to the north of Greenland (Gruentlant), which is repre- 

 sented as belonging to the eastern part of Asia, the north 

 magnetic pole figured as a mountainous island rising 

 out of the sea. Its position was gradually removed farther 

 to the south in the " Breve Compendio de la Sphera" of 

 Martin Cortez, in 1545, as well as in Livio Sanuto's 

 "Geographia de Tolomeo," in 1588. Great expectations 

 were attached to reaching this point, which was termed " el 

 calamitico " and from some notion, which was very late 

 in disappearing, it was supposed that whoever should reach 

 the magnetic pole would find " alcun miraculoso stupendo 

 effetto." 



Until near the end of the 16th century, the magnetic 

 declination, which is the element exercising the most direct 

 influence on the requirements of navigation, was the only 

 one which received attention. Instead of the one " line of 

 no variation," found by Columbus in 1492, the learned 

 Jesuit Acosta, in 1589, thought, from the information which 

 he had gathered from Portuguese seamen, that he could state, 

 in his excellent work, " Historia natural de las Indias," the 



