viii CONTENTS. 



PAGE 



And other mediaeval poems referring to magnetic polarity 154 



The spurious treatise of Aristotle 157 



Mediaeval lodestoue myths and fables 159 



Roger Bacon and his discoveries 160 



Ancient conceptions of the universe 163 



CHAPTER VII. 



Peter Peregrinus 165 



His perpetual motion 167 



His marvelous magnetic discoveries 169 



His development of the Mariner's Compass 184 



Flavio Gioja and his Compass card 187 



Plagiarists of Peregrinus 191 



CHAPTER VIII. 



The revival of literature in Europe 193 



Henry the Navigator and Portuguese voyages 194 



Christopher Columbus and his magnetic discoveries 196 



Attempts to account for Compass variation by the Magnetic Rocks . 202 



The voyages of Vasco da Gama and Magellan 205 



Peregrinus' disclosure of the magnetic field of force 207 



Hartmann partly recognizes Dip of the Compass needle 209 



Norman's discovery and explanation of Dip 211 



Magnetic deceptions of the period 219 



Paracelsus and his magnetic nostrums 220 



CHAPTER IX. 



Fra Paolo (Pietro Sarpi) 224 



His treatises on the magnet . 225 



Cesare observes magnetism by earth's induction 227 



The Jesuits dispute Sarpi's discoveries 228 



John Baptista Porta 230 



His Society 231 



His relations to Sarpi 232 



His treatise on natural magic and the magnetic discoveries therein 



recorded 234 



And especially the magnetic field of force 235 



And telegraphic communication by magnets 239 



Jerome Fracastorio 241 



Jerome Cardan 243 



And his differentiation of magnetic and amber effects 249 



The physicians as physicists 255 



CHAPTER X. 



William Gilbert 258 



The object of his work 268 



