54 ESSEX WORTHIES. 



down from Plutarch and Ptolemy that garlic rubbed over a magnet 

 destroys its power, unless, according to Ruelius, it be restored by 

 anointing it with goat's blood. Another fable of Marbodeus, that a 

 magnet is powerless in the presence of a diamond, is also refuted by 

 Porta. The latest work on magnetism, prior to the appearance of 

 (Gilbert's treatise, was a small pamphlet which appeared in 1597, 

 entitled " The Seaman's Supply," byWilliam Barlowe, which gave for 

 the use of navigators many facts about the declination of the com- 

 pass at different sea-ports, and about the amount of the dip at 

 different parts of the earth. 



All these earlier publications in magnetic subjects consisted, as 

 will be noticed in the announcement of isolated facts and properties 

 rather than in any systematic investigation or consistent explanation. 

 The significance of the facts was not seen ; and they were in many 

 cases mixed up with exaggeration and myth. The only explanations 

 or hypotheses which had been advanced as to the cause of the ten- 

 dency of the magnet or magnetised needle to point geographically 

 north and south were wild in the extreme. Gilbert himself enumer- 

 ates sundry of them in order to show how empty and ridiculous they 

 were. Serapio Mauritanus and others reported that in the Indies 

 there were magnetic mountains which would attract the ships as they 

 sail l)y and pull the iron nails out of them. Paracelsus and Cardan 

 considered that the magnet was governed by some virtue proceeding 

 from the constellation of the Great Bear ; and after the discovery that 

 the magnet did not point truly northward, Cardan suggested that the 

 star in the tip of the tail of the Great Bear was itself a magnet. 

 Bessard declared that the compass pointed not toward the pole of the 

 earth, but to the pole of the zodiac. Glaus Magnus and after him 

 Maurolycus declared that there was a magnetic island or loadstone 

 rock in the north sea toward which the compass turned its point. 

 Plancius even showed its position upon a chart of the globe. 



Such was the state of the science when " De Magnete " appeared. 

 The full title of the book, as it appears on the frontispiece of the 

 folio edition of 1600 is : Guilielmi Gilberti Cokestrensis, media 

 Londmensis, de magnete, magneticisqiie corporilms, et de magna jnagnete 

 iellure ; Physiologia ?iova, plurimis et argume7itis, et expert mentis 

 demonstrata. Londini. Excudebat Fetrus Short. Anno M.D.C. 



The volume opens with a glossary of terms and a table of con- 

 tents. The work is divided into six books, each book being sub- 

 divided into numerous short chapters. 



