112 



MAGNETISM. 



natural magnet (an oxide of iron) the name Magnes (payvvs) • derived, as is > 

 supposed, from Magnesia, a district of Lydia, in which the natural magnet was c 

 found in greatest abundance. It was also called Lapis Heracleus, from He- > 

 raclea, a city of Lydia. From some passages in ancient authors, it would ( 

 seem that the force of magnetic attraction in very high degrees of intensity was ) 

 then generally known. Pliny relates that Dinochares proposed to Ptolemy < 

 Philadelphus to erect a temple at Alexandria, the dome of which should be ) 

 built of loadstone, so as to sustain in the air an iron statue of Arsinoe. Saint ( 

 Augustine also alludes to a statue thus suspended in the air in the middle of S 

 the temple of Serapis, at Alexandria. ( 



The polarity and directive powers of the magnet were discoveries of a much > 

 more recent date. The application of the magnetic needle to navigation must I 

 have immediately succeeded the first knowledge of its directive power, but the 5 

 discoverer is unknown ; and even the century which was honored by the in- ( 

 vention of this most beautiful application of science to the uses of man is un- > 

 certain. It is stated, in the account of the Chinese empire by Du Halde, that { 

 the directive power of the magnet was used in that part of the globe, for the / 

 purpose of land-journeys, more than a thousand years before the birth of Christ. ( 

 If such were the case, it is difficult to imagine that its use for sea-voyages ) 

 should have failed to spread itself westward until two thousand years later. \ 

 But, besides this, there are other reasons why little credit is to be given to the ; 

 accounts which ascribe this invention to the Chinese.* ( 



The earliest work in which the use of the mariner's compass is distinctly 5 

 mentioned is a manuscript poem of the twelfth century, preserved in the Royal < 

 Library at Paris, the authorship of which is attributed to Guiot de Provins. 5 

 Guiot was at the court of the emperor Frederick Barbarossa, held at Mentz in s 

 the year 1181. I 



Hansteen, in his work on the " Magnetism of the Earth," quotes an Icelandic s 

 historian, to show that the directive power of the loadstone was known a cen- ) 

 tury antecedent to the date of this poem. That annalist, relating a voyage J 

 made in those seas, says incidentally, that " in those times, seamen had no ) 

 loadstone in the northern countries." It appears that this writer, Arc Frode, J 

 was born about the year 1068, and therefore probably published his account i 

 early in the twelfth century. J 



Cardinal Jacques de Vitri, who lived about the year 1200, speaks of the ) 

 magnetic needle, in his " History of Jerusalem," as indispensable to those who J 

 make sea-voyages. It has also been said that it was first brought to Europe, 5 

 from the East, by Marco Polo. It is, however, certain that Vasco de Gama, J 

 the Portuguese navigator, used the compass in his voyage to India in 1497. 5 



Before it became the subject of accurate investigation, it was supposed that J 

 the direction of the compass was identical with that of the terrestrial meridian, ) 

 and that it pointed due north and south. The discovery of its variation, and S 

 that the amount and direction of the variation are different in different places, / 

 is generally ascribed to Columbus in 1492. There appears, however, in a s 

 volume of MS. tracts in the University of Leyden, a letter dated 1269, by Peter ) 

 Alsiger, in which the principal properties of the magnet are mentioned ; and, S 

 among others, the variation. The honor of this discovery has also been ascribed ) 

 to Grignon, a pilot of Dieppe, Sebastian Cabot, Gonzales, and others. 



Accurate observations of the variation of the needle began to be made at ) 

 Paris about the year 1550. At this time the variation was toward the east. S 

 It diminished in quantity, and became nothing in 1663 ; after which it passed } 

 to the west, increasing gradually till it attained a certain limit, after which it S 

 diminished. < 



* See Kircher, " De Magnete." 



