112 



MAGNETISM. 



natural magnet (an oxide of iron) the name Magnes (n ayvns) ; derived, as is 

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

 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 

 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 

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

 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 

 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. 

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

 the year 1181. 



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

 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 

 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, 

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

 early in the twelfth century. 



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 

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

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

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



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

 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 

 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 

 volume of MS. tracts in the University of Ley den, a letter dated 1269, by Peter 

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

 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. 

 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 

 diminished. 



* See Kircher, De Magnete." 



