MAGNETIC VARIATION. 123 



Europeans could not have learned, from their own expe- 

 rience, the direction of the magnetic needle in the southern 

 hemisphere before the second half of the 15th century, when 

 they may have obtained an imperfect knowledge of ijt from 

 the adventurous expeditions of Diego Cam with Martin Be- 

 haim, and Bartholomew Diaz, and Vasco de Gama. The 

 Chinese, who, as early as the 3d century of our era, as well 

 as the inhabitants of Corea and the Japanese Islands, had 

 guided their course by the compass at sea, no less than by 

 land, are said, according to the testimony of their earliest 

 writers, to have ascribed great importance to the south di- 

 rection of the magnetic needle, and this was probably main- 

 ly dependent on the circumstance that their navigation was 

 entirely directed to the soutli and southwest. During these 

 southern voyages, it had not escaped their notice that the 

 magnetic needle, according to whose direction they steered 

 their course, did not point accurately to the south pole. We 

 even know, from one of their determinations, the amount* 

 of the variation toward the southeast, which prevailed dur- 

 ing the 12th century. The application and farther diffusion 

 of such nautical aids favored the very ancient intercourse of 

 the Chinese and Indians with Java, and to a still greater 

 extent the voyages of the Malay races and their colonization 

 of the island of Madagascar.! 



Although, judging from the present very northern position 

 of the magnetic equator, it is probable that the town of 

 Louvo, in Siam, was very near the extremity of the northern 

 magnetic hemisphere, when the missionary father, Guy Ta- 

 chard, first observed the horary alterations of the magnetic 

 variation at that place in the year 1682, it must be remem- 

 bered that accurate observations of the horary declination in 

 the southern magnetic hemisphere were not made for fully a 

 century later. John Macdonald watched the course of the 



ularity in the turning hours. Every where in nature, where various 

 causes of disturbances act upon a phenomenon of motion at recurring 

 periods (whose duration, however, is still unknown to us), the law by 

 which these disturbances are brought about often remains for a long 

 time unexplained, in consequence of the perturbing causes either re- 

 ciprocally neutralizing or intensifying one another. 



* See my Examen Grit, de FHist. de la Geogr., t. m., p. 34-3 /. 

 The most ancient notice of the variation given by Keutsungchy, a 

 writer belonging to the beginning of the 12th century, was east f 

 south. Klaproth's Lettre sur Vinvention de la Boussole, p. 68. 



t On the ancient intercourse of the Chinese with Java, accordii 

 statements of Fahian in the Fo-kue-si, see Wilhelm von Humboldt, 

 Ueber die Kaivi Sprache, bd. i., s. 16. 



