SECT, xxx.] THE MARINEK'S COMPASS. 347 



of the globe, from causes unknown, though Baron Hum- 

 boldt ascribes them to a reaction propagated from the 

 interior of the globe to the surface, analogous to the sudden 

 changes of electric tension in a thunder storm. In 1818 a 

 magnetic storm was synchronous from Paris to Kasan, 

 through forty-seven degrees of longitude; and one of the 

 greatest, which happened on the 28th of September, 1841, 

 was observed simultaneously at the magnetic observatories 

 at Toronto in North America, at the Cape of Good Hope, 

 at Prague in Europe, at Macao in China, and it was thought 

 to extend to Van Piemen's Land. Similar storms have been 

 observed simultaneously at Upsala in Sweden, and in Sicily. 

 Others of less extent and shorter duration occur more fre- 

 quently, and are, equally with the greater, not amenable to 

 any known laws. 



The aurora powerfully agitates the magnet, even when 

 invisible at the place of observation. 



The inventor of the mariner's compass, like most of the 

 early benefactors of mankind, is unknown. It is even 

 doubted which nation first made use of magnetic polarity 

 to determine positions on the surface of the globe. But it 

 is said that a rude form of the compass was invented in 

 Upper Asia, and conveyed thence by the Tartars to China, 

 where the Jesuit missionaries found traces of this instru- 

 ment having been employed, as a guide to land travellers, 

 in very remote antiquity. From that the compass spread 

 over the East, and was imported into Europe by the 

 Crusaders, and its construction improved by an artist of 

 Amalfi, on the coast of Calabria. It seems that the Chinese 

 only employed twenty-four cardinal divisions, which the 

 Germans increased to thirty-two, and gave the points the 

 names which they still bear. 



The variation of the compass was unknown until Columbus, 

 during his first voyage, observed that the needle declined 

 from the meridian as he advanced across the Atlantic. The 



