26 MEMOIR OF 



the same roof, in France, Germany, and Italy ; and 

 they witnessed together one of the great eruptions 

 of Vesuvius. They made numerous magnetic ex- 

 periments, and verified Biot's theory respecting the 

 position of the magnetic equator. They also found 

 that the great mountain- chains, and even the active 

 volcanoes, have no appreciable influence on the 

 magnetic power; and they established the fact, 

 that it gradually diminishes as we recede from the 

 equator. 



In October 1818 Baron Humboldt visited Lon- 

 don, where he was received with merited distinc- 

 tion, and where it was said that the allied powers 

 had requested him to draw up a political view of 

 the South American colonies. 



He long enjoyed the favour and friendship of his 

 enlightened sovereign, Frederick -William III., the 

 late King of Prussia, who, in November 1818, 

 granted him an annual pension of 12,000 dollars 

 (upwards of 1700 sterling), with the view of 

 facilitating the execution of a plan which he had 

 formed of visiting India and Thibet. That plan he 

 was unfortunately unable to carry into effect, but 

 the pension has since been continued, in considera- 

 tion of his performing the duties of chamberlain at 

 the Prussian court. 



In 1822 he accompanied the king to the Con- 

 gress of Verona ; and he afterwards visited Venice, 

 Rome, and Naples. 



In 1827 and 1828 Humboldt delivered, at Ber- 

 lin, a course of lectures on the physical constitution 



