26 MEMOIR OF 



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

 tliey witnessed together one of the great eruptions 

 of Yesuvius. 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 18)8, 

 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 



