MEXICO AND THE UNITED STATES. 331 



rising to the height of more than 1,500 feet, formed in the 

 course of a night, during the year 1759. 



Humboldt and his companions descended to a depth of 250 

 feet into the crater, whence smoke was issuing from more than 

 2,000 small orifices. With considerable danger, on account of 

 the brittle nature of the blocks of lava, they reached almost to 

 the bottom of the crater, and there made an analysis of the air, 

 which was heavily laden with carbonic acid. The inhabitants 

 of that locality maintained that the heat of the crater had 

 formerly been much greater, and Humboldt gave it as his 

 opinion that the whole of the surrounding district is under- 

 mined by volcanic action. 



Humboldt returned to Mexico, across the Plateau of Toluca, 

 and ascended the volcano of that name on September 29. At 

 the capital he again made a sojourn of several months, for the 

 purpose of arranging his botanical and geological collections, 

 and of reducing his barometric and trigonometric observations, 

 while, at the same time, he laboured for the completion of his 

 tables of statistics, and carefully prepared materials for a map 

 of the country. 



During his first visit to the capital, Humboldt wrote to 

 Willdenow the following letter, dated April 29, 1803: 



6 1 received your welcome letter of the 1st October, 1802, a 

 few days after my arrival in, this great and imposing capital of 

 New Spain. My joy in reading it was all the greater from its 

 being the first and only letter I have received from you since 

 I left Europe, although I am convinced you must have written 

 to me frequently. Even from my brother I have received only 

 some five or six letters at most, during the four years that have 

 elapsed since I left Corunna. It seems as if an unfriendly 

 star had presided over our letters, if not over the ships that 

 carried them. But I will not complain, since I have now the 

 prospect of so soon embracing you all again. 



c We have already despatched to Europe some ten or twelve 

 consignments of newly gathered seeds ; one parcel went to the 

 Botanic Gardens at Madrid, among which, as I learn from the 

 " Annales de Historia Natural," Cavanilles has already dis- 

 covered some new species; a second parcel was enclosed to 

 the Jardin des Plantes at Paris ; and a third went by way of 



