In 1829 Humboldt again became a traveler, the emperor Nicholas then sending out a well-appointed expedition to the n. of Asia, to explore the Ural and Altai mountains, the Chinese Dsongarei, and the Caspian sea. In this expedition Humboldt was accom panied by his two friends, Ehrenberg and Gustavus Rose. Its principal results were the scientific examination of the beds which produce gold and plating, the discovery of dia monds in an extra-tropical region, the astronomical determination of positions, magnetic observations, and geological and botanical collections. The whole journey occupied nine months, and extended to 2,320 miles. It is described in Rose's Mineralogical and Geo logical Travels to the Ural, the Altai, and the Caspian Sea (Mineralogisch-geognuaischer Reiss, etc., 2 vols., Berlin, 1837-42); and in Humboldt's Asie Centrale, Recherches stir les Chorines de Montagnes et in Climatologie comparee (3 vols.. Paris, 1843). This expedition must he regarded as having also led to much 'increase of our knowledge of the earth's magnetism, through the adoption by the emperor of Russia of Humboldt's proposal for the establishment of Magnetic and meteorological stations from Petersburg to Pekin; which was followed, on Humboldt's application• to the duke of Sussex, by the establish ment of similar stations in the southern hemisphere.
The political changes of the year 1830 led to Humboldt's employment in political ser vices. lie had been tong on friendly terms with the members,of the house of Orleans, and therefore, after Louis Philippe ascended the French throne, he was chosen by the Prussia to carry to Paris his recognition of the new sovereign, and was after wards, during the ensuing twelve years, frequently sent to Paris to reside for four or five months. He accompanied the king of Prussia also in visits to England, Denmark, etc. During this time, he published his Examen Critique de la Ge.ogretphw du Nouveau. Conti nent (5 vols., Par. 1835-38).
Humboldt spent the latter years of his long life at Berlin, where he occupied a high position at the Prussian court. His last great work, Cosmos (4 vols., Stuttg. 1845-581. has been unanimously recognized as one of the greatest scientific works ever published, exhibiting in most lucid arrangement many of the principal facts of the physical sciences, and their relations to each other. It has been translated into all the in which a hook of science is required. The germ of the work was the of Nature
(Ansichten der Rater, Stuttg. 1808). Humboldt died May 6, 1859.
It is riot easy to estimate the amount of Humboldt's contributions to science. The geography of Spanish America was most imperfectly known previous to his travels there, during which he astronomically determined more than 700 positions, and he bestowed much labor on the preparation of the maps in which his discoveries were exhibited. His barometrical observatiens :Were. likewise very numerous, as well as his observations on all points conuCeted witiLizietebrologyi To drips we are indebted for the most important generalizations concerning magnetism and also climate, some results of which are exhib ited in the isothermal and other lines which have begun to be drawn in our maps.
Among his botanical works, that on the geography of plants, De Distributione Geo graphied Plantarum secundum, Cali Temperiem et Altitudinem }Iontiurn(Paris, 1817), must be reckoned the most important. It was preceded by an Baal sur la Geographie des Plantes (I'm-is, 1803). The botanical discoveries made by himself and Bonpland in their American travels were given to the world in a number of works by Humboldt and Knuth. published at Paris from 1809 to 1834. Ile gave to the world also his many of them most valuable, which were made at the same time, in zoology and com pa•ative anatomy; and in a magnificent volume, Vues des Cordilleres et Monuments des Potpies Indigenes de Amerique, he directed the attention of Europe to the monuments of a little known antiquity in America, and showed for the first lime the possibility of combining artistic beauty with scientific accuracy. He published in 1823 an Essat Geognostique sur le Gisement des Roches dans les Hemispheres (Paris); and in 1831, _Fragments de Geologie et Climatologie Asiatigue (2 vols., Paris). In 1811 he produced a work on political economy, EssaiFolitigue sur leRoyaumre de in _Nouvelle Espagne (2, vols.). lie obtained distinction also by his labors in the determination of the magnetic equator, and by his observations on electrical eels, and on the respiration of fishes and young crocodiles. See the great biographical work, edited by Bruins, Alexander von Humboldt, Eine wissensehaftliche Biographic (1872; Eng. trans]., 1872).