he never lost a friend) he was almost as famous for his social as for his scientific victories. Yet he never married.
It was with real sorrow that he obeyed the command of his king and left his dearly loved Paris to pass the remainder of his life in Potsdam. He was in the fifty-ninth year of his age, in perfect health and deeply interested in every department of learning as well as in those special fields to which he had given personal attention. A home was provided for him at Potsdam, a liberal salary paid him regularly, so that, barring the demands which the king made upon him for diplomatic services (and these were not infrequent), as a companion of his official visits, or as a visitor at the palace, he was free to pursue his studies. The German public, proud of his renown, rejoiced in his return to his native land and read with increasing interest and enthusiasm whatever came from his pen.
His lectures at Berlin in the winter of 1827 and 1828, which formed the basis of "Cosmos," were heard with astonishment and delight.
A man like Humboldt, so widely known and so thoroughly trained as an explorer and observer, could not long be permitted to remain quiet in any one place. At the request of the Czar of Russia, under his protection and at his expense, with Ehrenberg, the microscopist, Gustav Rose, the chemist, and Menscherlisch, an engineer, he made a rapid but intelligent survey of Asiatic Russia, giving particular attention to the Ural and Aral Mountain chains. It was on this journey that diamonds were discovered in the Ural Mountains and secured to the government for its control and profit. Ehrenberg and Rose published separate accounts of this journey and Humboldt's "Central Asia" is an enlargement and revision of his first report, which appeared simply as a fragment, on the geology and mineralogy of the country.
While in Paris he had experimented with Gay-Lussac on the nature and qualities-of gas, and with him as a companion had visited Rome, where his brother William was the Prussian minister, in order to study magnetism. It would take a good-sized volume to give an account of the various services he rendered the king, and of the journeys he made as a diplomat, nearly always with success, and in the interest of science. He was in the seventy-sixth year of his age when he made public his intention of writing that great work of his life known as "Cosmos." Previous treatises he looked upon as preliminary sketches compared with the work he would now compose and in which he would try to give an accurate and sufficiently full account of all existing scientific knowledge. In this work, while presenting general rather than detailed conclusions or statements, he would show that nature, in spite of her seeming complexity, is yet a unit and governed by a definite and well-ordered plan. A master of the materials furnished by the most eminent scientists of the day, without claiming for himself to be an authority in any single department of science, he believed himself better fitted by reason of