Humboldt and Guizot were like brothers, and for forty years corresponded affectionately with each other. Arago he held "dearest in this life." His last letter to Arago, "small in size but so full of matter," was the greatest comfort to the dying astronomer. During all these busy twenty years he had honors heaped upon him. He was offered the position of Ambassador to Vienna, but declined. He accompanied the King of Prussia to England in 1814, and was with him at the peace of Aix-la-Chapelle and at the Congress of Verona. Busy as he was, he seemed to find time to befriend everybody, especially young men. Liebig says in the preface of his work dedicated to Humboldt: "During my residence in Paris, I gave a course of lectures at the Academy in the winter of 1823-4, upon an analytic investigation of Howard's fulminating mercury and silver--my first effort in the field of science. "At the close of the sitting of March 22, 1824, while busy packing up my apparatus, a gentleman came up to me from among a group of academicians, and entered into conversation. In the most winning manner, he made inquiry as to the objects of my study, my present occupations, and the plans I had laid for the future. We separated without my knowing to whom I was indebted for this kind expression of interest, for my shyness and inexperience had not allowed me to make the inquiry. "This conversation laid the foundation of my future career, for I thus acquired a kind friend and a powerful patron in my scientific undertakings.... "From that time all doors were thrown open to me, I had access to every institution and every laboratory: the great interest you took in me procured the love and intimate friendship of my instructors, Gay-Lussac, Dulong, and Thénard, to all of whom I became deeply attached. The confidence which you accorded me was the means of my introduction into a sphere of labor which during the last sixteen years it has ever been my ambition worthily to occupy." When Agassiz was a poor medical student in Paris, Humboldt visited him. Agassiz says:-- "After a cordial greeting, he walked straight to what was then my library--a small book-shelf containing a few classics, the meanest editions, bought for a trifle, along the quays, some works on philosophy and history, chemistry and physics, his own 'Aspects of Nature,' 'Aristotle's Zoölogy,' 'Linnæus' Systema Naturæ,' in several editions, 'Cuvier's Règne Animal,' and quite a number of manuscript quartos, copies which, with the assistance of my brother, I had made of works I was too poor to buy, though they cost but a few francs a volume....