Three months after his settlement at Neuchâtel, where eighty louis had been guaranteed to him for three years, he was invited to Heidelberg, to succeed his former professor, Leuckart, in zoölogy. He would receive a salary of five hundred florins, besides about fifteen hundred gulden for lectures and literary work. He declined the honor, because he wished more time to devote to his writing. The following year Neuchâtel purchased his collections in natural history, thus affording him some pecuniary aid in his work.
A serious misfortune now threatened him in the loss of sight. Having injured his eyes by microscopic work, for several months he was shut up in a dark room, practising the study of his fossils by touch alone; by the tongue when the fingers were not sufficiently sensitive to feel out the impression. With great care his eyes improved, so that he was able to use them through life more constantly than most persons.
In October, 1833, when he was twenty-six, Agassiz married Cecile Braun of Carlsruhe, the sister of his life-long friend Alexander. They began housekeeping in a small apartment at Neuchâtel, both practising the closest economy that the books might be carried on; the "Fresh-Water Fishes," and the "Fossil Fishes." She was a skilful artist, had done much work for her brother in botany, and now helped her young husband in drawing and coloring his fishes.
The first number of the "Fossil Fishes" had already appeared, with the following title, which shows the plan of the great work, to which he devoted ten years, from 1833 to 1843:—
"Researches on the Fossil Fishes: comprising an Introduction to the Study of these Animals; the Comparative Anatomy of Organic Systems which may contribute to facilitate the Determination of Fossil Species; a New Classification of Fishes, expressing their relations to the Series of Formations; the Explanation of the Laws of their Succession and Development during all the Changes of the Terrestrial Globe, accompanied by General Geological Considerations; finally, the Description of about a thousand Species which no longer exist, and whose Characters have been restored from Remains contained in the Strata of the Earth."
The work was inscribed to Humboldt. "These pages owe to you their existence; accept their dedication." It met everywhere the most favorable reception. Élie de Beaumont wrote to Agassiz: "It promises a work as important for science as it is remarkable in execution. Do not let yourself be discouraged by obstacles of any kind; they will give way before the concert of approbation which so excellent a work will awaken."
Agassiz had become known to scholars throughout Europe, as an indefatigable worker, but he was still poor. Now and then there came a gleam of sunshine into the straitened life. In 1834, he was greatly surprised to receive from the London Geological Society, through Sir Charles Lyell, the Wollaston prize, of about one hundred and fifty dollars, conferred upon him for his work on fishes.
He writes back to Lyell: "You cannot imagine the joy your letter has given me. The prize awarded me is at once so unexpected an honor and so welcome an aid that I could hardly believe my eyes when, with tears of relief and gratitude, I read your letter. In the presence of a savant, I need not be ashamed of my penury, since I have spent the little I had wholly in scientific researches. I do not, therefore, hesitate to confess to you that at no time could your gift have given me greater pleasure. Generous friends have helped me to bring out the first number of my 'Fossil Fishes;' the plates of the second are finished, but I was greatly embarrassed to know how to print a sufficient number of copies before the returns from the first should be paid in. The text is ready also, so that now, in a fortnight, I can begin the distribution, and, the rotation once established, I hope that preceding numbers will always enable me to publish the next in succession without interruption. I even count upon this resource as affording me the means of making a journey to England before long."
In August, 1834, Agassiz went to England, and there formed delightful friendships with such men as Lyell, Murchison, Buckland, and others. He was allowed to cull, from sixty or more collections, some two thousand fossil fishes, and deposit them in the Somerset House in London, where Mr. Dinkel, the artist, remained for several years at work, copying.
In the summer of 1836, he began his remarkable study of the glaciers. He was so cramped for means to carry forward his "Fossil Fishes," that it seemed probable that he must discontinue it, when opportunely his original drawings were purchased by Lord Francis Egerton and given to the British Museum. The financial condition was thus bettered for a time.