Chapter 21: 1865-1868: Aet. 58-61.
- Letter to his mother announcing journey to Brazil. -- sketch of journey. -- kindness of the Emperor. -- liberality of the Brazilian government. -- correspondence with Charles Sumner. -- letter to his mother at close of Brazil journey. -- letter from Martius concerning journey in Brazil.--return to Cambridge. -- lectures in Boston and New York. -- summer at Nahant. -- letter to Professor Peirce on the Survey of Boston Harbor. -- death of his mother. -- illness. -- correspondence with Oswald Heer. -- summer journey in the West. -- Cornell University. -- letter from Longfellow.
The next important event in the life of Agassiz, due in the first instance to his failing health, which made some change of scene and climate necessary, is best announced by himself in the following letter.
 The story of this expedition has been told in the partly scientific, partly personal diary published after Agassiz's return, under the title of ‘A Journey in Brazil,’ and therefore a full account of it here would be mere repetition. He was absent sixteen months. The first three were spent in Rio de Janeiro, and in excursions about the neighborhood of her beautiful bay and the surrounding mountains. For greater efficiency and promptness he divided his party into companies, each working separately, some in collecting, others in geological surveys, but all under one combined plan of action. The next ten months were passed in the Amazonian region. This part of the journey had the charm of purely tropical scenery, and Agassiz, who was no less a lover of nature than a naturalist, enjoyed to the utmost its beauty and picturesqueness. Much of the time he and his companions were living on the great river itself, and the deck of the steamer was by turns laboratory, dining-room, and dormitory. Often, as they passed close under the banks of the river, or between the many islands which break its broad expanse into narrow channels, their improvised working room was overshadowed by the lofty wall  of vegetation, which lifted its dense mass of trees and soft drapery of vines on either side. Still more beautiful was it when they left the track of the main river for the water-paths hidden in the forest. Here they were rowed by Indians in ‘montarias,’ a peculiar kind of boat used by the natives. It has a thatched hood at one end for shelter from rain or sun. Little sun penetrates, however, to the shaded ‘igarape’ (boat-path), along which the montaria winds its way under a vault of green. When traveling in this manner, they stopped for the night, and indeed sometimes lingered for days, in Indian settlements, or in the more secluded single Indian lodges, which are to be found on the shores of almost every lake or channel. In this net-work of fresh waters, threading the otherwise impenetrable woods, the humblest habitation has its boat and landing-place. With his montaria and his hammock, his little plantation of bananas and mandioca, and the dwelling, for which the forest about him supplies the material, the Amazonian Indian is supplied with all the necessities of life. Sometimes the party were settled, for weeks at a time, in more civilized fashion, in the towns or villages on the banks of the main  river, or its immediate neighborhood, at Manaos, Ega, Obydos, and elsewhere. Wherever they sojourned, whether for a longer or a shorter time, the scientific work went on uninterruptedly. There was not an idle member in the company. From the time he left Rio de Janeiro, Agassiz had the companionship of a young Brazilian officer of the engineer corps, Major Coutinho. Thoroughly familiar with the Amazons and its affluents, at home with the Indians, among whom he had often lived, he was the pearl of traveling companions as well as a valuable addition to the scientific force. Agassiz left the Amazonian valley in April, and the two remaining months of his stay in Brazil were devoted to excursions along the coast, especially in the mountains back of Ceara, and in the Organ mountains near Rio de Janeiro. From beginning to end this journey fulfilled Agassiz's brightest anticipations. Mr. Thayer, whose generosity first placed the expedition on so broad a scientific basis, continued to give it his cordial support till the last specimen was stored in the Museum. The interest taken in it by the Emperor of Brazil, and the liberality of the government toward it, also facilitated all Agassiz's aims  and smoothed every difficulty in the path. On starting he had set before himself two subjects of inquiry. These were, first, the freshwater fauna of Brazil, of the greater interest to him, because of the work on the Brazilian Fishes, with which his scientific career had opened; and second, her glacial history, for he believed that even these latitudes must have been, to a greater or less degree, included in the ice-period. The first three months spent in Rio de Janeiro and its environs gave him the key to phenomena connected with both these subjects, and he followed them from there to the head-waters of the Amazons, as an Indian follows a trail. The distribution of life in the rivers and lakes of Brazil, the immense number of species and their local circumscription, as distinct faunae in definite areas of the same water-basin, amazed him; while the character of the soil and other geological features confirmed him in his preconceived belief that the glacial period could not have been less than cosmic in its influence. He was satisfied that the tropical, as well as the temperate and arctic regions, had been, although in a less degree, fashioned by ice. Just before leaving the United States he received a letter of friendly farewell from  Charles Sumner, and his answer, written on the Rio Negro, gives some idea of the conditions under which he traveled, and of the results he had obtained. As the letters explain each other, both are given here.
The repose of the return voyage, after sixteen months of such uninterrupted work, and of fresh impressions daily crowding upon each other, was most grateful to Agassiz. The  summary of this delightful journey may close as it began with a letter to his mother.
The following letter from old Professor Martius in Munich, of uncertain date, but probably in answer to one of March, 1866, is interesting, as connecting this journey with his own Brazilian expedition almost half a century before.
Agassiz arrived in Cambridge toward the end of August, 1866. After the first excitement of meeting family and friends was over, he took up his college and museum work again. He had left for Brazil at the close of a course before the Lowell Institute, and his first public appearance after his return was on the same platform. The rush for tickets was far in excess of the supply, and he was welcomed with the most ardent enthusiasm. It continued unabated to the close, although the  lectures borrowed no interest from personal adventure or incidents of travel, but dealt almost wholly with the intellectual results and larger scientific generalizations growing out of the expedition. Later in the winter he gave a course also at the Cooper Institute, in New York, which awakened the same interest and drew crowds of listeners. The resolution offered by Bancroft, the historian, at the close of the course, gives an idea of its character, and coming from such a source, may not unfitly be transcribed here. Resolved, That the thanks of this great assembly of delighted hearers be given to the illustrious Professor Agassiz, for the fullness of his instruction, for the clearness of his method of illustration, for his exposition of the idea as antecedent to form; of the superiority of the undying, original, and eternal force over its transient manifestations; for happy hours which passed too rapidly away; for genial influences of which the memory will last through our lives. All his leisure hours during the winter of 1867 were given to the review and arrangement of the great collections he had brought home. 
The summer of 1867 was passed very tranquilly at his Nahant laboratory, in that quiet work with his specimens and his microscope which pleased him best. The following letter  to Professor Benjamin Peirce, who was then Superintendent of the Coast Survey, shows, however, his unfailing interest in the bearing of scientific researches on questions of public utility.
This year closed for Agassiz with a heavy sorrow. His mother's health had been failing of late, and November brought the news of her death. Separated though they were, there had never been any break in their intercourse. As far as he could, he kept her advised of all his projects and undertakings, and his work was no less interesting to her when the ocean lay between them than when he could daily share it with her. She had an unbounded sympathy with him in the new ties he had formed in this country, and seemed indeed as  intimately allied with his later life here as with its earlier European portion. His own health, which had seemed for a time to have regained the vigor of youth, broke down again in the following spring, and an attack about the region of the heart disabled him for a number of weeks. To this date belongs a short correspondence between Agassiz and Oswald Heer. Heer's work on the Fossil Flora of the Arctics had recently appeared, and a presentation copy from him reached Agassiz as he was slowly regaining strength after his illness, although still confined to the house. It could not have come at a happier moment, for it engrossed him completely, and turned his thoughts away from the occupations which he was not yet allowed to resume. The book had a twofold interest for him: although in another branch of science, it was akin to his own earlier investigations, inasmuch as it reconstructed the once rich flora of the polar regions as he himself had reconstructed the fauna of past geological times; it clothed their frozen fields with forests as he had sheeted now fertile lands with ice. In short, it appealed powerfully to the imagination, and no child in the tedious hours of convalescence was ever more beguiled by a  story-book than he by the pictures which this erudite work called up.
Shortly after Agassiz's recovery, in July, 1868, he was invited by Mr. Samuel Hooper to join a party of friends, tired members of Congress and business men, on an excursion to the West, under conditions which promised not only rest and change, but an opportunity for studying glacial phenomena over a broad region of prairie and mountain which Agassiz had never visited. They were to meet at Chicago, keep on from there to St. Paul, and  down the Mississippi, turning off through Kansas to the eastern branch of the Pacific Railroad, at the terminus of which they were to meet General Sherman with ambulances and an escort for conveyance across the country to the Union Pacific Railroad, returning then by Denver, Utah, and Omaha, and across the State of Iowa to the Mississippi once more. This journey was of great interest to Agassiz, and its scientific value was heightened by a subsequent stay of nearly two months at Ithaca, N. Y., on his return. Cornell University was then just opened at Ithaca, and he had accepted an appointment as non-resident professor, with the responsibility of delivering annually a course of lectures on various subjects of natural history. New efforts in behalf of education always attracted him, and this drew him with an even stronger magnet than usual, involving as it did an untried experiment—the attempt, namely, to combine the artisan with the student, manual labor with intellectual work. The plan was a generous one, and stimulated both pupils and teachers. Among the latter none had greater sympathy with the high ideal and broad humanity of the undertaking than Agassiz.3  Beside the enthusiasm which he brought to his special work, he found an added pleasure at Cornell in the fact that the region in which the new university was situated contained another chapter in the book of glacial records he had so long been reading, and made also, as the following letter tells us, a natural sequence to his recent observations in the West.
Of about this date is the following pleasant letter from Longfellow to Agassiz. Although it has no special bearing upon what precedes, it is inserted here, because their near neighborhood and constant personal intercourse, both at Cambridge and Nahant, made letters rare between them. Friends who see each other so often are infrequent correspondents.