Return to Cambridge.--Removal of Collection to New Museum Building. --Distribution of Work.--Relations with his Students.--Breaking out of the War between North and South.--Interest of Agassiz in the Preservation of the Union.--Commencement of Museum Publications. --Reception of Third and Fourth Volumes of "Contributions."--Copley Medal.--General Correspondence.--Lecturing Tour in the West. --Circular Letter concerning Anthropological Collections.--Letter to Mr. Ticknor concerning Geographical Distribution of Fishes in Spain. CHAPTER 20. 1863-1864: AGE 56-57. Correspondence with Dr. S.G. Howe.--Bearing of the War on the Position of the Negro Race.--Affection for Harvard College. --Interest in her General Progress.--Correspondence with Emerson concerning Harvard.--Glacial Phenomena in Maine. CHAPTER 21. 1865-1868: AGE 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. CHAPTER 22. 1868-1871: AGE 61-64. New Subscription to Museum.--Additional Buildings.--Arrangement of New Collections.--Dredging Expedition on Board the Bibb.--Address at the Humboldt Centennial.--Attack on the Brain.--Suspension of Work.--Working Force at the Museum.--New Accessions.--Letter from Professor Sedgwick.--Letter from Professor Deshayes.--Restored Health.--Hassler Voyage proposed.--Acceptance.--Scientific Preparation for the Voyage. CHAPTER 23. 1871-1872: AGE 64-65. Sailing of the Hassler.--Sargassum Fields.--Dredging at Barbados. --From the West Indies to Rio de Janeiro.--Monte Video. --Quarantine.--Glacial Traces in the Bay of Monte Video.--The Gulf of Mathias.--Dredging off Gulf of St. George.--Dredging off Cape Virgens.--Possession Bay.--Salt Pool.--Moraine.--Sandy Point. --Cruise through the Straits.--Scenery.--Wind Storm.--Borja Bay. --Glacier Bay.--Visit to the Glacier.--Chorocua Bay. CHAPTER 24. 1872: AGE 65. Picnic in Sholl Bay.--Fuegians.--Smythe's Channel.--Comparison of Glacial Features with those of the Strait of Magellan.--Ancud. --Port of San Pedro.--Bay of Concepcion.--Three Weeks in Talcahuana.--Collections.--Geology.--Land Journey to Santiago. --Scenes along the Road.--Report on Glacial Features to Mr. Peirce. --Arrival at Santiago.--Election as Foreign Associate of the Institute of France.--Valparaiso.--The Galapagos.--Geological and Zoological Features.--Arrival at San Francisco. CHAPTER 25. 1872-1873: AGE 65-66.