Returning to the United States in 1820, he was appointed professor of geology and mineralogy, and college librarian at Harvard. In 1823, having resigned his chair in Harvard, he, in connection with George Bancroft, the historian, established Round Hill School at Northampton, Massachusetts. The plan of the institution was novel, and based on an examination of the best English and German systems of education. After Bancroft's departure from the school in 1830, Cogswell continued the work. It was too much for him alone, and he closed the doors of the school in 1834. He then assumed the charge of a similar institution in Raleigh, North Carolina. Ill health and incompatibility with Southern culture led to his resignation after two years at Raleigh.
Editor and librarian
In 1836, he entered the family of banker Samuel Ward in New York City. Three of Ward's sons had been students at Round Hill School. Cogswell also became editor of the New York Review, one of the leading American critical journals of the time. He remained as editor until its suspension in 1842. Through Ward, he became the friend and companion of John Jacob Astor, upon whom he urged the project of a library. Succeeding in this promotion, Cogswell, in conjunction with Astor, Washington Irving and Fitz-Greene Halleck, arranged the plan of the Astor Library. With Halleck, Irving, and others, Cogswell was appointed a trustee of the fund for its creation. When Washington Irving was appointed minister to Spain, he was anxious that his friend Cogswell should accompany him as secretary of legation, and accordingly wrote to Washington, requesting his appointment. “He is,” said Irving, “a gentleman with whom I am on terms of confidential intimacy, and I know no one who, by his various acquirements, his prompt sagacity, his knowledge of the world, his habits of business, and his obliging disposition, is so calculated to give me that counsel, aid, and companionship, so important in Madrid, where a stranger is more isolated than in any other capital of Europe.” Cogswell received the appointment, and would probably have accepted it, but, Astor finding that he was likely to lose his invaluable services, made him superintendent of the new library. After the rich merchant's death, in 1848, Cogswell traveled to Europe to purchase books. Cogswell made many acquaintances among European intellectual elites during his frequent visits to Europe, including Johann von Goethe, Alexander von Humboldt, Pierre-Jean de Béranger, Lord Byron, and Walter Scott. His general bibliographical knowledge was of great service to the Astor Library, one great work undertaken by him being the preparation of an analytical and alphabetical catalogue of the collection. He also gave the Astor Library his own valuable series of works relating to bibliography, as he had before united with a friend in presenting Harvard with a rare cabinet of minerals and numerous botanical specimens. He continued the duties of superintendent until his retirement due to old age in 1861. Cogswell returned to Massachusetts—settling in Cambridge, Massachusetts. He resigned as a Trustee of the Astor library in 1863. He died November 26, 1871 in Cambridge.
