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.[4] 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.