His early studies in this branch are attested by an article in the North American Review for June, 1819, on Du Ponceau's Report on the Languages of the American Indians, and another article in the same Review, for July, 1820, on Dr. Jarvis's Discourse on the Religion of the Indian Tribes of North America. The latter attracted the particular attention of William von Humboldt. The Collections of the Massachusetts Historical Society contain several important communications from him on the Indian languages: in 1822 (Vol. IX. Second Series) an edition of the Indian Grammar of Eliot, the St. Augustin of New England, with Introductory Observations on the Massachusetts Language by the editor, and Notes by Mr. Du Ponceau, inscribed to his "learned friend, Mr. Pickering, as a just tribute of friendship and respect";--in 1823 (Vol. X. Second Series) an edition of Jonathan Edwards's Observations on the Mohegan Language, with an Advertisement and Copious Notes on the Indian Languages by the editor, and a Comparative Vocabulary of Various Dialects of the Lenape or Delaware Stock of North American Languages, together with a Specimen of the Winnebago Language;--in 1830 (Vol. II. Third Series) an edition of Cotton's Vocabulary of the Massachusetts Language. He also prepared Roger Williams's Vocabulary of the Narragansett Indians for the Rhode Island Historical Society. These labors were calculated, in no ordinary degree, to promote a knowledge of our aboriginal idioms, and to shed light on that important and newly attempted branch of knowledge, the science of Comparative Language. Among the Memoirs of the American Academy, published in 1833, (Vol. I. New Series) is the Dictionary of the Abnaki Language, in North America, by Father Sebastian Rasles, with an Introductory Memoir and Notes by Mr. Pickering. The original manuscript of this copious Dictionary, commenced by the good and indefatigable Jesuit in 1691, during his solitary residence with the Indians, was found among his papers after the massacre at Norridgewock, in which he was killed, and, passing through several hands, at last came into the possession of Harvard University. It is considered one of the most interesting and authentic documents in the history of the North American languages. In the Memoir accompanying the Dictionary, Mr. Pickering, with the modesty which marked all his labors, says that he made inquiries for memorials of these languages, "hoping that he might render some small service by collecting and preserving these valuable materials for the use of those persons whose leisure and ability would enable them to employ them more advantageously than it was in his power to do, for the benefit of philological science."