He also opened an elaborate correspondence with such persons as were best acquainted with the Indian tribes in different sections of the country.[23] The replies to these various queries were few in number, but the practical plan, adhered to in substance, has resulted in the collection by the Smithsonian Institution of a very large number of Indian vocabularies.[24] This class of investigation, in its ample scope for original research and the ascertainment of principles by analysis and analogic expression, was peculiarly agreeable to Mr.Gallatin.His friend, du Ponceau,[25] who served in the American war as the secretary of Steuben, and was now established in Philadelphia, was likewise deeply engaged in philologic studies; in 1819 he had published a memoir of the construction of the languages of the North American Indians, which he followed later with other papers of a similar nature, among which were a "Grammar of the Languages of the Lenni Lenape or Delaware Indians," and a memoir on the grammatical system of the languages of the Indian tribes of North America, a learned and highly instructive paper, which took the Volney prize at Paris.
In 1836 Mr.Gallatin's original paper, contributed to Balbi, amplified by subsequent acquisitions, was published by the American Antiquarian Society of Worcester, in the first volume of its Transactions.

It was entitled "A Synopsis of the Indian Tribes, within the United States east of the Rocky Mountains, and in the British and Russian Possessions in North America." This elaborate inquiry, the foundation of the science in America, was intended originally to embrace all the tribes north of the Mexican semi-civilized nations.

From the want of material, however, it was confined at the southward to the territory of the United States, and eastward of the Rocky Mountains.

It included eighty-one tribes, divided into twenty-eight families, and was accompanied by a colored map, with tribal indications.

The result of the investigation Mr.Gallatin held to be proof that all the languages, not only of our own Indian tribes, but of the nations inhabiting America from the Arctic Ocean to Cape Horn, have a distinct character common to all.