DEAR SIR,--A part of the information of which the expedition of Lewis and Clarke was the object, has been communicated to the world by the publication of their journal; but much and valuable matter yet remains uncommunicated. The correction of the longitudes of their map is essential to its value; to which purpose their observations of the lunar distances are to be calculated and applied. The new subjects they discovered in the vegetable, animal, and mineral departments, are to be digested and made known. The numerous vocabularies they obtained of the Indian languages are to be collated and published. Although the whole expense of the expedition was furnished by the public, and the information to be derived from it was theirs also, yet on the return of Messrs. Lewis and Clarke, the government thought it just to leave to them any pecuniary benefit which might result from a publication of the papers, and supposed, indeed, that this would secure the best form of publication. But the property in these papers still remained in the government for the benefit of their constituents. With the measures taken by Governor Lewis for their publication, I was never acquainted. After his death, Governor Clarke put them, in the first instance, into the hands of the late Doctor Barton, from whom some of them passed to Mr. Biddle, and some again, I believe, from him to Mr. Allen. While the MS. books of journals were in the hands of Dr. Barton, I wrote to him, on behalf of Governor Lewis' family, requesting earnestly, that, as soon as these should be published, the originals might be returned, as the family wished to have them preserved. He promised in his answer that it should be faithfully done. After his death, I obtained, through the kind agency of Mr. Correa, from Mrs. Barton, three of these books, of which I knew there had been ten or twelve, having myself read them. These were all she could find. The rest, therefore, I presume, are in the hands of the other gentlemen. After the agency I had had in effecting this expedition, I thought myself authorized, and, indeed, that it would be expected of me, that I should follow up the subject, and endeavor to obtain its fruits for the public. I wrote to General Clarke, therefore, for authority to receive the original papers. He gave it in the letters to Mr. Biddle and to myself, which I now enclose. As the custody of these papers belonged properly to the War-Office, and that was vacant at the time, I have waited several months for its being filled. But the office still remaining vacant, and my distance rendering any effectual measures, by myself, impracticable, I ask the agency of your committee, within whose province I propose to place the matter, by making it the depository of the papers generally. I therefore now forward the three volumes of MS. journals in my possession, and authorize them, under General Clarke's letters, to inquire for and to receive the rest. So also