Dewey 1876 Cover

The March "Library Cover Story" on the Library History Buff website (at the bottom of the home page) concerns the cover above. I have been unable to unravel the full story behind this advertising cover which was mailed to Melvil Dewey in Amherst, Massachusetts in what appears to be June or July of 1876. What I have discovered thus far is largely due to Wayne A. Wiegand's book Irrepressible Reformer: A Biography of Melvil Dewey (American Library Association, 1996). The corner card or return address is for the American Metric Bureau, General Office, Tremont Pl., cor. Beacon St., Boston. Melvil Dewey left Amherst in April, 1876 where he had served as Assistant Librarian at Amherst College. He went to Boston to embark on a business arrangement with the the Ginn Company, an educational publisher located at 13 Tremont Place. Dewey was an ardent proponent of the metric system and part of his arrangement with the Ginn Company was to market metric devices. On July 4, 1876, Dewey incorporated the American Metric Bureau. The mystery here is why would a letter from Dewey's Metric Bureau office in Boston be sent to Dewey in Amherst. The cover is one of the favorite items in my collection since it links Dewey and 1876, the year in which he first published his Decimal System and participated in the founding of the American Library Association.