straightline postmark on folded letter to Berwick, Maine, erroneously rated "1.8" [dwt] as the postage should have been 2dwt for a distance of 101-200 miles, very fine, until a United States post office opened there in 1796, Berwick was operated as a private subscription post office serviced by post riders paid for by its patrons, postage was calculated between Boston and the post office nearest to the destination town (in this case, Portland)