"The penny post inaugurated and administered by Rowland Hill required the adoption of four novel principles: (1)prepayment of postage, (2) payment by weight instead of by the number of sheets, (3) the use of envelopes, (4) the use of adhesive stamps on letters. Prior to this reform, for example, the use of an envelope would have been a novelty to most letter-writers and entailed double postage." -- PMM 306.