Double, and even triple, stringing had been introduced in clavichords, and was continued in pianos. The elder Stein invented the shifting of the keyboard which causes the hammer to strike only one string instead of three. This contrivance is used by some of the best makers of the present day. Stein also improved the "escapement," the arrangement by which the hammer falls back the instant it has struck the string, and this, with other features of the action, was further developed by Streicher, so that the Viennese pianos became famous for the extreme lightness of their touch, and music written by composers in that part of the world was designed to meet this quality. The English pianos, meanwhile, were built with heavier strings and a deeper fall of the hammer, so that greater sonority was attainable, and composers wrote for them bold passages in successions of heavy chords, which would have gone for nothing on a Viennese piano. At the very outset Cristofori had to shift the pins to which the wires were attached, from the soundboard, which would not stand the strain, to a separate rail. It became necessary to brace the whole interior with steel arches, of whose inventor there is no record, but Broadwood was the first to introduce the method now employed. Sebastien Érard, a celebrated French maker, introduced many improvements in the action and devised what was called then the "celeste" pedal, by which the hammers struck a strip of leather interposed between them and the strings. The leather is now replaced by felt. The iron frame, now replaced by steel and found in all fine pianos, was invented by Alpheus Babcock of Boston in 1825. Frederick W. C. Bechstein, of Berlin, in 1855 combined iron frames and the powerful English action in his instruments, and took a commanding position. The upright piano was patented Feb. 12, 1800, by John Isaac Hawkins of Philadelphia. Subsequent developments in the piano have been of too wide a range to be mentioned in the space at my command, and at any rate have all been in the nature of improvements,--highly important, indeed, but without radical departure from the fundamental features of the instruments.