It is a union of the harp with the mechanism of key-action. Harps, in which the strings are plucked with the plectrum, are in some form or other as old as music itself, and appear in the most various shapes in the first dawn of civilisation. The mechanism of the keyboard, which by means of an easy leverage adapted to the human fingers, gives the player control over the sounds of pipes or strings, is not quite so ancient, since it presumes a certain inventive capacity; but it is old enough to be equally beyond our chronological powers. In Europe we find keyed organs as early as the first centuries after Christ. The application of this action to stringed instruments was completed in the monochord. The monochord, an instrument well-known to the earliest theoretical musicians, was a board with a string stretched across it on which the intervals could be clearly marked and sounded by mathematical division: the half marking the octave above the pitch of the whole length of the string; the third part of it giving a fifth above that octave; the quarter part giving a fourth above that fifth, namely a note two octaves above the pitch of the whole string; the fifth part sounding a major third above the last named note, viz., a seventeenth above the pitch of the whole length; and so on. The simple monochord developed itself after the tenth century in two directions, the musical and the technical. Its development was musical, inasmuch as three or four strings took the place of the _one_ in order to produce a chord instead of a simple arpeggio; an aim which the church music attained by the multiplication of instruments sounding only one note each at a time. It was technical, inasmuch as, in place of the constant alteration of the “bridge” which divided the string, _keys_ were introduced, which not only divided the string at the desired spot, by a flat metal pin (called “tangent” from its action in simply “touching” against the wire), but also caused it to sound. With twenty keys and only a few strings, of course it was necessary for several keys to divide the same string, and to sound it at different points in its length; whereby the simultaneous sounding of several notes was brought into the proper limits. Though thus really many-stringed, the instrument still retained its name of _mono_chord. Gradually the number of keys increased, and in increasing proportion the number of strings, which still remained of equal length. About the year 1450, probably, the clavier attained this, its earliest form of the monochord. It served an educational purpose. Virdung, Abbot of Amberg, who in 1511 published his German “Music with Illustrations,” is our authority for the development of the monochord up to the first true clavier-form--that of the _clavichord_--which is nothing more nor less than the many-stringed many-keyed “monochord” which we have just described. The self-contradictory “mono” was