A musical instrument containing all conceivable perfections for performance, we do not yet possess. Such an instrument would be required to yield not only Whole-Tones and Semitones, but likewise Demi-semitones, Semidemi-semitones,--in short, every modification of an interval which the performer desires. It must have the greatest compass obtainable in tones. All its tones must be of equal power, sonorousness and beauty. The sustaining, the increasing and decreasing in loudness, must be possible with each tone separately, at the option of the performer, even in harmonious combinations. Likewise the difference in manner of expression, such as legato, staccato, etc., must be thus obtainable. The greatest possible difference in the quality of sound (_timbre_) must be at the command of the performer for any tone which he wishes to be thus affected. The instrument must permit the simultaneous sounding of as many of its tones as the performer desires, whatever their distance from each other may be, and this must be achievable by him with about the same facility as he requires for the production of a single tone. The instrument must be playable by only one performer; it must not present any extraordinary difficulty to musicians to play it well; and it must permit being easily kept in tune. Perhaps the organ approaches the nearest to this perfection, but is still far from it. The violin and the violoncello are in some respects ahead of all--at any rate, as regards delicacy of expression. But, fascinating though it may be to depict such a nearly perfect musical instrument of the Future, the real substitutes of our present contrivances, a century or two hence, will probably be very different from our ideal, especially if we found our speculation on the impression that our Tonal System is the only right one, and that our diatonic major scale will be as everlasting as a mathematical truth, or as the axiom that two and two are four.