What we observe with different nations of the present day, respecting the diversity of musical scales, might evidently also have been observed in ancient time. The Greeks had several kinds of scales, the popularity of which changed at different periods. So also had our forefathers during the Middle Ages. There is no necessity to refer to the Tetrachord of the ancient Greeks and the Hexachord of Guido Aretinus for evidences of the mutability of taste in these matters, since it can be observed sufficiently by referring to the music of nations around us. However, the so-called Modes of our old ecclesiastical music require here, at any rate, a passing notice. Some theorists maintain that our diatonic major scale is alone a true scale, and that any other regular succession of tones in which the two semitones of the diatonic scale occur upon other intervals than 3-4 and 7-8 is, properly speaking, a Mode. According to this doctrine, which was evidently suggested by the ecclesiastical Modes, our minor scale must be called a Mode, and the scales with steps exceeding a whole-tone, of which some examples will presently be given, are Imperfect Modes. It is unnecessary to refute such pedantic definitions; suffice it to remember that they exist. Again, the diatonic major scale is regarded by many musicians as the natural order of intervals on which the compositions must be founded whenever the art of music has attained to a high degree of development, and which will therefore be universally adopted in the course of time. They form this opinion especially from the laws of Acoustics, since the intervals constituting the diatonic major scale are those which as harmonics stand in the most simple relation to the fundamental tone produced by a vibrating body. Here, however, it must be observed that the intervals of our diatonic scale are not all of them precisely the same as those harmonics, but are "tempered;" since, did we tune them pure, as nature gives them, we could not use our system of harmony as it has been developed by our classical composers. Moreover, if the diatonic major scale is thus suggested by nature, the minor scale with its flat third must be more artificial, and less likely to be universally adopted. Howbeit, the minor scale is especially popular, not only with several uncivilized races, but also with several who have cultivated the art of music to a high degree. Some of our most eminent composers have written perhaps more beautiful music in minor than in major keys.