So much for the personal history of the most brilliant lights of the time. More instructive will be a review of the musical character of their work. It is the prevailing influence of one or two masters in each period that marks its extent. Its character was formed by that influence, and salient features of the style of each period may be fairly distinguished. The first period was marked by the extreme development of the canon. Perhaps for the benefit of the reader who may not have studied counterpoint it would be well to give here one or two elementary definitions. Imitation, in the words of Sir Frederick A. Gore-Ouseley, is "a repetition, more or less exact, by one voice of a phrase or passage previously enunciated by another. If the imitation is absolutely exact as to intervals it becomes a canon." Canon is the most rigorous species of imitation. Naturally then, as imitation is the foundation of fugal writing, the first occupation of musicians was its perfection. Thus we see that the composers of the first period of the Netherland school were almost wholly engaged in exploring the resources of canonic composition, and the most celebrated of their number, Ockeghem, was he who displayed the greatest ingenuity in this style. To describe the various forms of canonic jugglery invented by Ockeghem and his contemporaries would weary the reader; but a few may be mentioned as examples of the craft exercised at that time. First, there was the "cancriza," or backward movement of the cantus firmus, in which the melody was repeated interval by interval, beginning at the last note and moving toward the first. Second, there was the inverted canon, in which the inversion consisted of beginning at the original first note and proceeding with each interval reversed, so that a melody which had ascended would, in the inversion, descend. In the canon by augmentation the subject reappears in one of the subsidiary parts in notes twice as long as those in which it was originally announced. Conversely in the canon by diminution the subject is repeated in notes of smaller duration than those first used. These four forms are still extant and have been employed by most great composers of modern music from Bach to the present time. The canon by augmentation is often used in choral music, especially in the bass, with superb effect. Indeed all the varieties described are to be found in the music of Handel and Bach, the latter being a complete master of their use in instrumental as well as choral composition.