After musicians had once taken the plunge, and dared to make different melodies sound simultaneously, it took them but a comparatively short time (though eras in music, as in geology, are long) to combine the parts in other intervals than the fifth, to use varying intervals in successive chords, to add more voices, and in general to elaborate in every way their tissue of tones. Adopting, with some modifications, the Greek modes as the prescribed orbits of the individual melodies, they produced effects of harmony necessarily very unlike our modern ones, which are built upon the major and minor scales, but nevertheless novel and in their way extremely beautiful. The fabric of the mediæval ecclesiastical music was made up of a succession of shifting chords, each very pure and sweet in itself, yet without those definite connections with its fellows that modern habits of thought demand. The whole effect was curiously kaleidoscopic, mysterious, and vague. Unity depended, not on the piece being in any one key, which it never was, but on the melodies being coherent and expressive. These were the salient features, the harmony was ancillary and incidental. One voice after another came out from the filmy background, sounded for a moment above the rest, and subsided again, to be replaced by another. Not only was there no attempt at a definite series of even sections, built up into recognizable rhythms, such as are indispensable to modern music, but any such effect was studiously avoided. The effort was rather to make the voices interweave inextricably and untraceably. The entire mass was in constant flux and change, a body of lovely and expressive sound, without a single distinct lineament, or any conceivable whence or whither. In Palestrina we have the style at its acme, vague, iridescent, beautiful with a mystical and unearthly beauty. Beyond the point it reached with him, pure polyphonic music, without rhythmic or harmonic definition, could not go. Another critical point was reached, another transformation was imminent.