I learn from the Abbe Dobos, (Reflexions sur la Poesie et la Peinture, tom. iii. p. 174, 175,) that the simplicity of the Ambrosian chant was confined to four modes, while the more perfect harmony of the Gregorian comprised the eight modes or fifteen chords of the ancient music. He observes (p. 332) that the connoisseurs admire the preface and many passages of the Gregorian office.