Like the pitches, the rhythms are also organized serially and strive for contrast amongst the melodies rather than relatedness . Various scales of durations are employed: Fibonacci numbers (1, 2, 3, 5, 8, 13, ... ), arithmetic series (1, 2, 3, 4, 5, ... ), and "second order" arithmetic series, in which the "difference" between consecutive members increases arithmetically (2, 3, 5, 8, 12, 17, ... ). One melody, "Aries", mixes all three of these scale types, at different levels of the durational organization.