The mysterious power of music has intrigued thinkers across the centuries. Plato described a universe in which Sirens situated atop the rings of the cosmic whorl each sing a single note from a great scale, together producing concords that can transport mortals to the heavenly regions. In our own time we tend to use other metaphors to explain the phenomenon -- with terms like "brain scan" and "beta-endorphins" -- but when listening to an exquisite piece of music, who could deny the emotional truth of Plato's vision? Perhaps we respond so forcefully because, as Clement of Alexandria put it, the human body is itself a musical instrument. That was the view not only of the ancient Greeks but also of the Indian masters who strongly influenced Michael Harrison's musical development. Both proposed deep connections between the arrangements of tones and the human condition, and pointed to the most fundamental musical relationships -- those defined by ...