Newton and the Mystery of the Major Sixth 131
case of light, his use of a similar proportion allows him to subsume the major sixth in an
overarching octave.^24 His reinterpretation sets forth a rival Keplerian “ third law, ” here for
the harmonies of the colored rings, rather than of the planets.
Having done so, he seems to have satisfied himself that the major sixth is a masked
form of the octave. Thus, he was not inclined to interpret the major sixth as having some
important significance of its own, much less that it could be interpreted in terms of a wave
theory of light. Nor did those who followed him immediately notice this mystery. For
instance, in 1712 Nicolas Malebranche argued that “ different colors consist only in the
different frequency of the pressure vibrations of subtle matter, as different tones of music
result only from the different frequency of the vibration of gross air. ”^25 Thus, Newton ’ s
analogy persists in Malebranche ’ s wave account, which incorporates Newton ’ s octave of
color without noticing the problem of the major sixth. Voltaire also featured “ the Resem-
blance between the seven Primitive Colours and the seven Notes in Musick ” in his popular
treatment of Newtonian philosophy ( figure 8.5 ).^26
The picture was so beautiful, the analogy with the octave so fetching, that all trace of
the troubling major sixth was mostly forgotten until Leonhard Euler and Thomas Young
took note of it decades later, as we shall see. For Newton himself, other more weighty
arguments and concerns may have relegated this musical puzzle to the sidelines. His
opposition to the wave theory of light was long considered and deeply held; his optical
writings are far greater in volume than the few pages he devoted to music in his youth.
Yet musical theory supported his interest in the importance of ratios as applied to physical
phenomena and thus was a helpful touchstone for his mathematical natural philosophy. In
later life, he remarked that “ Pythagoras ’ s Musick of the Spheres was gravity. ”^27 Though
Newton took music sufficiently seriously to register the mysterious major sixth, in the end
his desire to lay the mystery to rest may have missed its surprising import because he did
not take music seriously enough.