Music and the Making of Modern Science

Descartes’s Musical Apprenticeship 99

our sensation of light as an experience of pressure registered by the eyes, essentially sonic

in its dynamics. For instance, he depicts the refraction of light rays by the reciprocal

pushing and impeding of the little balls of world-fluid ( figure 6.5 ). In his later develop-

ments of this idea, he ascribed the phenomenon of color to the different states of spin of

these interacting balls, which he compares to spinning tennis balls.

On the largest scale, Descartes uses his sonic world-fluid to explain the motions of the

planets in terms of a series of vortices, which carry around the visible planetary bodies

( figure 6.6 ). His picture had the intuitive merit of explaining how the planets could move

in seemingly empty space by showing the motions of the invisible fluid that guide them,

those closer to the center of the vortex moving more swiftly about that center than those

farther away, as is true of the planets with respect to the sun. In Descartes ’ s picture, the

sun must necessarily stand at the center of our vortex, so that his world is necessarily

Copernican, probably the crucial fact he wished to conceal by presenting a purely imagi-

nary world.

The impending controversy brought him back to this all-too-human Earth. Though in

July 1633 he had written Mersenne that his treatise “ is just about finished, ” in November

of that year he learned the news of Galileo ’ s condemnation, which “ has so astonished me

that I am almost resolved to burn all my papers, or at least not to let anyone see them. ”^36

Descartes ’ s new physics required the motion of the Earth and offered an alternative to

Aristotelian physics. Even Galileo, convinced Copernican though he was, had no account

of an alternative physics that might support the new picture of the universe that shattered

the Aristotelian separation between physis and the perfection of the heavens ( ouranos ).

Though Kepler had offered speculations about anima motrix , a “ moving spirit ” analogous

to magnetic power emanating from the sun capable of moving the planets around it, he

Figure 6.4

Descartes ’ s illustration from Le Monde , showing how horizontal pressure to the right on the “ parts ” of a fluid

marked 1, 2, 3, 4, 5 will in turn move those marked 10, 20, 30, 40, 50 to the right.