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of a purely imaginary world, which developed into his Trait é du Monde. Galileo ’ s Dia-
logues on the Two Chief World Systems (1629) had just appeared in Italy, though it had
not reached France. Yet even before Galileo ’ s ecclesiastical troubles, Descartes was already
apprehensive.
Descartes ’ s cautious inquiry alerts us that the mass of related questions we have been
tracking were forming, in his mind, a new approach to natural philosophy that would make
good on his sweeping claim to understand “ all phenomena of nature. ” Beginning in
1619 – 1620 (just after completing his Compendium ), he had begun drafting his Rules for
the Direction of the Mind , but abandoned that work after 1628; his new project seemed to
carry forward the systematic, mathematical thrust of those rules. In his letter, we seem to
see his new world beginning to be synthesized as he struggles with atmospheric and light
phenomena, musical questions, pendulums, and lute strings.
Immediately after asking Mersenne ’ s theological advice, Descartes returns to musical
questions, which now have a dynamic aspect: the use of various intervals depends on how
the melodic lines move , whether they ascend or descend. For guidance, “ I hold to what
[musical] practitioners say. ”^26 Descartes notices that if, “ in a musical concert, the voices
move always equally or become lower and slower gradually, that puts the listeners to sleep;
but if on the contrary one raises the voice suddenly, that wakes them up. ”^27 These musical
issues merge into questions about bodies: “ One can say that a deep sound is more sound
than a high one because it is made by a more extended body, it can be heard from further
away, etc. ” Here the primal quality of extension , so important in Descartes ’ s later philoso-
phy, enters the realm of sound. Returning to whether strings vibrate differently in air than
in a vacuum leads him to questions about balls of different weights and materials falling
from different heights, fundamental for basic mechanics (and for which Galileo had not
yet published his investigations).
Throughout this letter, Descartes moves freely between musical questions, vibrating
strings, and falling bodies, showing how closely these topics are related in his mind and
how helpful he finds passing between them: the coincidence of the pattern of two vibrating
strings can explain consonances between them.^28 Descartes also considers the relation of
contemporary music to that of ancient Greece, the touchstone of music ’ s fabled powers.
His approach is not cerebral but flies free of rules:Regarding the music of the ancients, I believe that it had something more powerful than ours not
because it was more learned, but because it was less, from which it comes about that those who
have a great natural talent for music, not being subject to the rules of diatonic music, do more by
the sole force of imagination, which those cannot do who have corrupted that force by knowledge
of theory. Further, the ears of hearers not accustomed to a music as ordered as ours are much more
easy to surprise. 29Breaking off abruptly, he announces “ I want to start studying anatomy, ” indicating his
nascent interest in human physiology; his next sentence turns to sunspots.^30