Moving the Immovable 47
Presenting his own cosmological assumptions at the beginning of his Almagest , Ptolemy
made no such reference to harmony, though he refers to mathematical theories as “ beautiful
[ kalon ] ” and praises “ the contemplation of the eternal and unchanging, ” such as his treatise
presents.^19 In contrast, Copernicus is evidently arguing against the general opinion that
heliocentrism is “ quite ridiculous, ” as Ptolemy put it, controverting common sense and
plain reason. 20 Copernicus ’ s language of harmony aims to reconcile his readers to these
dissonances, even to help them appreciate their richness and surpassing beauty. His invoca-
tion of harmony ultimately stems from the musically formed cosmos of Plato, as do so
many later invocations of harmony we will consider in science, down to the present day.
Copernicus ’ s rhetoric relies on the implicit interconnection between astronomy and the
rest of the quadrivium. Where “ symmetry ” tends to have visual connotations, Copernicus ’ s
word symmetria also has the specifically geometric meaning of commensurability.^21
That is, the size of each planet ’ s sphere can be expressed in terms of the Earth – sun mean
distance as an astronomical unit. By pointedly connecting the technical terms symmetria
and harmonia , Copernicus signals the linkage between arithmetic and music he considers
a capital feature of heliocentrism. In his dedicatory letter to Pope Paul III, Copernicus also
mentions the secretive practices of the Pythagoreans; his original manuscript emphasized
these Pythagorean connections even more strongly.^22 He thereby brings to mind their
heliocentric cosmology, as well as their quest to understand the harmonia of the cosmos
in musical ratios, both important precedents for his heliocentric symmetria.^23
In different ways, Copernicus ’ s early readers recognized and amplified the musical
context of harmonia. Even before the publication of De revolutionibus , Copernicus ’ s
disciple Rheticus explained in his Narratio prima (1540) what his teacher meant by “ an
absolute system ” in which “ the order and motion of the heavenly spheres agree. ” Writing
about earlier astronomers (such as the Arab Albategnius), Rheticus remarks that “ we
should have wished them, in establishing the harmony of the motions, to imitate the musi-
cians who, when one string has either tightened or loosened, with great care and skill
regulate and adjust the tones of all the other strings, until all together produce the desired
harmony, and no dissonance is heard in any. ”^24 In favor of the heliocentric view, Rheticus
notes that “ all the celestial phenomena conform to the mean motion of the sun and that
the entire harmony of the celestial motions is established and preserved under its control. ”
Because Rheticus writes explicitly to explain the system of “ my teacher, ” we might take
these expressions as also having Copernicus ’ s implicit approval. They further amplify the
language of “ harmony ” by adding further details of its musical implications, down to the
tuning of the strings to avoid dissonance.
Johannes Praetorius ’ s Compendiosa enarratio Hypothesium Nic. Copernici ( Compendi-
ous Narration of the Hypothesis of Nicolaus Copernicus , 1594) praises the heliocentric
system because “ this symmetry [ simmetria ] of all the orbs appears to fit together with the
greatest consonance so that nothing can be inserted between them and no space remains
to be filled. ” The explicitly musical term “ consonance ” expands the mathematical notion