That
motion is relative was known to the Greeks. Copernicus cites the Aeneid on the
point-of-view that the land slips away as the ship moves past it. (page 519,
EB “Great Books” edition). Fire burns brighter at lower altitudes; and when
carried to higher altitudes, the fire dies down. (Book I Section; 8. 520, EB).
Copernicus says as a matter of fact, not argument, that the planets are “dark
bodies” that shine by reflected light. (Book I Section 10; Page 521 EB).
In our era, in school, we learn that Galileo discovered that bodies accelerate when they fall, contrary
to Aristotle’s claim that they fall at a constant velocity, determined by their
weight. In fact, Copernicus acknowledged
the acceleration of free fall. In the original edition, Copernicus wrote: “Et quaecunquae decidunt a principio lentum
facientia motu velocitatem augent cadendo.” That is rendered today as: "And those which fall downward possess a slow movement at the beginning
but increase their velocity as they fall."(Book I Section 8. Page 520
EB) See also Book III Section 3 where he mentions
the motion of a pendulum being faster at the bottom of the arc and slower at the tops.
The
acceleration of a body in free fall apparently was known to the “Oxford
calculators” of the Merton School who worked about 1325-1350. They developed a geometric solution for the “mean
rate.” The “mean rate” is the average of the initial velocity and the final velocity.
Galileo cited their results in The Two
New Sciences, Third Day, Theorem I, Proposition I.
Most
of On the Revolution of Heavenly Spheres
is tedious for anyone not passionate about the geometric arguments. Copernicus
had to prove his claims to the thinkers of his time in the language of their
culture. The same was true of Newton’s Principia.
Richard Feynman attempted to recreate a proof for his own lecture and found
that he could not because he did not know enough geometry: we do it all with
calculus now. Copernicus provides extensive ephemeris tables of his own
measurements. But he also worked out trigonometric tables of “half-sines.” (We
call it the “sine” in school, but it is actually the half.) And he showed how his sun-centered circles explain
all of the apparent motions in longitude, oppositions, retrograde, etc. And he
often cited Ptolemy, who also made good measurements of the same events.
Copernicus’s
On the Revolution of Heavenly Spheres is
easily available in modern translations. Several archives have full scans of
the original 1543 publication.
The ADS
wishes to acknowledge the Lehigh University,
Digital Library ("The Problem of the Planets")
for providing the scans of the book. (http://digital.lib.lehigh.edu/planets/ )
The
Smithsonian also has one of the 1543 editions in its Dibner collection. (See https://airandspace.si.edu/exhibitions/explore-the-universe/online/kiosks/dibner/)
The image
title says: Nicholas Copernicus, De Revolutionibus Orbium Coelestium Libri VI
(Basel, 1543), but the title page says “Norimbergae” i.e., “Nuremberg.”
PREVIOUSLY ON NECESSARY FACTS
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