The Competitiveness of Nations in a Global Knowledge-Based Economy
Edgar Zilsel
Copernicus and
Mechanics
Journal of the History of Ideas,
1 (1
Jan. 1940, 113-118.
Copernicus overthrew the medieval conception of the
solar system by starting from the scanty reports on heliocentric theories in
antiquity, by specifying the implications of these geometrically in every
detail, and by thus furnishing the exact foundations for ephemerides that far
surpassed the exactness of the older tables of planetary movements based on the
theory of Ptolemy. 1 His outstanding contribution to astronomy was a
mathematico-geometrical one. It is,
however, sometimes not sufficiently noticed how far removed Copernicus still is
from modern physical and especially mechanical thinking. A few remarks on this point, therefore,
may be useful. They refer to the
first book of De Revolutionibus Orbium Coelestium (1543), in which
Copernicus explains the basic ideas of his theory and
where,
1 Cf. Angus Armitage: Copernicus. The Founder
of Modern Astronomy.
113
consequently, Pythagorean and Scholastic ideas
predominate. Ancient and medieval
philosophic ideas recede into the background in the following five books (II-VI)
in which the mathematical details are explained.
2
(1) Copernicus uses again and again concepts of value in
his general arguments. The third
sentence of Book I asks the rhetorical question: “What is more beautiful than
the sky?... Because of its preeminent excellence most of the philosophers have
called it the Visible God.” In
chapter 8 he supports the statement of the immobility of the sun in the
following way (p. 24, 11. 2 ff.): “Furthermore the condition of
immobility is considered more noble and divine than the condition of change and
instability which, therefore, 3
is more fitting to the earth than to the universe. I add that it would seem rather absurd to
ascribe movement to the containing and locating and not to the contained and
located, which is the earth.” In
chapter 10 he explains (p. 30, 11. 1 ff.): “The sun is stationed
(residet) in the middle of the universe. In this most beautiful temple who could
put this lamp in another or better place than the one from which it can
illuminate the whole universe at once?” The sun, he continues, therefore is
called by some “mind” and “ruler,” and he ends by quoting the chief authority of
occult science, alchemy, and Neo-Platonism: “Trismegistus calls the sun the
Visible God, Sophocles’ Electra, Him who sees everything. The sun, indeed, sitting on a royal
throne rules (gubernat) the family of stars moving around
it.”
(2) Copernicus is inclined to apprehend inanimate
objects as living beings striving to reach aims. Sometimes he expresses himself in an
almost animistic way, more often he gives teleological explanations in the more
rational way of Aristotle and the Scholastics. A few sentences after the passage just
quoted he remarks (p. 30, line 9): “The Earth conceives from the Sun and is
impregnated with annual birth.” In
chapter 1 he explains the spherical form of the universe as follows (p. 11):
“This form is the most perfect one, does not need any joint (nulla indigua
compagine),… and is the most capacious figure… All objects strive
(appetant) to be bounded in this way. This is seen in drops of water and other
liquids when they wish (cupiunt) to be bounded by themselves.” Gravity he explains in the following way
(chap. 9, p. 24, line 25): “I think gravity is nothing else but a natural
appetency (appetentia) given to the parts by the divine providence of the
maker of the universe in order that they may establish their unity and wholeness
(ut in unitatem integritatemque suam se confer-
2. All quotations from Dc Revolutionibus refer to
the Thorn edition, 1873 (ed. M. Curtze).
3. The idea that immobility is nobler than movement is
Platonic and Pythagorean (cf. the well-known Pythagorean table of values,
Diels, Fragmente der Vorsokratiker 45 B 5). Ultimately it goes back to the Eleatic
school (Xenophanes, Diels FVS 11 B 26).
ant), by
combining in the form of a sphere. It is probable that this affection
(affectionem) also belongs to the sun, the moon, and the planets in order
that they may, by its efficacy, remain in their roundness (ut eius efficacia
in… rotonditate permaneant).” On the phenomenon of terrestrial
gravitation he says (chap. 7, p. 19, line 28 : “The element of the earth is the
heaviest, and all heavy things are driven towards it, striving (contendentia)
to its innermost center.”
(3) Closely related to this teleological conception of
nature is the opinion of Copernicus that objects of the same kind exert
“sympathetic” influences on each other. In chapter 8 he discusses the fact that
the surrounding air rotates with the earth and gives two explanations which he
considers to be equally admissible, a medieval-sympathetic one and a modern
mechanical one. The air rotates, he
explains (p. 22, 11. 18 ff.), “either because it is mixed with earthen
and watery matter and, therefore, follows the same nature as the earth
(eandem sequatur naturam quam terra), or because the motion of the air is
acquired and the air participates in it without resistance, since the air is
contiguous to the constantly rotating earth.” A few lines later, discussing loose heavy
objects (which rotate with the earth as well), he repeats the “sympathetic”
explanation alone (p. 22, line 31) “Since the objects which are depressed by
their weight are mainly earthen, there is no doubt that the parts retain the
same nature as their whole (eandem servent partes naturam quam suum totum).”
It becomes perfectly clear that
in the opinion of Copernicus, “equality of nature” is the point that matters in
the whole argument when he discusses flames: they participate in the rotation
(p. 22, 1. 33) “because this fire is earthly and is nourished mainly by earthen
matter.” 4
(4) The teleological, half-animistic conception of
nature appears also in his theory of motion, which is based on the Aristotelian
distinction of “natural” and “artificial” movements. Copernicus explains the falling of bodies
by the Aristotelian theory of “natural place” (locus naturalis, chap. 8,
p. 23, 1. 10). He continues (p. 23,
1. 13 ff.): “Rectilinear movement belongs with objects which wander or
are expelled from their natural places… Nothing is so contrary to the order of
the universe and the form of the world as for a thing to be out of its place
(extra bourn suum… esse). Rectilinear motion, therefore, occurs
only if things are not rightly ordered (rebus non recte se
habentibus).” Obviously Copernicus fully
accepts the
4. It may be mentioned that the medical prescriptions of
Copernicus also - he was for a time physician in ordinary to his uncle, the
bishop of Ermiand - show an entirely medieval spirit. For examples cf. M. Curtze,
Inedita Coppernicana,
115
theory of Aristotle and classical astronomy
5 that
celestial bodies move in circles and that this movement is something “natural,”
whereas rectilinear motion belongs only to terrestrial bodies and is
“artificial,” as it were.
The medieval idea that everything natural is endowed
with an, as it were, spiritual power which is lacking in artificial and
imperfect objects and processes leads Copernicus to a discussion of centrifugal
force which contradicts modern mechanics in a remarkable degree. Already Ptolemy had objected to the
rotation of the earth that by it all objects would have to be thrown off the
earth. 6 Copernicus has to defend his theory against this
objection. He does it as follows
(chap. 8, p. 21, 1. 5): “Things governed by nature produce effects contrary to
those governed by violence. Things
upon which force and impetus are conferred must dissolve and they cannot subsist
for a long time; but what is done by nature is rightly ordered (recte se
habent) and is preserved in its best composition. Ptolemy, therefore, is wrong in fearing
lest the earth and all terrestrial things might be dispersed in a rotation
brought about by the efficacy of nature. This is something quite different from
art or what human ingenuity can carry on.” Obviously Copernicus thinks centrifugal
force appears only in “artificial” not in “natural”
rotation.
The modern answer to Ptolemy’s objection, the argument
that the effects of centrifugal force may be neglected compared with gravity,
would not have been entirely out of the way. Copernicus himself uses the analogous
argument against the objection that the revolution of the earth around the sun
must bring about parallactic shiftings of the fixed stars. There he argues quite correctly that
these cannot be observed (with the insufficient instruments of his period, as we
have to add) because of the great distance of the fixed stars (I, chap. 10, p.
30, 1. 24). 7 Certainly positions of stars could already be measured
in antiquity, whereas in the time of Copernicus no way was available of
measuring centrifugal forces and comparing them quantitatively with gravitation.
The lack of methods of measurement
rather often has resulted in metaphysical explanations of physical phenomena.
At any rate the quoted passages may
have shown sufficiently how much Copernicus is imbued with Pythagorean,
Aristotelian, and Scholastic metaphysics.
A correct quantitative theory of centrifugal force was
developed for the first time by Huyghens, one hundred and twenty years after
Copernicus. Galileo, however,
already ninety years after Copernicus, discussed the centrifugal force connected
with the rotation of the earth in an entirely unmeta-
5. Aristotle, De caelo I, 23; Ptolemy, Almagest
III, 3.
6. Almagest I,
7.
7. Copernicus gave the same argument previously in his
Commentariolus: M. Curtze, op. cit., p. 6, Quarta petitio. Translated by Edward Rosen, Three
Copernican Treatises, 1939, p. 58, assumption 4.
physical way. Certainly his explanation
8 is not yet
correct - he thinks the centrifugal force must at any rate be smaller than
gravitation, however fast the earth would rotate, and produces a would-be
geometrical proof of this assertion - but he knows that the centrifugal effects
in question cannot be observed for the reason that they are too small. The idea that “artificial” rotations
behave differently from “natural” ones is not even mentioned by him. This is highly important, for in the last
consequence the entirely non-mechanical distinction between “natural” and
“artificial” movements excludes experimental research on natural objects. Also with Galileo some teleological ideas
still persist, but they form nothing but the general background of his
explanations. He almost always uses
purely mechanical arguments when he proves his single statements and is strongly
opposed to explanations of natural phenomena by means of sympathy and antipathy.
9
Copernicus is interested in the exact formulation of the
mathematical regularities of celestial movements; he is a Pythagorean, and
advances not one real mechanical idea. Galileo, on the other hand, is a
mechanist: in his dialogue on the theory of Copernicus he is so little
interested in the exact details of the planetary movements that he does not even
mention the laws of Kepler. 10
He considers it much more important to
support the basic ideas of Copernicus by new observations, to show that there is
no fundamental difference between celestial phenomena and terrestrial mechanics
and physics, and to refute the pre-mechanical ideas and objections of the
Aristotelians of his period.
The difference between Copernicus and Galileo is not a
difference of individual psychology only, and even less can it be explained by
the mere difference of time. Kepler, who was a contemporary of
Galileo, was, as is generally known, at least as Pythagorean and thought at
least as teleologically as Copernicus. There rather seems to be a difference
between astronomy and mechanics as to their historical evolution and
sociological origins. The very
first astronomers were Babylonian priests and this connection with priesthood
was never quite interrupted; and from antiquity through the Middle Ages up to
the end of the sixteenth century, astronomy belonged to the “liberal” arts, as
contrasted with the “mechanical” ones. This might explain why metaphysical,
Pythagorean and teleological ideas could persist in astronomy until Copernicus
and Kepler. It is scarcely mere
chance that Copernicus starts his work (I, p. 9) with a eulogy of astronomy
“which is the chief of the liberal arts, is most worthy of free men, and rests
upon almost all kinds of mathematics.” And it is not mere chance that, by
enumerating these, Copernicus gives mechanics as the last one. For me-
8. Diabogo sopra i due
massimi sistemi
9. Cf. Dialogo,
Ed. naz., VII, 436, 17 ff.; Discorsi,
Ed. naz., VIII, 116.
10. The dialogue appeared in 1632, Kepler published his laws
in 1609 and 1619.
117
chanics belonged to the “mechanical arts,” to those
which required the use not only of head and tongue, but also of hands, and
therefore were left to lower-class people. It may be that in the modern era the
experimental method and the elimination of teleological and animistic by causal
thinking originated in those ranks of mechanicians and craftsmen. Certainly scientific mechanics and
physics did not appear in modern times before the way of thinking of the
craftsmen was adopted by academically trained scholars of the upper class, as
happened in the period of Galileo. A more extensive inquiry, however, than
could be given in this short note on Copernicus, would be necessary to verify
this sociological explanation.
International Institute of Social
Research
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