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Section 6: Motive Forces and the Stars
As the sun-centered system gained acceptance, the role of the stars in moving the planets ended. Without the mechanism of the spheres, other sources of motion had to be found that kept the planets in their orbits. Some returned to Plato, who thought the celestial bodies were besouled and could move themselves. Others called for angels to move the planets, evoking Aristotle's requirement for eternal planetary movers in his Metaphysics. A more efficient suggestion was God's commandment to move them by fiat.
William Gilbert offered magnetism as the motive force in 1600, which Kepler assigned to the sun, attracting the planets' orbits around it. While the sun-centered system required these new forces, Descartes' source of motion required a new universal model. His theory of vortices described a fluid medium in the universe that carried the planets around our sun, and the planets of other stars around theirs. The stars, far from acting as an eternal and unchanging source of motion, were dispersed, and were acted upon by the fluid medium.

An Illustration of Genesis with quote from Psalms at the top reads "By the word of the Lord were the heavens made, their starry host by the breath of his mouth." from Johann Zahn,Specula Physico-Mathematico-Historica Notabilium ac Mirabilium Sciendorum,1695.

Above, left to right:
* In Johann Kepler's 1609 Astronomia Nova seu Physica Coelestis, the magnetism of the sun affecting the motion of Mars is compared to rowing a tethered boat in a river.

* René Descartes' Principia Philosophiae, 1656, shows our sun [at S] as one of many other solar systems [L,C,K,O] in the cycling vortices.

Linda Hall Library of Science, Engineering & Technology
5109 Cherry Street, Kansas City, MO 64110
This exhibition is made possible by generous support from Mr. & Mrs. James B. Hebenstreit and Mrs. Lathrop M. Gates.