The Magazine

Heaven and Earth

Their conflict and harmony in the life of Galileo.

Jan 31, 2011, Vol. 16, No. 19 • By DAVID GUASPARI
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Galileo
by John Heilbron
Oxford, 528 pp., $34.95

Heaven and Earth

Galileo

Time-Life Pictures / Getty

Galileo
Watcher of the Skies
by David Wootton
Yale, 354 pp., $35

In 1610, Galileo published The Starry Messenger, a brief report of wonders seen through his state‑of‑the‑art telescope: mountains on the moon, vast multitudes of stars invisible to the naked eye, moons circling Jupiter, earthshine (the illumination of our moon by sunlight reflected from Earth). It promised a future work to refute “those who argue that the earth must be excluded from the dancing whirl of stars” and show that it is “a wandering body surpassing the moon in splendor, and not the sink of all dull refuse of the universe.”

Earth was a “sink of all dull refuse” according to then-dominant Aristotelian cosmology and physics, whereby each of the four elements (earth, water, air, fire) composing terrestrial objects has a proper place and, unless obstructed, proceeds by “natural motion” toward it. The proper place for the element earth is the center of the universe. The coarse and gross objects in which it predominates are heavy because they naturally move toward that center and thereby accumulate on Earth. Bodies composed of these four elements are confined to the region between Earth and the moon​—​the “sublunary sphere”​—​which, since the four can metamorphose into one another, is the domain of change and decay. The sun, moon, planets, and stars​—​which circle Earth in the superlunary heavens​—​are composed of the fifth element, unchanging ether.

The Aristotelian account is consistent with Ptolemy’s geocentric model of the universe, but cannot be reconciled with a scarred and pitted moon, an Earth that shines like a star, or a planet having moons of its own. The Starry Messenger tells us, says David Wootton, that “the earth is a heavenly body and the heavens contain earthly bodies.”  The 400th anniversary of its publication has been the occasion for two substantial biographies of Galileo, both scholarly but accessible to the general reader.

John Heilbron depicts a Renaissance humanist: not only a great scientist but a skilled musician and artist; a polemicist, literary stylist, poet, and playwright; a brilliant debater; a lover of wine. He shows us Galileo’s intellectual and social circles, complicated politico‑theological intrigues, court spectacles intended “to stupefy every viewer with their grandeur,” and the chaos within Galileo’s (at best) semifunctional family. David Wootton provides an intellectual biography concerned primarily with the development of Galileo’s scientific ideas. He gives lucid accounts of the intellectual stakes in Galileo’s scientific controversies and striking interpretations (and reinterpretations) of important historical questions. Scholars will evaluate the book’s novelties; to this nonscholar, most of its pages ranged from absorbing to dazzling.

 A quick example: Galileo’s contemporaries had good reasons to be cautious about astronomical evidence from telescopes. Its reliability could not be directly verified by comparing telescopic images of the heavens with close-up observation by the naked eye; nor could it be inferred from experiments with terrestrial objects​—​since similarity of the celestial and terrestrial realms is precisely the matter in dispute. But, says Wootton, Galileo faced a more radical difficulty because he lived in a culture unlike our own, one in which seeing was not believing. Sight was the most easily deceived of the senses​—​what was perspective drawing but systematic trickery?​—​so why trust it “to provide information on a world [we] would never touch, hear, or smell”?

When The Starry Messenger appeared, Galileo was a 46-year-old mathematics professor at the University of Padua who had published nothing significant. Yet he had by then made all his major discoveries and founded the very notion of an experimental science. How had he thought his way out of the Aristotelian physics and Ptolemaic astronomy of his teachers and mentors? Answers must be conjectural: We lack not only published work but, for some important periods, even notes and papers, and those that survive can be difficult to date.

Galileo dedicated his booklet to the grand duke of Tuscany and became the duke’s official mathematician and philosopher​—​giving up a lifetime position at Padua and the protection that the powerful Republic of Venice would have offered against the Roman Inquisition. Principally, Heilbron and Wootton agree, he wanted access to the Jesuits so that he could convert the intellectual world of Rome to Copernican astronomy.

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