The Mapmaker's Wife Read Online Free PDF Page A

investigations into the nature of the universe. Huygens, for instance, applied Cartesian physics to the problem of gravity, writing that the rotating ether thrusts those standing on the surface of the earth toward its center. In 1686, the academy’s secretary, Bernard Le Bovier de Fontenelle, published a popular book on astronomy titled Entretiens sur la pluralité des mondes that was essentially a primer on Cartesian physics, and it not only survived the king’s censorship but became a best-seller. Descartes and his swirling vortices were one of the crowning achievements of seventeenth-century French science.

    The Cartesian vortices. The circle in the center of each vortex represents a sun.
    From René Descartes , Principles of Philosophy (1644). Edgar Fahs Smith Collection, University of Pennsylvania Library
    Across the English Channel, Sir Isaac Newton was in partial agreement with Descartes: He too believed that science should search for a mechanical explanation of the universe. However, his inquiries and mathematical brilliance led him to a different model, one that followed Kepler’s notion of “attraction at a distance.” By his twenty-fourth birthday, in 1666, Newton had deduced a mathematical formula for gravity. The attraction between two bodies, he concluded, is directly proportional to the product of their masses and indirectly proportional to the square of the distance between their centers. Thus the tug of gravity at the earth’s surface is sixty-four times stronger than it is at a place eight times further from the earth’s center. However, when Newton applied his theory to the moon’s movements, the numbers did not quite add up. At that time, English sea charts—whose authors were apparently unaware of the arc measurements made by Snell and Norwood fifty years earlier—stated that one degree of latitude was only sixty miles, and if that were so, the earth was too small to exert a sufficient gravitational pull to keep the moon in its orbit. This led the baffled Newton, a historian later wrote,“to entertain a notion that together with the force of gravity there might be a mixture of that force which the moon would have if it was carried along in a vortex.” In other words, perhaps Descartes was partly right.
    Newton’s doubts about his theory of gravity disappeared in 1682 after he came upon Picard’s updated estimate for the size of the earth. Once he plugged in 24,714 miles for the earth’s circumference, his formula for gravity worked almost perfectly.“How these Attractions (between bodies) may be perform’d, I do not here consider,” he wrote in his masterpiece, Principia . “What I call Attraction may be perform’d by impulse, or by some other means unknown to me. I use that Word here to signify only in general any force by which bodies tend towards one another, whatsoever be the Cause.”
    In Principia , Newton specifically attacked Descartes’s vortex theory, pointing the French to their own experiments as proof that Descartes was wrong. The fact that Richer’s pendulum clock beat slower in Cayenne was evidence that gravitational pull at the equatorwas less than it was in Paris, which in turn was evidence that the earth bulged at the equator—the clock was further away from the earth’s center. And the reason the earth bulged at the equator was because it rotated on its axis, which created a stronger centrifugal force at the equator than at the poles. * The same physics, Newton argued, had turned Jupiter into a similar oblate shape. In Book III of Principia , Newton summed up his challenge to French beliefs, proclaiming—as Proposition 18, Theorem 16—that“the axes of the planets are less than the diameters drawn perpendicular to the axes.” By his calculation, this ratio of axis to diameter should be 229 to 230.
    At first, Newton’s work did not cause much of a stir in France. England and France were constantly at war during this period, which diminished the exchange of