The Mapmaker's Wife (4 page)

Christiaan Huygens’s diagram of his pendulum clock.

By permission of the British Library
.

With the king’s blessing, Colbert extended his recruitment efforts beyond France. In an age when European monarchs were constantly waging war, fighting over distant territories and trade routes, Colbert boldly made the French Academy of Sciences an international group, recruiting astronomers, mathematicians, and geographers from Germany, Italy, and Holland. He hired Huygens, a Dutchman, to help direct it and gave him a princely
salary of 6,000 livres. He plucked Italian astronomer Gian Domenico Cassini, whose fame rested on his study of Jupiter’s moons, away from the University of Bologna with a similarly rich offer. Cassini moved his family into a grand observatory that the academy was building outside Paris, an arrangement that so pleased him he changed his name to Jean-Dominique Cassini in honor of his adopted country.

The academy made drawing an accurate map of France its first priority. To begin this task, the academy asked French astronomer Jean Picard to newly determine the earth’s circumference. Picard used varnished wooden rods to carefully stake out a seven-mile baseline between Paris and Fontainebleau, and he employed a quadrant equipped with two telescopes to lay out a precise grid of thirteen triangles from Paris to Amiens. He utilized both solar and celestial observations to determine the latitudes of the endpoints on his north-south meridian, and after two years of painstaking labor, he reported that a degree of arc was 57,060
toises
(a French unit of measurement), or 69.1 miles.

Galileo’s idea of using Jupiter’s moons as a celestial timepiece to determine the longitude of various places could now be put to the
test. This effort was led by Cassini, and after nearly a decade of work, the academy unveiled a startling new map of France. Some cities had moved more than 100 miles, and the country’s coastline had shifted 1.5 degrees closer to Paris. Along its southern border, the coastline had jumped thirty-five miles to the north. France had noticeably shrunk, prompting King Louis XIV, upon being shown the map on May 1, 1682, to lament that the academy’s work
“has cost me a major portion of my realm.”

Jean Picard’s measurement of a degree of latitude.

By permission of the British Library
.

First France, then the world. Data began pouring into the Paris observatory from astronomers throughout Europe, who utilized Cassini’s tables of Jupiter’s moons and newly made pendulum clocks to make their observations. Jesuit missionaries fanning out to the Far East were outfitted with instruments and trained by the academy so that they too could send in longitude and latitude data. Cassini turned all this information into a huge world map, twenty-four feet in diameter, that mesmerized those who saw it. The boundaries between European kingdoms had been redrawn, the Mediterranean coastline had a new shape, and the distant continent of Asia was snapping into focus.

The Paris Observatory.

By permission of the British Library
.

At the turn of the century, Cassini and his son Jacques initiated yet another grand project, one that involved building on Picard’s earlier triangulation work. Picard had measured a distance along a
north-south meridian in the vicinity of Paris. The Cassinis decided that they would extend this triangulation across all of France. By doing so, they would further refine the academy’s measurement of the earth’s circumference, and they would also be able to address a nagging question about the earth’s shape: Was it a perfect sphere?

Ever since Galileo’s time, astronomers focusing their telescopes on Jupiter had noticed that it was flattened at the poles. That observation led to speculation that perhaps the earth was similarly shaped, and then reports began coming into the academy about the strange behavior of the pendulum clock at diverse locations. In 1672, the academy had sent Jean Richer to Cayenne, on the northern coast of South America, where he had found that a pendulum clock that was accurate in Paris lost two minutes, twenty-eight seconds each day. In order to make the clock keep accurate time in Cayenne, Richer had needed to shorten the pendulum by one-twelfth of an inch. Although gravity was not yet understood, Richer’s experiment indicated that its force was not equal at all points on the globe, suggesting that something was indeed amiss with the earth’s shape. And if the earth was not a perfect sphere, then the length of one degree of latitude—as one moved north or south along a meridian line—should change ever so slightly.

The Cassinis began their work in the south of France, where they found a degree of arc to be 57,097 toises (69.2 miles). This was thirty-seven toises—237 feet—longer than Picard’s arc in Paris. Although far from conclusive,
“the success of this work gave us room to conjecture that the degrees of the meridian increase as they approach the equator; whence it results that the earth is prolonged toward the poles,” Jacques Cassini wrote. Over the next eighteen years, the academy extended its triangulation across eight degrees of latitude, a distance of more than 550 miles. This work proceeded fitfully, interrupted by the War of the Spanish Succession and Jean Cassini’s death in 1712, but it produced data consistent with the first observations made in the south. A degree of arc in the north of France was only 56,960 toises, nearly 140 toises shorter than an arc in the southern part of the country. Each degree of latitude apparently
increased by fifteen toises or so as one moved toward the equator, and the conclusion to be drawn from this was clear. The earth, Jacques Cassini flatly declared in a 1718 presentation to the academy, was a “prolate spheroid”—elongated at the poles and cinched in at the equator.
^*

Cassini’s speech marked a triumphant end to a fifty-year effort. France had been mapped, the world had become better known, and the subtleties of the earth’s shape had been revealed. This was an achievement that gave Jacques Cassini and the academy reason to be proud.
“Nothing in our research appears more dignified than to find out the size and shape of the earth, and nothing seems quite as difficult an undertaking,” Cassini wrote. The knowledge that had at last been gained would contribute to “the perfection of Geography and Navigation, sciences that are most useful to society.”

There was only one fly in this sea of French pride: Isaac Newton.

I
NVESTIGATIONS INTO THE EARTH
’
S
size and shape invariably raised questions about the physical forces that governed the universe. The great conceptual leap of the Greeks in the sixth century
B.C
. was not just recognizing that the earth was a globe but coming to believe that it was a globe freely floating in space. Nicholas Copernicus’s declaration in 1543 that the earth and other planets orbited around the sun, while seen by the Catholic church as the worst sort of heresy, set the great minds of Europe to pondering how this could be: What kept the planets in their orbits? In 1609, German astronomer Johannes Kepler, observing that planets traveled about the sun in elliptical orbits, speculated that the sun
“emits from itself through the extent of the Universe” an attractive power that held the planets in its grasp. Kepler theorized that the sun sent out straight lines of force, like spokes on a wheel, and that as the sun rotated on its axis, these lines of force pushed the planets along.

Religious persecution prevented Galileo from directly addressing this question, but he still managed to make his thoughts known. In 1633, he was forced by the Inquisition in Rome, upon threat of torture, to recant the Copernican doctrine. Afterward, he did not dare write openly about planetary orbits. However, in his 1638 book
Discourses on Two Sciences
, he described how a body in motion travels in a straight line unless a force acts upon it and changes its course. Alert readers understood the implication: The earth and other planets would fly off into space unless there was a force—presumably emitted by the sun—that caused them to travel along curved paths.

The greatest French thinker of this period was Descartes, who applied the philosophy he articulated in
Discourse on Method
to the movement of planets. God, he reasoned, had set the universe in motion, much as one might wind up a clock. But once in motion, the universe operated according to a mechanistic design. Descartes reasoned that space could not exist without material, and thus even if it were empty of heavier matter, like water or air, it remained filled with invisible particles. In essence, space was to be seen as a fluid-filled medium; thus fluid dynamics could explain the forces of the universe. Descartes theorized that streams of particles swirled around the sun like water in a whirlpool, carrying along the planets, with the rings of particles nearest the sun swirling the fastest. The reason that the swirling particles did not fly away from the sun in a straight line was that there were similar vortices around all the other stars, each great vortex crowding into the next, and it was this pressure from the other stars’ vortices that kept the system in balance.

Descartes set forth his cosmology in
Principles of Philosophy
, published in 1644. Although religious authorities in France did not react well to it—his writings were placed on the country’s Index of Prohibited Books in 1663—the members of the French Academy of Sciences did. Descartes had provided a mechanistic explanation for the workings of the universe, and in
Principles of Philosophy
, he had even explained how a fluid-filled space transmitted light. It all made
sense, and it was a worldview that guided the academy members in their own 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.