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ON THE SHELFTropical Math Quest

Scientist-explorers faced danger and hardship in pursuit of precision.

MEASURE OF THE EARTH: The Enlightenment Expedition that Reshaped our World

by Larrie D. Ferreiro.
Basic Books 2011, 376 pages.

Over the next few months, as engineers make final adjustments in the construction of a new airport just outside Quito, Ecuador, they’ll be working along the same long, flat plain that once supported an even more ambitious project: establishment of a geodesic baseline to help determine the shape of the Earth.

Undertaken by a joint French-Spanish team, the 1735 Geodesic Mission was a large-scale scientific endeavor unlike any previously attempted. Its success marked a watershed of Enlightenment scientific inquiry and inspired in subsequent decades innumerable projects in navigation, astronomy, and botany. In Measure of the Earth, author Larrie Ferreiro transports readers to an intriguing world of colonial politics and scientific competition, blundering incompetence, dedication, and hardship. In doing so, he reconstructs a story of early scientific exploration that will surely interest Prism readers.

The debate that prompted the 1735 mission was championed on one side by French philosopher René Descartes, who believed that Earth was an elongated sphere, shaped like an egg; and on the other, by English mathematician Isaac Newton, who championed an oblate shape—Earth as a squashed sphere. European governments grew interested because of the implications for ocean navigation and political advantage: “the nation that could accurately locate its ships at sea could control an empire.”

Urged on by its Navy minister, the French government sponsored the mission, which would take three French scientists, two Spaniards, and a host of assistants—a botanist, surgeon, cartographer, draftsman, and instrument maker—to the Spanish Viceroyalty of Peru. The goal was to determine the length of a degree of latitude at the equator, which could then be compared with measurements taken in Paris, helping to finally settle the issue of “the figure of the Earth.”

As an engineering educator and naval architect, Ferreiro demonstrates mastery of the technical concepts and ease in translating them for the general reader. Yet the real pleasure of this book lies in the nuanced portraits of the mission’s three French scientists: project leader Louis Godin, who quickly burned through group funds on gifts for a favorite prostitute; wealthy, socially adept Charles-Marie de La Condamine, whose breezy trip report, Journal of the Voyage to the Equator, would help popularize both scientific endeavors and South America; and astronomer Pierre Bouguer, who joined the mission only reluctantly but eventually produced its most solid work and leadership.

The three had “prepared for their journey as scientists, not as explorers,” Ferreiro tells us, “and this would nearly be their undoing.” Staggered by the oceanic journey and months of difficult overland travel merely to reach Quito, the scientists quarreled and split into different camps. In the first twelve months, they spent the equivalent of a quarter million dollars, leaving themselves impoverished for much of the remaining nine years it would take to complete the mission. The savvy La Condamine found refuge in a Jesuit seminary, where he hocked his lavish personal goods: silks, linens, diamond and emerald jewelry, and a set of silver and gold spoons.

Despite continued setbacks, disagreements, bouts of malaria, and the violent death of their surgeon in an honor duel, the mission members pressed on. Over a period of seven years, trekking into the Peruvian jungles and up high mountains, they constructed a precise seven-mile-long straight path containing a series of pyramids for focal point-measurements and astronomical calculations. Measuring the angle of the star Epsilon Orion from either end of the pyramid chain was their final task, one that required building an eighteen-foot zenith vector, then three months of long nights under the stars, taking notes, waiting for the right weather conditions, and “adjusting and readjusting” their instruments.

In the end, the mission achieved its single, crucial number: 68.7 miles for the length of a degree of latitude at the equator. The accuracy of the measurement—within 50 yards of the currently accepted value—is breathtaking, writes Ferreiro, “even by today’s standard.” And it vindicated Newton, defining the shape of the Earth as an oblate spheroid.


Robin Tatu is a contributing editor of Prism.




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