Barely two centuries after Columbus found that the world wasn’t flat, scientists set out to establish whether it was really round. The question required comparing the distance between degrees of latitude in Europe — which had been measured — with that distance in the Arctic or at the equator.
In his latest book, Ferreiro gives life to three French scientists and their 1736 geodesic mission to the equator. Astronomer Louis Godin, mathematician Pierre Bouguer and geographer Charles Marie de La Condamine offer a snapshot of another time.
The scientists traveled to a plateau near Quito in South America. There they surveyed a 215-mile line and used it to calculate giant imaginary triangles using geometry, trigonometry, a device called a quadrant, star sightings and land distance measurements. Triangulating nearby peaks of the Andes with points on the ground, they found that one degree of latitude was shorter at the equator than in Europe. In other words, the Earth bulges at the equator.
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At times the story can bog down in detail, but surprises make up for it. The mission was the first large international scientific expedition attempted and led to the discoveries of rubber and cinchona bark — the source of quinine — and the naming of Ecuador.
Not until 1743, after the calculations were complete, did the scientists realize they had also determined Earth’s size. La Condamine found out belatedly; he was on the first scientific expedition down the Amazon. Another time indeed.
Basic Books, 2011, 337 p., $28