What Did Isaac Newton Discover

How did we discover the Earth wasn't round?

Jonathan Beard, contributor

(Image: W. ROBERT MOORE/National Geographic Stock)

In Measure of the Earth , Larrie Ferreiro recounts the fascinating tale of an equatorial expedition to determine the shape of the planet

IN 1671, France sent astronomer Jean Richer to South America to map the skies of the southern hemisphere. Richer, whose work helped the French navy navigate the world, took with him two pendulum clocks. Though they had been carefully calibrated in Paris, he was dismayed to find that they lost 2 minutes 28 seconds per day in French Guyana compared with local clocks.

Upon his return home in 1673, this discrepancy caused an international scientific uproar. Isaac Newton declared that the clocks beat more slowly near the equator because the force of gravity was less there, and that gravity was less because the planet bulged at its waist due to the centrifugal force generated by its rotation. French scientists rejected Newton's oblate Earth, maintaining instead that the planet is pointed, rather than flattened, toward the poles.

Both sides realised that measuring the length of a degree of latitude at various points - especially near the equator and poles - would reveal the true shape of the Earth. An expedition needed to be sent to the equator to survey a line, as nearly north-south as possible, hundreds of kilometres long. With Africa considered impenetrable and Asian equatorial sites very far away, Spanish America beckoned.

In 1733 a Franco-Spanish team of scientists, naval officers, device-makers and servants was assembled. In Measure of the Earth , Larrie Ferreiro tells the story of their adventures. They set sail in 1735, expecting to spend three or four years taking measurements in the viceroyalty of Peru. Instead, it would be nine years before any of them would see Europe again, and several would never make it. Their surgeon died by the sword, the youngest succumbed to malaria, while two were marooned in the New World for lack of money.

The team did measure the surface distance of one degree of latitude in what is now Ecuador. They found it to be 56,753 toises (a French unit of measurement at the time) - just 50 metres off today's value - proving Newton right. Ironically, by the time they reached Paris, another French team had gone north to the Arctic circle and taken measurements confirming the Earth to be oblate, ending the debate.

Unlike past seafaring and polar ventures, these geodetic expeditions are now almost forgotten. Although Ferreiro explains their scientific work, his main interest is the human story, very much warts-and-all. Expedition members quarrelled, overspent their budgets, and one leader abandoned two daughters in Peru. The team came prepared for steamy jungles, but suffered more from altitude sickness and cold. And perhaps most tellingly, these Europeans scarcely noticed the indigenous people who cooked their food and carried their burdens.

Robert Hooke discovered the Inverse Square Law, not Isaac Newton ...

This fact is clearly record in “Brief Lives” by John Aubrey, F.R.S.: “Mr Hooke wrote to Mr Isaac Newton of Trinity College Cambridge……. Mr Hooke sent, in his next letters, the whole of his hypothesis, that is, that the gravitation was reciprocal to the square of the distance”. However Newton was the one who greatly developed the original idea by Robert Hooke, of Christ Church College Oxford, but Newton did not acknowledge Hooke. This is the cause of the well known friction between these two scientists. Newton originally thought that the force (as we now call it) was inversely proportional to distance, not square of distance. John Aubrey discovered the Aubrey holes of Stonehenge and was the great grandson of Dr William Aubrey, Fellow of All Souls Oxford, kinsman of Henry Herbert, 2nd Earl of Pembroke, and kinsman of Dr John Dee, and associated with the Yale family. They were descended from my own ancestor and that of the Morgan / Aubrey Family of Glyn Tawe: Jenkin ap Morgan Aubrey of Abercynfrig, who was descended from Prince Bleddyn ap Maenarch. John Aubrey F. R. S. has short autobiographies (“Brief Lives”) of many famous scientists, including : Isaac Barrow (who gave up his Chair for Isaac Newton), Boyle, Descartes, Halley, Hobbes, Hooke, Mercator and Wren.

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