Friday 15 May 2015

A Short History of Nearly Everything: Measuring a Meridian

"If you had to select the least convivial scientific field trip of all time, you could certainly do worse than the French royal Academy of Sciences' Peruvian expedition of 1735.   Led by a hydrologist named Pierre Bouguer and a soldier-mathematician named Charles Marie de la Condamine, it was a party of scientists and andvetures and who travelled to Peru with the purpose of triangulating distances through the Andes.

At the time people had lately become infected with a powerful desire to understand the Earth - to determine how old it was, and how massive, where it hung in space, and how it had come to be.   The French party's goal was to help settle the question of the circumference of the planet by measuring the length of one degree of meridian (or one-360th of the distance around the planet) along a line reaching from Yarouqui, near Quito, to just beyond Cuenca in what is now Ecuador, a distance of about 320 kilometres.

Almost at once things began to go wrong, sometimes spectacularly so.   In Quito, the visitors somehow provoked the locals and were chased out of town by a mob armed with stones.   Soon after the expedition's doctor was murdered in a misunderstanding over a woman.   The botanist became derranged.   Otheres died of fevers and falls.   The third most senior member of the party, a man named Jean Godin, ran off with a thirteen-year-old girl and could not be induced to return.

At one point the group had to suspend work for eight months while La Condamine rode off to Lima to sort out a problem with their permits.   Eventually he and Bouguer stopped speaking and refused to work together.   Everywhere the dwindling party went it was met with the deepest suspicions from officals who found it difficult to believe that a group of French scientists would travel halfway around the world to measure the world.   That made no sense at all.  Two and a half centuries later, it still seems a reasonable question.   Why didn't the French make their measurements in France and save themselves the all the bother and discomfort of their Andean adventures?

The answer lies partly with the fact that eighteenth century scientists, the French in particular, seldom did things simply if an absurdly demanding alternative was available, and partly with a practical problem problem that had arisen with the English astronomer Edmond Halley many years before - long before Bouguer and la Condamine dreamed of going to South America, much less had a reason for doing so.

(...)

They chose the Andes because they needed to measure near the equator, to determine if there really was a difference in sphericity there, and because they reasoned that mountains would give them good sightlines.   In fact, the mountains of Peru were so contantly lost in coud that the team often had to wait weeks for an hour's clear surverying.   On top of that, they had selected one of the most nearly impossible terrains on Earth.   Peruvians refer to their landscape as muy accidentado - "much accidented" - and this it most certainly is.   Not only did the French have to scale some of the world's most challenging mountains - mountains that defeated even their mules - but to reach the mountains they had to ford wild rivers, hack their way through jungles, and cross miles of high, stony, desert, nearly all of it uncharted and far from any source of suppplies.   But Bouguer and La Condamine were nothing if not tenacious, and they stuck to the task for nine and a half long, grim, sun-blistered years.   Shortly before concluding the project, word reached them that a second French team, taking measurements in northern Scandinavia (and facing notable discomforts of their own, from squelching bogs to dangerous ice floes), had found that a degree was in fact longer near the poles, as Newton had promised.   The Earth was 43 kilometres stouter when measured equatorially than when measured from top to bottom around the poles.

Bouguer and La Condamine thus had spent nearly a decade working towards a result they didn't wish to find only to learn now that they weren't even the first to find it.   Listlessly they completed their survery, which confirmed that the first French team was correct.   Then, still not speaking, they returned to the coast and took separate ships home."

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