IF YOU HAD to select the least vivial stific field trip of all time, you could certainlydo worse than the French Royal Academy of Sces』 Peruvian expedition of 1735. Led by ahydrologist named Pierre Bouguer and a soldier-mathemati named Charles Marie de Lai arty of stists and adventurers who traveled to Peru with the purposeulating distahrough the Andes.
At the time people had lately bee ied with a powerful desire to uand theEarth—to determine how old it was, and how massive, where it hung in space, and how it hade to be. The French party』s goal was to help settle the question of the circumferehe pla by measuring the length of one degree of meridian (or 1/360 of the distance aroundthe pla) along a line reag from Yarouqui, near Quito, to just beyond what isnow Ecuador, a distance of about two hundred miles.
1Almost at ohings began to g, sometimes spectacularly so. In Quito, the visitorssomehow provoked the locals and were chased out of town by a mob armed with stones. Soohe expedition』s doctor was murdered in a misuanding over a woman. Thebotanist became deranged. Others died of fevers and falls. The third most senior member ofthe party, a man named Pierre Godin, ran off with a thirteen-year-old girl and could not beio return.
At one point the group had to suspend work fht months while La ine rode off toLima to sort out a problem with their permits. Eventually he and Bouguer stopped speakingand refused to work together. Everywhere the dwindling party went it was met with thedeepest suspis from officials who found it difficult to believe that a group of Frenchstists would travel halfway around the world to measure the world. That made no seall. Two and a half turies later it still seems a reasonable question. Why didn』t the Frenchmake their measurements in Frand save themselves all the bother and disfort of theirAndean adventure?
The answer lies partly with the fact that eighteenth-tury stists, the Fren particular,seldom did things simply if an absurdly demanding alternative was available, and partly ractical problem that had first arisen with the English astronomer Edmond Halley manyyears before—long before Bouguer and La ine dreamed of going to South America,much less had a reason for doing so.
* Triangulation, their chosehod, ular teique based on the geometric fact that if you know thelength of one side of a triangle and the angles of two ers, you work out all its other dimensions withoutleaving your chair. Suppose, by way of example, that you and I decided we wished to know how far it is to theMoon. Using triangulation, the first thing we must do is put some distaween us, so lets say fumentthat you stay in Paris and I go to Moscow ah look at the Moon at the same time. Now if you imagine aline eg the three principals of this exercise-that is, you and I and the Moon-it forms a triangle. Measurethe length of the baseliween you and me and the angles of our two ers and the rest be simplycalculated. (Because the interiles of a triangle always add up to 180 degrees, if you know the sum of twoof the angles you instantly calculate the third; and knowing the precise shape of a triangle and the length ofone side tells you the lengths of the other sides.) This was in fact the method use by a Greek astronomer,Hipparchus of Nicaea, in 150 B.C. to work out the Moons distance from Earth. At ground level, the principles ulatiohe same, except that the triangles dont reato space but rather are laid side to side on am