Triangulating the Meridian

Two Men’s Quest for the Meter Through War and Revolution

The Astronomers and the King

• On June 19, 1791, the French Revolution was about to begin

• King Louis XVI met with two astronomers, members of the Academy of Sciences

• The King authorized a huge undertaking: measure the Earth in order to standardize the length of the meter

Jean-Dominique, comte de Cassini

King Louis XVI of France

Pierre Mechain

The Palais des Tuileries

Measurements Varied

• The volume of a “standard” bushel of corn was controlled by each local community

• The standard units of length, weight, and volume might change to compensate for bad times, such as decreasing the amount of bread in each loaf

• This is called a “Just Price” economy• It was confusing and could be unfairly

manipulated

Enter the Savants

• Many savants (scientists or other learned people) and legislators wanted a standard

• In 1789, the nobility renounced all their legal privileges, leading they way to new laws governing measures

• The Paris Academy of Scientists designed the new system

Natural Measures

• During the French Revolution people wanted the new measures to be natural, not based on antiquated notions

• Between 1793 and 1795 France adopted a ten hour day by decree, although it was rarely used

• They tried to mandate angle measurements in 400 grads per circle (instead of 360º) but mostly failed

The Meter Controls Them All

• One liter is one thousand cubic centimeters

• One gram is the weight of one cubic centimeter of water

The Meridian• One meter is supposed

to be one ten millionth of the distance from the equator to the pole

• The savants needed to accurately measure the size of the earth over a long distance

• They chose Dunkirk to Barcelona

Triangulation• If you know the

angles of two triangles and one side, you can find the other sides

• The astronomers used special instruments to sight from one vertex to another

Solving Triangles

• To find missing sides of general triangles, use the Law of Sines and the Law of Cosines

• Actual surveying must account for height also

Revolution and Adventure!

• Two expeditions set out, one north and the other south

• Several times they skirted war zones

• They were captured by the Spanish army and the Italian navy

• They climbed steep hills to windswept lookout towers that marked each vertex

CreditsImages:

Cassini - http://en.wikipedia.org/wiki/File:Jean_%28Jacques%29_Dominique_de_Cassini.jpg,Mechain - http://commons.wikimedia.org/wiki/File:Pierre_mechain.jpgLouis XVI - http://www.educatorunderground.com/bios/Louis%20XVI.htmlThe Palais des Tuileries - http://saint-sevin.pagesperso-orange.fr/pageg.htmMerdian map and triangulation map from The Measure of All Things, Ken Adler, 2002