Used with
permission of Maiken Naylor, University at Buffalo, Buffalo, NY, USA,
http://ublib.buffalo.edu/libraries/units/sel/exhibits/stamps
A joint issue of France and Finland commemorates simultaneous 1736 French expeditions to the equator in South America and the polar regions of Lapland to determine the shape of the earth, generally acknowledged to be spherical. Charles LaCondamine (1701-1774) in Peru and Pierre Maupertuis (1698-1759) in Lapland surveyed the curvature of the meridians and found that the earth was somewhat flattened at the pole, and more curved at the equator, giving it the shape of an oblate spheroid.
This confirmed Newton's theory put forth in the Principia that the centrifugal force of the rotating earth caused it to be distended at the equator, where the speed of rotation was greatest, and flattened at the poles, where the speed was zero - as indicated on the Finnish stamp. Anders Celsius (1701-1744), the Swedish
astronomer, was also a member of the northern expedition. He
was the inventor of the centigrade thermometer, which divides
the range in temperature between the freezing and boiling points
of water into 100 degrees. These divisions are now called degrees
Celsius.