A Mission for a New Age
In 1792, as the French Revolution reshaped society, the French Academy of Sciences began a project to reshape the world of measurement. The goal was to create a universal standard, free from the chaotic and inconsistent units of the old regime. They decided the new unit, the mètre, would be based on the Earth itself: one ten-millionth of the distance from the North Pole to the Equator, measured along the meridian passing through Paris.
To establish this length, two astronomers, Jean-Baptiste Delambre and Pierre Méchain, were commissioned to conduct a massive survey. Over six years, they would precisely measure the arc of the Paris meridian from Dunkirk on the English Channel to Barcelona, Spain. Delambre handled the northern section, while Méchain took the more rugged southern portion. The 2,784-meter summit of Pic du Canigou was an important station in Méchain's network of triangulations. Its height and isolation provided a clear line of sight to other peaks, allowing for the precise angular measurements needed to calculate the arc's length.
Science Under Siege
The expedition was not a quiet scientific pursuit. France was in turmoil and at war with Spain, making Méchain's work in the Pyrenees extremely dangerous. Locals and revolutionary authorities were deeply suspicious of a man on a mountaintop with strange instruments, lighting signal fires at night. Méchain and his team were arrested multiple times, accused of being spies or counter-revolutionaries.
On the summit of Pic du Canigou, they battled political paranoia. They hauled their primary instrument, the Borda repeating circle, to the exposed peak. This innovative device allowed for unprecedented accuracy by averaging hundreds of measurements. Here, they endured brutal weather, including high winds and snowstorms, while waiting for clear conditions to sight the next survey points.
The intense pressure may have contributed to a small observational error Méchain made at this stage of the survey. The tiny discrepancy, likely only a few arc-seconds, went undiscovered by others but tormented Méchain for the rest of his life. He returned to Spain years later to try and correct his data, but contracted yellow fever and died in 1804. His measurements were so precise that his private anguish had a negligible effect on the final, official length of the meter established in 1799.