The long road to the metre
Before the metric system, a foot or a pound could mean something different in every town. Fixing that took a revolution.
Imagine buying cloth in one town and being told it measures a certain length, then going to the next town and finding that the same word means something else. That was normal in much of Europe for centuries.
A tangle of units#
Every region had its own units. A pound, a foot or a bushel might vary from place to place, and often depending on what was being measured. This caused confusion in trade and room for cheating.
Reformers wanted something clear, shared and based on nature.
The French idea#
During the French Revolution in the 1790s, scientists proposed a new system, built on measures that anyone could in principle reproduce. The unit of length, the metre, would be defined as one ten-millionth of the distance from the North Pole to the equator along a meridian passing through Paris.
Two astronomers, Jean-Baptiste Delambre and Pierre Méchain, spent years surveying the distance between Dunkirk and Barcelona to work it out. The work was slow and dangerous, with war and politics in the way.
Everything in tens#
The new system was decimal. Smaller and larger units were made by multiplying or dividing by ten, so there was no need to remember how many ounces were in a pound. Names used prefixes such as kilo, centi and milli.
In 1799, platinum standards for the metre and the kilogram were deposited in the French archives.
Slow adoption#
People did not switch at once. France itself went back to older units for a while, and the system only became firmly established there later. Gradually, other countries adopted it. In 1875, an international treaty set up a body to look after the standards, and the system became the basis of the modern International System of Units.
Where we are now#
Most of the world uses metric units today. The metre is now defined from the speed of light rather than a piece of platinum or the shape of the Earth, but the idea is the same: a shared standard that anyone can check.
A good measure is one everyone agrees on. That sounds simple and took a revolution.