Scott Benoit, age 11, of Utica, N.Y., for his question:   

WHEN DID THE METRIC SYSTEM BEGIN?

The metric system was invented in France almost two centuries ago. Since that time, other countries gave up their sloppy measuring systems and adopted Systeme International d'Unites. The streamlined name for this International System of Units is simply SI.

Actually the complete story comes in two parts. The first chapter began in Neolithic days, when people started hefting and comparing weights and pacing off distances. These people of the New Stone Age gave up roaming and hunting in favor of settled communities. They invented measuring units to cope with building, farming and trading. Different communities invented different units, and none of them was very precise.

Now and then a ruling monarch tried to establish set units throughout his domain.  Often extra units were added by conquerors and visiting traders. Through the centuries, the worldwide measuring systems became a mish mash, with each country using its own units. This part of the story ended in the 1600s, when several thoughtful people decided that a reformed system, usable by all, was way overdue.

One practical solution was suggested in 1670 by Gabriel Mouton, the vicar of a church in Lyons, France. His sound idea was to base an entire measuring system on a natural unit which could not be disputed. He suggested a unit of length equal to one 21,600th part of the earth's circumference. In the language of arcs and circles, this distance is called one minute.

The next year, 1671, a French astronomer named Jean Picard used the laws of motion to fix on a basic unit. His standard‑length unit was based on the one‑second swing of a pendulum. These and several ideas failed to get very far, but they did get people thinking about the need for a simplified, unified system for weights and measures.

    In 1790, the French government asked its Academy of Sciences to solve the problem in detail. A commission of experts worked out a complete system of weights and measures based on the meter‑length unit and using the decimal system of tens.    

The French government approved this in 1795‑‑but it was not adopted by the French people until 1840.  Since then the basic system has been refined and improved. By 1850, it was adopted by Holland, Spain, Italy and Greece. In the next 50 years, 45 more countries joined up. Others joined the metric nations one by one. Now Canada and Australia are changing‑‑and the only major non-metric country is the United States.