This country is headed toward the adoption of the international metric system of weights and measures, as we are reminded when we are informed by interstate highway signs that, for example, it is fifty miles or eighty kilometers to New Haven. This has been a long time coming. James Madison, writing to his friend James Monroe in 1785, observed that “next to the inconvenience of speaking different languages is that of using different and arbitrary weights and measures,” and urged that the United States lead the way in establishing “universal standards in these matters among nations.”

Among our early Presidents, Jefferson too was keenly interested in a rational system of measurement. Having spent five years (from 1784 to 1789) in France, he was well aware of proposals from various Continental savants that a standard unit of length be set up on the basis of some terrestrial distance, and that all other measures of size, volume, and weight be derived from the standard unit, using the decimal sytem for ease of calculation. Decimal coinage, with all amounts of money expressed in percentages or multiples of the dollar, was approved by Congress in 1787, making America the first country to adopt this reasonable system. The customary fondness for miles, yards, feet, inches, pounds, ounces, quarts, and (perhaps especially) pints, however, was too strong in America to allow further rationalization, and Jefferson’s proposals for a metric system of measurement made little headway. But in France, where a violent revolution had cleared the way for radical innovations, the French National Assembly in 1799 gave official sanction to the metric system, organized essentially as we know it today.

Most differences of opinion about how the new system should be arrived at had to do with the definition of the basic unit of measurement, the meter. A favorite approach was to use the length of a pendulum swinging once a second. The trouble with that was that the length varied slightly with latitude—and the French naturally wanted to use a pendulum in France, the British in England, and the Americans in America. In the end the French, borrowing an idea from the Italians, decreed that the meter should be equal to one forty-millionth of the length of a terrestrial meridian—that is, the distance on the earth’s surface from pole to pole. The most sophisticated astronomical and mathematical methods then known were used in taking this measurement, and a splendid platinum rod of precisely the right length was then made and placed under close guard in France. (It turned out, possibly to the disgruntlement of the British, to be 3.37 inches longer than a yard.) The basic unit having been determined, it was an easy matter to apply the decimal system and derive the kilometer, centimeter, liter (a cube with sides one-tenth of a meter), kilogram (the weight of a liter of water), and so forth.

More refined methods of measurement in the 1880’s revealed that