In 1791 the French nation， in the midst of a revolution， wished to break with the past， especially with those aspects of it which they considered illogical and useless. One of these was the traditional system of weights and measures then in use. Not only was the system overly complicated， but it also varied widely from place to place.
In constructing the new system， the French began by setting up a unit of distance equal to one forty millionth part of the earth’s circumference①. Unfortunately， later measurements showed that the unit designated② was not exactly that fraction， but they continued to use it.（Today the unit is defined simply as the distance between two marks on a platinum③-iridium④ bar kept in a suburb of Paris.） The unit is the meter， and the system of measurements based on this unit is the metric system， the system today used by scientists the world over.
The metric system is built in units of ten， Greek prefixes⑤ showing multiples and Latin prefixes showing fractions⑥. The Greeks had no word for a number larger than ten thousand and the Romans had none for a number larger than one thousand， but the system was extended by using less specific words； for instance megameter（one million meters）is derived from a Greek word that means simply “large”.
① circumferencen. 圆周；周长[C][U]
② designatev. 标出；表明；指定
③ platinumn. 铂，白金[U]
④ iridiumn.［化］铱
⑤ prefixn. ［语］字首，前缀
⑥ fractionn. 小部分；片段；碎片
当今世界上使用的米制
1791年，处于一场革命中的法国民族，希望与过去决裂，特别是与其中他们认为不合逻辑、没有用处的那些东西决裂。其中之一便是当时使用的度量衡制，它不仅过于复杂，而且在这一处与那一处迥然不同。
在建设新制中，法国人创立了一个相当于地球圆周线4，000万分之一长的距离单位。不幸的是，后来进行的测定表明，所规定的这一单位并不精确地符合这一分数。但是，法国人继续沿用它。（今天，这一单位仅仅是保存在巴黎郊区的一根铂铱杆上两个刻度间距的定义。）这个单位便是米，以这一单位为基础的测量制便是米制——全世界科学家们今天所使用的测量制。
米制是以10进制单位建立起来的，希腊文前缀表示倍数，拉丁文前缀表示分数。希腊人没有字表示大于1万的数，罗马人也没有字表示大于1，000的数。然而，这一测量制却能用较不专门的词延伸开来，例如：megameter（100万米）就是出自一个希腊字，这个字只不过是“大”的意思。
