METRIC SYSTEM OF WEIGHTS AND MEASURES. 175 



of the system, so clear and simple that a child can under- 

 stand it: 



The Metric System of weights and measures is formed 

 upon the decimal scale, and has for its base an invariable 

 unit derived from nature, and called a METRE ; and upon 

 this unit all the units of weight and measure are based. 



The Metre is the ten-millionth part of the distance from 

 the equator to the pole ; and is the principal unit of linear 

 measure. 



Are is a square whose side is ten metres. It is the 

 principal unit of superficial measure. 



The Stere is a cube whose edge is a metre. It is the prin- 

 cipal unit of solid or cubic measure. 



Tfie Litre is a cube whose edge is the tenth of a metre. 

 It is the principal unit of all measures of capacity. 



The Gram is the weight of a cube of pure water at its 

 greatest density, whose edge is the hundredth part of a 

 metre. A litre of water weighs 1,000 grams. It is the prin- 

 cipal unit of weight. 



The names of the derivative denominations are formed 

 by joining a Latin or Greek prefix to the principal units. 

 There are seven of these prefixes, derived as follows : 



( MILLI, from MilUsimus, a thousandth. 

 Latin. < CENTI, from Centesimus, a hundredth. 

 ( DECI, from Decimu-s, a tenth. 



