556 EVERYDAY SCIENCE 



Measure of Length. In- the metric system the unit 

 of length is the meter. In the United States it is the dis- 

 tance between two transverse lines on each of two bars of 

 platinum-iridium at the temperature of melting ice. These 

 bars, which are called " national prototypes," were made 

 by an international commission and were selected by lot 

 after two others had been chosen as the " international pro- 

 totypes " for preservation in the international laboratory 

 on neutral ground at Sevres near Paris. Our national 

 prototypes are preserved at the Bureau of Standards in 

 Washington. The two ends of one of them are shown below. 

 The only multiple of the meter in general use is the kilo- 

 meter, equal to 1000 meters. It is used to measure such 

 distances as are expressed in miles in the English system. 



ENDS OF METER BAR 



The Common Units in the Metric System are 



1 kilometer (km.) = 1000 meters (m.) 



1 meter =100 centimeters (cm.) 



1 centimeter =10 millimeters (mm.) 



The Common Units in the English System are : 



1 mile (mi.) = 5280 feet (ft.) 



1 yard (yd.) = 3 feet 



1 foot =12 inches (in.) 



By Act of Congress in 1866 the legal value of the yard 

 is tftf meter ; conversely the meter is equal to 39.37 inches. 

 The inch is, therefore, equal to 2.540 centimeters. 



