122 THE REALITIES OF MODERN SCIENCE 



units have all been more or less arbitrarily chosen. 

 When the French, at the time of their Revolution, 

 by adopting the metric units/ laid the basis of the 

 present system of derived units, for the measurements 

 of all the magnitudes with which science deals, they at- 

 tempted to obtain a unit which would not be dependent 

 on an arbitrarily chosen standard, as was the English 

 ' ' yard, ' ' and would have a physical significance. There 

 was thus chosen the one ten-millionth part of the dis- 

 tance from the equator to the pole along the meridian 

 passing through Paris. Obviously, the determination 

 of this distance was a matter of astronomical observa- 

 tions rather than of direct measurement. The dis- 

 tance as finally determined was marked off by two 

 fine lines on a long platinum bar. This distance is 

 the "meter." 



As a matter of fact, later measurements showed 

 that it is not exactly the desired fraction of the earth's 

 quadrant. The distance is nevertheless the accepted 

 standard of length for all scientific as well as for many 

 commercial purposes. 



Even if the meter had been the desired fraction of 

 the earth's quadrant it would not have been a derived 

 unit but merely a submultiple of an arbitrarily chosen 

 length. The choice of a ten-millionth as the sub- 

 multiple made a unit of convenient size, a matter of 

 39.37 inches or about 10 per cent more than our familiar 

 unit of the yard. Of course, one idea in basing the 

 length of the unit on that of the earth's surface was to 

 obtain a unit which would be permanent and reproducible 

 without reference to a standard if the latter were de- 

 stroyed. A more logical choice of unit could be made 



