THE METRIC SYSTEM 



Volume = length X breadth X thickness. 



We can get the volume of an irregular solid by im- 

 mersing it in some liquid (Fig. 5). The body displaces 

 its own volume of liquid. 



The boundaries of a body, by which the mat- 

 ter of the body is separated from other matter, 

 or from space, are called surfaces. A cube has 

 six plane surfaces. A sphere has a uniformly 

 curved surface. A surface has two dimensions, 

 length and breadth. The boundaries of a sur- 

 face are lines, with only the dimension of length. 



pi 



\-w 



FIG. 5. 



7. Common Units of Length. The 

 unit of length used in Great Britain 



and the United States is the yard. Originally the yard 

 was probably the length of the King's arm, but this 

 changeable standard has become fixed, and is now the 

 length of a standard metal bar kept in London, with a 

 copy at Washington. The foot was originally the length 

 of the human foot, but became fixed as ^ of a yard. 

 The inch was fixed as A of a foot. 



8. The Metric System. The yard and its subdivisions 

 and multiples are still used for ordinary measurements 

 in this country and England, but on the continent of 

 Europe a different system prevails. This is called the 

 metric system ; its unit of length is the meter. It is a 

 decimal system, and has been adopted by scientific writers 

 the world over. The coinage of this country has long been 

 upon the decimal basis, and the names used for subdivi- 

 sions of the dollar are also used for subdivisions of the 



