152 MECHANICS 



entire French system is decimal as we shall see later in 

 our science. 



The next measurement after length is area. Area 

 is the surface of the thing measured and is found by 

 multiplying the length by the width, if the surface has all 

 right angles. How many degrees in a right angle? We 

 express area in square feet, square yards, or square miles. 

 We also have another standard called the acre. Can yon 

 tell how many square feet there are in an acre? Not an 

 easy number to remember, is it? Many of our standards 

 are not very convenient but we do not think much about 

 them since we have always had them. It is only when 

 we learn of a better method of doing something that we 

 realize how much we have missed up to that time. The 

 French acre, while it is about two and one-half times as 

 large as our acre, is 100 meters long and 100 meters wide. 

 This makes 10,000 square meters and is much more easily 

 remembered than the number of square feet in our acre. 

 For science work we use the small measure as in the case 



of length. It is the square centimeter. 

 - Next after area is volume. Volume is the 



space occupied by a solid body or it is the 

 space within a hollow body. The volume of a 

 [sol body having its sides at right angles to one 

 (1"| another can be obtained by multiplying to- 

 gether its length, width, and depth. The result 

 is expressed in cubical measure, such as cubic 

 inches, cubic feet, cubic yards, and, in the case 

 of wood, as cords. How many cubic feet in a 

 cord? The French system uses the cubic 

 meter. For ordinary science work we shall 

 use the cubic centimeter. A measure like the 



