WEIGHTS AND MEASURES 11 



that by the weight of a unit volume of the substance. The 

 weight of a unit volume of any substance is called its density. 



FIG. 7. Weighing Scales. 

 These scales will weigh any body not more than 

 1 Ib. in weight. Its scale is graduated in ten- 

 thousandths of a pound . Such scales are used for 

 weighing small articles, screws, samples of paper, 

 etc. The weights are in front of the scales. The 

 object to be weighed is placed in the pan. 



The density of various substances has been compiled and refer- 

 ence tables have been prepared. The rule for determining the den- 

 sity of any substance may be written : 



Mass or weight in pounds 



Density = - 



Volume in cubic feet 



It follows therefore that : 



Weight = Density X Volume 



Weight 

 Volume = 



Density 



14. Speed. The distance over which a body passes in a 

 unit of time is called speed. Since the unit of space is usually 



