CHAPTER VI. 



MASS AND WEIGHT. 



12. MASS AND ITS MEASUREMENT. 



i. Measurement of mass. (a) Take two pieces of iron or brass, called in 

 ordinary language " pound " and " half pound weights " ; or a " pound " 

 and a " two pound " will do. Lift the two pieces of metal. One feels 

 heavier than the other ; that is, the masses are different. 



(6) Examine examples of British masses, e.g. an ounce, a pound, a half- 

 hundredweight. Also examine a box of metric masses, generally spoken 

 of as a box of " weights." 



(c) Compare a pound with a kilogram. Hang the 100-gram mass from 

 a spring balance, and notice that the downward pull or its weight is equal 

 to the weight of 3 ounces. What, then, is the British equivalent of the 

 weight of a kilogram ? It is evidently equal to the weight of 3 ounces x 10 

 =weight of 35 ounces = weight of 2 Ibs. (roughly). 



. The mass of any body is the quantity of matter it contains. 

 In our country the standard or unit of mass is the quantity of matter 



contained in a lump of plati- 

 num of a certain size which is 

 deposited with the Board of 

 Trade. This amount of matter 

 is called the Imperial Standard 

 Pound Avoirdupois, and the 

 mass of any other body is 

 spoken of as being a certain 

 number of times more or less 

 than the standard pound, that 

 is. as containing so many more 

 times as much (or as little) 

 matter than that contained in 

 the imperial standard pound. 

 Unfortunately, this is not a universal standard ; in France they have a 

 standard of their own. The French standard is kept at Sevres and is 

 called a kilogram, and the system of masses founded upon it is used 

 in all scientific work throughout the world (Fig. 20). 



lib 



1 Kilogram. 



FIG. 20. Comparative sizes of the British Stan- 

 dard Pound and the Metric Kilogram. 



