43 



CHAPTER III 



MEASUREMENT OF WEIGHT 



24. Before considering the subject proper of this 

 chapter, we will deal with the meanings of some words in 

 common use, with especial reference to their application 

 in scientific work. First on our list we will put the 

 word "matter". Much learning has been expended 

 on the exact definition of matter, but for our purposes 

 it will be sufficient to consider that " Matter includes 

 everything that we can handle". Thus iron, water, 

 air are all forms of matter, since we can handle them, 

 weigh them, and preserve them for further examina- 

 tion. On the other hand thoughts, heat, and sleep 

 are not composed of matter, since we cannot so treat 

 them. 



The word "substance" means "kind of matter". 

 Thus iron, water, and air are substances and when we 

 say that iron is a hard substance we mean that all 

 pieces of iron are hard, not simply that one special 

 sample exhibits this quality. When we wish to speak 

 of a special piece of any substance we call it a " body ". 

 Thus we say that a 56 Ib. iron weight is a hard body, 

 made of the substance iron. 



Each body that exists contains a certain quantity 

 of matter. For example, the 56 Ib. weight mentioned 

 above contains a certain quantity of iron, and, as long 

 as the weight is protected from the action of sub- 

 stances or forces which may damage the iron in any 

 way, the quantity of iron present in the weight does not 

 alter, as far as we are able to judge in the present 



