SCIENCE OF COMMON THINGS. 31 



Application of power. What are machines ? 



PART n. 



APPLICATION OF THE LAWS AND PROPER 

 TIES OF MATTER TO THE ARTS. 



CHAPTER I. 



HOW WE APPLY POWEB. 



175 What is a machine f 



By a machine we understand a combination of me- 

 chanical powers adapted to vary the direction, applica- 

 tion, and intensity of a moving force, so (is to produce 

 a given result. 



176 What is the difference between a machine and a tool ? 



The difference between a machine and a tool is not 

 capable of very precise distinction. A tool is usually 

 'more simple than a machine : it is generally used by 

 hand, while a machine is generally moved by some 

 vther than human power. 



177 Does a machine ever create power, or increase the quantity of 

 power or force applied to it? 



A machine will enable us to concentrate or divide 

 any kind or quantity of force which we may possess, 

 but it no more increases the quantity of force than a 

 mill-pond increases the quantity of water flowing in 

 the stream. 



178 From what sources do we derive advantages by the use of machines 

 and manufactures f 



From the addition they make to human power ; 

 from the economy they produce of human time ; from 

 the conversion of substances apparently common and 

 worthless into valuable products. 



