32 SCIENCE OF COMMON THINGS. 



Object of machinery. Perpetual motion. Sources of power. 



179 How do machines make additions to human power f 



They enable us to use the powers of natural agents, 

 as wind, water, steam; they also enable us to use ani- 

 mal power with greater effect, as when we move an 

 object easily with a lever, which we could not with the 

 unaided hand. 



ISO How do machines produce economy of human time f 

 They accomplish with rapidity what would require 

 the hand unaided much time to perform. A machine 

 turns a gun-stock in a few minutes ; to shape it by 

 hand would be the work of hours. 



181 How do machines convert objects apparently worthless into valuable, 

 products f 



By their great power, economy, and rapidity of ac- 

 tion, they make it profitable to use objects for manu- 

 facturing purposes which it would be unprofitable or 

 impossible to use if they were to be manufactured by 

 hand. Without machines, iron could not be forged 

 into shafts for gigantic engines ; fibres could not be 

 twisted into cables ; granite, in large masses, could not 

 be transported from me quarries. 



182 Why are so many attempts continually made to produce mechani- 

 cal engines which shatt generate perpetual motion f 



Because the projectors do not understand the great 

 truth, that no form or combination of machinery can, 

 under any circumstances, increase the quantity of power 

 applied. 



183 What is the object ef a machine f 



To receive and distribute motion derived from an 

 external agent, since no machine is capable of generat- 

 ing motion or moving-power within itself. 



184 What are the principal sources from whence power is obtained f 



Men and animals, water, wind, steam, and gunpow- 

 der. The power of all these may be ultimately re- 

 solved into those of muscular energy, gravity, heat, 

 and chemical affinity. 



185 Are there any other sources ofpotver ? 



Yes ; magnetism, electricity, capillary attraction, etc. ; 



