470 TRANSFERRING AND TRANSFORMING ENERGY 



of this kind. The screw is another example of a gain in 

 power with a corresponding loss in distance. The screw, 

 generally combined with the lever, is used in many ordinary 

 machines. The jackscrew (Figure 146), copy-press, and vise 

 are examples of combinations of these two simple machines. 



Man's Most Important Energy Transformers. Perhaps 

 the first of nature's forces that man made use of was the 

 wind. He hoisted a sail for the wind to strike upon and to 



push him from place 

 to place. In about 

 the twelfth century 

 A.D. he discovered a 

 way of arranging 

 sails upon a wheel, 

 thus constructing a 

 windmill to help him 

 in his work. The 

 windmill is still used 

 in some places where 

 small power is needed, but the wind is no longer one of 

 man's main sources of energy. 



Running water early impressed man with its power. He 

 finally harnessed this power for grinding his grain and for 

 doing other kinds of work by means of the water wheel. 

 Many shapes of wheels were tried before the mighty tur- 

 bine, such as is used at Niagara Falls, was invented. It is 

 probable that more power is now developed at these Falls 

 than was developed by all the earlier water wheels ever 

 used. 



About the middle of the eighteenth century, a young 

 Scotchman, James Watt, invented a machine to utilize the 



AN ANCIENT SAILBOAT 



