204 GENERAL SCIENCE 



pounds. If the dam is 12 feet high, the work which the 

 water would do per second would be 77,500 pounds X 

 12 feet, or 930,000 foot pounds. It would develop 

 930,000 4- 550 or 1690.9 horse power if there were no 





DAM IN THE ALLEGHENY RIVER 



waste. Such a stream would be valuable for running a 

 flour mill or other machinery, but the turbine installed 

 should be one which would develop about 1,000 horse 

 power, as all of the water could not be made to pass 

 through the wheel. 



137. Windmills. The toy wind wheel made of 

 paper and fastened to a stick with a pin, 

 illustrates the principle of the windmill. 

 The air strikes the curved blades of the 

 wheel at an angle and the wheel is thus 

 turned by the force of the air. The wheel 

 TOY WIND o f a windmill is made of strong blades of 

 wood or steel, sometimes curved like the 

 blades of a toy wheel; sometimes the blades are flat but 

 set at an angle so that the force of the wind causes the 



