7 8 ELEMENTARY SCIENCE 



and thus give us what we call water-power, the water 

 must be lifted to the high parts of the land from which it 

 flows down. The force which does this is, as has been 

 suggested, the heat of the sun. So it is to the sun, to its 

 heat in one case and to its light in the other, that we must 

 finally go back when we are seeking an explanation of 

 water-power and of steam-power. Thus we see that here, 

 as everywhere in nature, we have an endless chain of causes 

 and effects, and that the sun is the great original source of 

 the energy we see displayed on earth. 



QUESTIONS 



1. Explain why waterfalls are useful. 



2. Where did the energy that runs your watch come from? 



3. How would you compute the power that could be generated 



by Niagara Falls? 



4. How is power transmitted? 



3. Explain the turbine. Why is it better than the old-fashioned 

 water-wheel ? 



6. What is a horse-power? A foot-pound? 



7. What originally furnished the energy of the waterfall ? 



8. Explain the steam-engine. 



9. What is the difference between a water-turbine and a steam- 



turbine ? 



10. What put the energy into coal? 



11. Where did all energy come from originally? 



