A WONDERFUL WORLD 



Radio-activity is the mainspring of the universe. 

 The only elements so far known that undergo spon- 

 taneous change are uranium and thorium. One 

 pound of uranium contains and slowly gives out the 

 same amount of energy that a hundred tons of coal 

 evolves in its combustion, but only one ten-billionth 

 part of this amount is given out every year. 



Man, of course, reaps where he has not sown. 

 How could it be otherwise? It takes energy to sow or 

 plant energy. We are exhausting the coal, the nat- 

 ural gas, the petroleum of the rocks, the fertility of 

 the soil. But we cannot exhaust the energy of the 

 winds or the tides, or of falling water, because this 

 energy is ever renewed by gravity and the sun. 

 There can be no exhaustion of our natural mechani' 

 cal and chemical resources, as some seem to fear. 



I recently visited a noted waterfall in the South 

 where electric power is being developed on a large 

 scale. A great column of water makes a vertical fall 

 of six hundred feet through a steel tube, and in the 

 fall develops two hundred and fifty thousand horse- 

 power. The water comes out of the tunnel at the 

 bottom, precisely the same water that went in at 

 the top; no change whatever has occurred in it, yet 

 a vast amount of power has been taken out of it, or, 

 rather, generated by its fall. Another drop of six 

 hundred feet would develop as much more ; in fact, 

 the process may be repeated indefinitely, the same 

 amount of power resulting each time, without effect- 



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