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Lire Is a C 



s a v^oncern 



or Matter and Energy 



We live in a universe of substance and force. Everything that we can discern 

 with our senses is either one or the other, matter or energy. So far as they are 

 known, matter and energy are always associated. They are in the grass beneath 

 our feet, the wind and the rain, our food and our use of food. Even a little 

 understanding of the character and relationships of matter and energy throws 

 light upon the lives of plants and animals; it may be the eyeshine of a cat in 

 the dark, the song of a wood thrush, the drip of sweat from the skin, the heat 

 of fever, the chnch of muscles. 



Matter 



Our bodies are composed of matter. It is all around us: books, plants, ani- 

 mals, sugar, smoke, gasoline, the earth, the planets, and the far-off galaxies, 

 each of them Uke the Milky Way of which our own solar system is a part. 

 What are these things? What is matter? A good deal has been learned about 

 its structure mostly during the last part of the nineteenth and the first part of 

 the twentieth centuries. In its analysis all the roads have led toward electricity. 

 But nobody knows what matter is because no one yet understands electricity. 



All matter is composed of invisible atoms; there are millions of billions of 

 them in a drop of water, each one containing extraordinarily minute electrical 

 particles. The electrical nature of living matter has been known in one way or 

 another for a long time, but in recent years more and more evidences of it have 

 been discovered. The Italian anatomist, Luigi Galvani (1737-1789) was 

 observing a freshly killed frog hung from an iron fence by a copper wire 

 hooked under the sciatic nerve when he noticed that the muscles twitched 

 whenever the wind-blown legs touched the iron fence. Thus a century and a 

 half ago Galvani discovered that living matter conducts electricity and re- 



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