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THE POPULAR SCIENCE MONTHLY. 



I first turn on the induction-coil slightly, so as not to bring out 

 its full power. The focus is now playing on the metal, raising it 

 to a white-heat. I bring a small magnet near, and you see I can de- 

 flect the focus of heat just as I did the luminous focus in the other 

 tube. By shifting the magnet I can drive the focus up and down or 

 draw it completely away from the metal and leave it non-luminous. 

 I withdraw the magnet, and let the molecules have full play again ; 



