Page:Popular Science Monthly Volume 16.djvu/178

 

Fig. 20.

 

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 deflect 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;