94 INTRODUCTION TO GENERAL SCIENCE 



duction of heat by electricity ? Red-hot temperature is about 

 950 Fahrenheit. 



6. Attach one wire from the three cells to a file, and rub tn<> 

 other wire on it. What do you see ? 



c. If there is electric power in the building, the teacher may 

 show these effects to a startling degree. 



68. HEAT PRODUCES LIGHT 



We learned in Section 2 that heat is due to the motions of 

 the molecules, and in Section 3 that if the molecular motion 

 becomes rapid enough, the substance changes from a solid to a 

 liquid and then to a gas. These changes concern the material 

 alone. There is another effect which is produced by the 

 rapidly moving molecules, and we call the visible result light. 



All space between all bodies, and between the molecules of 

 every substance, is filled with what is usually called ether, and 

 sometimes light-bearing ether, to distinguish it from the an- 

 aesthetic. When the motions of the molecules are rapid 

 enough, waves similar to but very much smaller than water 

 waves are set up in this ether. All these waves of the ether 

 are electric waves, few of which affect the eye, but all of 

 which transmit energy. Since one form of energy can be 

 changed into all other forms, we obtain heat, light, and chemi- 

 cal effects from the sun. 



If a piece of metal is gradually heated, it begins to glow at 

 about 950 Fahrenheit, 525 Centigrade, and increases in 

 brightness up to dazzling white at about 2200 Fahrenheit, 

 1200 Centigrade. This is true only if the metal does not 

 turn into a gas. A very good example is the tungsten in- 

 candescent lamp, for metals, and the ordinary incandescent 

 lamp, for carbon. 



