CHAPTER X 

 LIGHT AND ITS RELATION TO THE WORLD 



LIGHT WAVES 



Sources of Light. The great source of light is the sun. Fig. 105, 

 page 138. However, we have many minor sources, such as gas, oils, 

 and electricity. Bodies which give off light of their own accord are 

 said to be luminous, and bodies which give off reflected light are 

 said to be illuminated. The light which comes to us from the moon 

 and that from the paper on the wall are examples of reflected light. 

 Bodies which do not give off any light are said to be non-luminous. 



How Light Travels. Scientists believe that light travels in the 

 form of waves, not like the waves of the ocean, but waves which 

 travel in direct lines in all directions from the source of light. It 

 also takes time for this light to travel. It has been discovered that 

 light travels at the rate of 186,337 miles per second; in other 

 words, it takes about eight minutes for the light to come to us from 

 the sun. The length of time required for light to travel to us 

 from the North Star is about forty-six years. (How far away is the 

 North Star?) This means that if the North Star should be destroyed 

 to-night we would continue to receive light from it for a great many 

 years to come. There are some stars so far away from us that it 

 requires two hundred years for their light to reach us. 



The vibrations which cause light are called ether vibrations. 

 Ether is the invisible substance which fills all space. When the 

 vibrations are 



Trillions per second it produces the X-ray. 



2000 billions per second it produces the photographic ray. 



750 to 400 billions per second it produces light. 



230 billions per second it produces Hertzman waves for wireless. 



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