Light 193 



small gap between two pieces of carbon and generating intense 

 heat and light. Such a light is brilliant, but hard to keep adjusted. 

 The incandescent light depends upon a thin wire heated until it 

 glows by the passage of an electric current through it. This wire 

 is kept in a vacuum or in a special gas within a glass bulb, as 

 exposure to the air at high temperature would burn it up. 



SUMMARY 



The sun is the source of natural light. Light is one form of 

 radiant energy. 



Light waves travel from the sun at the rate of about 186,000 

 miles per second and radiate outward in all directions. 



All objects are seen by light waves that pass through the ether 

 from them to the eye. 



A light ray is a single line of light. 



A beam of light is a group of parallel rays. 



Materials may be transparent, translucent, or opaque. 



Color is due to the length of light waves, each color having 

 its own length of wave. 



A shadow is a dark space caused when an opaque body stops 

 the passage of light waves. 



Reflected light means light sent back from an object upon 

 which it falls. 



A beam of light when passing at an angle from one medium 

 into another of different density becomes bent, or refracted. 



The spectrum is a band of seven colors which appears when 

 sunlight is broken up by passing through a prism. 



The rainbow is a natural spectrum. 



A lens is a piece of transparent glass so made that its surfaces 

 are not parallel, and at least one is curved. There are two general 

 classes of lenses, convex, to focus light, and concave, to diffuse it. 



Nearsightedness is caused by inability of the eye to accom- 

 modate itself to distant vision, and farsightedness by inability to 

 accommodate itself to close vision. 



FACT AND THOUGHT QUESTIONS 



1. What are light waves? 



2. At what rate does light travel from the sun? 



