222 ELEMENTARY SCIENCE 



is by merely obtaining the spectrum of its light. It is by 

 this means that scientists have been able to discover 

 important facts about the chemical nature of heavenly 

 bodies. So far as their researches have gone, they have 

 been unable to discover any element in the heavenly bodies 

 which is different from the elements here on earth. Does not 

 this suggest a common origin for all the heavenly bodies? 



Reflection of Light. We have noted that light may be 

 absorbed or may be reflected. Light-rays, unless inter- 

 fered with, travel in straight lines, 

 and the principle of their reflection 

 is the same as the principle which 

 governs the rebound of a ball. 

 That is, the angle of incidence is 

 equal to tlie angle of reflection (see 

 Fig. 80). We' see this principle in 

 operation when a billiard-ball re- 

 bounds from a cushion, or a tennis- 

 ball from a concrete sidewalk, or we may study it very in- 

 terestingly by observing the way in which mirrors reflect 

 images. 



Refraction. There are other things than absorption 

 and reflection which may happen to light-rays when they 

 encounter surfaces. One of these is refraction, which means 

 that the light-ray is bent. This explains why a spoon, 

 or an oar, or anything else, looks bent when partly immersed 

 hi water. It seems to bend at the point where it enters 

 the water. This is because of the greater density of water 

 as compared with air; because of this difference in density, 

 light passes through water in a direction somewhat altered 



