128 THE BKASOX WHY. 



'What is man, that thouart mindful of him? and the son of man that thou 

 visitesthim?" PSALSI vm. 



548. What is the relative intensity of primary and 

 reflected light ? 



The intensity of a reflection depends upon the power of the 

 reflecting surface. But, taking the sun and moon as the great 

 examples of primary and reflected light, the intensity of the sun's 

 light is 801,072 times greater than that of the moon. 



549. What is polarized light ? 



Polarized light is light which has been subjected to compound 

 refraction, and which, after polarization, exhibits a new series of 

 phenomena, differing materially from those that pertain to the 

 primary conditions of light. 



550. What are the chief deductions from the phenomena 

 observed under the polarization of light ? 



The polarization of light appears to conflrm in a high degree the 

 vibratory theory of light ; and to show that the vibrations of light 

 have two planes or directions of motion. The mast of a ship, for 

 instance, has two motions : it progresses vertically as the ship is 

 impelled forward, and it rolls laterally through the motion of the 

 billows. 



Something like this occurs in the vibrations of light, only the 

 vertical vibration is the condition of one ray, and the lateral 

 vibration is the condition of another ray, and the vibrations of these 

 two rays intersect each other in the solar ray. When these 

 vibrations occur together,, the ray has certain properties and 

 powers. But by polarization the rays may be separated, and the 

 result is two distinct rays, having different vibrations. 



It then appears that various bodies are transparent to these 

 polarized rays only in certain directions. And this fact is 

 supposed to show that bodies are made up of their atoms arranged 

 in certain planes, through or between which the lateral or the 

 vertical waves of light, together or singly, can or cannot pass ; and 

 that the transparency or the opacity of a body is determined by the 

 relation of its atomic planes to the planes of the vibrations of 

 light. 



Ordinary light, passing through transparent media, produces no 

 very remarkable effect in its course ; but polarized light appear* t* 



