102 



CONSCIOUS NERVOUS OPERATIONS 



as fishes are immersed in the sea. Of this ether little- is 

 known, but it is supposed to transmit energy by waves. 

 The energy resident in vibrations of the ether is called 

 radiant energy, and it receives special names according to 

 its special, manifestations. For example, when it raises the 

 : temperature of objects^ which receive it, it is called radiant 

 <heat<; -wiier* it <oauses -chemical changes, it is called actinic 

 energy; in another form it is known as electricity; when it 

 affects the eye we call it light. All these forms of energy 

 extend in straight lines from the points of origin. Every 

 visible object sets up waves in the ether going in every 

 possible direction. Many millions of these waves are pro- 

 duced in a single second. 



134. Color. Some light waves give to the eye the sensa- 

 tion of red color; these are the longest of the light waves 

 perceived by the eye. Others give us the perception 

 of violet color; they are the shortest. Between them in 

 length are the waves of all the other colors. A union of 

 these many colors produces white light. 



135. The Spectrum. When a slender beam of sunlight 

 is allowed to pass through a small hole, and then through 



a glass prism into a 

 darkened room, the rays 

 of light falling upon a 

 screen are seen in an 

 oblong band of light of 

 many colors arranged as 

 we see them in the rain- 

 bow. This band of col- 

 Fig. 59. Separation of the rays of a . _. . 



beam of light by a prism. ors is called a spectrum 



(Fig. 59). 



136. Refraction. The separation of colors by the prism 

 is due to two facts. First, whenever a ray of light passes 



