60 THE CREATION OF MATTER 



line of incidence to any point in the line of reflection, a 

 beam of light chooses the shortest course, follows the 

 path in which it will make the journey in the shortest 

 time. The waves of a ray of light dart on a mirror, 

 strike it and rebound, imparting the larger portion of 

 their reflected motion to the ether lying in a line drawn 

 in the plane of incidence, and making with the perpendi- 

 cular an angle equal to the angle of incidence. On the 

 parts near the mirror everything depends, and never do 

 they fail, never do they act disorderly. They are always 

 true to their kind. They know in what direction to 

 forward the energy they receive, and initiate a new wave 

 in the right plane at the right angle. There is not a 

 point of the ether that would hesitate for the infini- 

 tesimal fraction of a second, that would not with the same 

 quickness make the same choice. Such perfection of 

 action is too wonderful for us, too clear in its meaning to 

 leave room for mistake. It makes evident the perfection 

 of the sameness of the ether throughout all its borders. 



Refraction. When light falls on a transparent sub- 

 stance, a portion enters and passes through. It takes, 

 however, a new direction, and is bent or refracted towards 

 the perpendicular. The size of the angle of incidence 

 bears to that of refraction a constant ratio. For the same 

 substance it is always the same. For different substances 

 it is different. Its velocity is also affected, but always in 

 the same measure in the same substance, and in different 

 measures in different substances. In the midst of aggre- 

 gated molecules the ether cannot vibrate with the same 

 ease as in a vacuum. It is hindered. The direction of 

 its rays is changed; the velocity is diminished. The 

 molecules take away from the energy and bend the action 

 into a new line. But all the molecules of the same 

 substance act on it in the same manner and measure. 



