92 REFLECTED AND TRANSMITTED LIGHT. 



from it enters the eye, and not at all upon any changes in 

 direction or in character that it may have undergone be- 

 fore it enters. This is one of the principles on which illu- 

 sions are created, namely, by causing the light to enter 

 the eye in the way it would enter if it came really from 

 such a source as would correspond with the intended illu- 

 sion. 



There is one other curious thing to be observed in order 

 to understand clearly the philosophy of the ghost illusion, 

 and that is, that while opaque substances, such as the met- 

 als, will only reflect light, without transmitting any that 

 is, will throw back what falls upon its surface, but will not 

 allow any to pass through its substance from the other 

 side, transparent substances, like glass and water, will re- 

 flect apart of the light which falls upon them, and allow a 

 part to pass through. Thus we can look out through a 

 window into the street, and see what is there, and we can 

 also often see the reflection of the fire, or any other bright 

 object in the room, on the inside. When you look out 

 through a window from a room, and, still more, when you 

 look into a shop window from the street, it often happens 

 that you can not -see clearly on account of the "glare." 

 This glare is only the reflection of light from the glass on 

 your side of it, which reflection prevents your seeing clear- 

 ly the transmitted light, or, rather, seeing clearly the objects 

 on the other side, which can only be seen by transmitted 

 light. 



Thus, when you look into any such glass that of a win- 

 dow, for instance, some reflected and some transmitted light 

 comes to your eye that is, some light from your face, and 

 the other objects on the same side of the glass with your- 

 self, which is reflected, and some from the objects on the 

 other side which is transmitted, or, in other words, which 

 passes through : of these two it is the strongest that con- 



