90 REFLECTED AND TRANSMITTED LIGHT. 



fusedly together to the eye produce the sensation of white- 



There is another thing very curious about reflection, 

 which it is necessary to understand, in order that the man- 

 ner in which the ghost illusion is produced may be fully 

 intelligible. It is this, that the light reflected from any 

 mirror into the eye appears to come from an object lying 

 in the direction of the rays as they enter the eye. This 

 must of course be so, for the vision is produced in the eye, 

 and by the rays which enter into it, and its character is 

 of course determined entirely by the character of the rays 

 and the direction in which they are moving when they enter 

 it. In other words, the impression made upon the eye is 

 determined entirely by the condition of the rays of light 

 after they enter the organ. It can take no cognizance of 

 any changes these rays may have undergone on the way. 



This is illustrated in the engraving, where a portion of 

 the light from the candle is reflected from the mirror and 

 enters the eye. But you will see that it enters the eye 

 from such a direction, and with such a degree of conver- 

 gence as is sho-vn by the upper arrow as if it had come 

 from behind the glass. Of course it produces such an im- 

 age in the eye, and such a conception in the mind, as if it 

 had really come from that position ; just as if the glass, 

 instead of being a mirror, had been transparent, and the 

 light had come from an object behind it in the position 

 and in the light necessary to send rays directly to the eye, 

 such as were really sent to it by the reflection. 



In the engraving, only that portion of the rays from the 

 candle are represented which comes to the eye. Of course, 

 in fact, the radiance, in such a case, emanates from the 

 flame in every direction, and some portion of it is reflected 

 from every part of the surface of the glass, and is dispersed 

 to almost every part of the room. It follows from this 



