234 FORMATION OF IMAGES. 



SEEING TIIEOUGn 



of these tubes is a piece of looking-glass like those below, 

 and they are placed in such a manner, at an angle, that 

 light from any object a candle, for instance, or a finger, 

 or a key placed in front of one of the tubes, is reflected 

 down into the channel in the stand, thence along the chan- 

 nel, and up through the other tube to the eye of the ob- 

 server. A big stone, then, or any other object perfectly 

 opaque, may be placed in the open space between the two 

 tubes, and a person looking through can see the candle or 

 the key appai-ently through the stone, by means of the 

 light which is carried down through the stand by the re- 

 flectors. The eye of the observer takes cognizance of the 

 rays as they enter the eye, and judges of the position of 

 the object from which they proceed solely from the direc- 

 tion in which they come in thus entering. 



And so it is in all cases. By means of reflectors of va- 

 rious mathematical forms, the course and relative direction 

 of any rays can be changed in almost any conceivable man- 

 ner, and made to enter the eye in any condition, as to di- 

 rection and power, that the experimenter may please; and 

 whatever may be the surface which reflects any light, if it 



