380 REFLECTION OF LIGHT. 



of reflecting light. Then send another solar beam from the helio- 

 stat through the two windows of the box. Standing as before, 

 the beam may be traced to the box and beyond it, but within the 

 box all is darkness. 



594. Apparent Direction of Bodies. Every 



point of a visible object sends a cone of rays to the eye. 

 The pupil of the eye is the base of the cone. TJie point 

 always appears at the place where these rays seem 

 to intersect (i. e., at the real or apparent apex of the cone). 

 If the rays pass in straight lines from the point to the eye, 

 the apparent position of the point is its real position. If 

 these rays be bent by reflection, or in any other manner, 

 the point will appear to be in the direction of 

 the rays as they enter the eye. No matter how 

 devious the path of the rays in coming from the point to 

 the eye, this important rule holds good. 



595. Plane Mirrors; Virtual Images. If an 



object be placed before a mirror, an image of it appears 



behind the mirror. In- 

 asmuch as the rays of 

 the cone mentioned in 

 594 do not actually con- 

 verge back of the mirror, 

 there can be no real image 

 there. As there really is 

 no image behind the mir- 

 ror, we call it a virtual 



image. All virtual images 

 FIG. 281. , . , .,, . .. 



are optical illusions, and 



are to be clearly distinguished from the real images to be 

 studied soon. Each point of this linage will seem 

 to be as far behind the mirror as the correspond- 



