CONCAVE MIRRORS. 



439 



If a luminous point be not in the centre, but some- 

 what above it, although at the same distance from the 

 mirror as the centre, as A in fig. 249, then the incident 

 rays do not coincide with the perpendiculars at the 

 points of incidence: they are somewhat above these 

 perpendiculars, and consequently the reflected rays will 



R 



UNIVKUSITY 



.JALLL'V. 



be as much below, and converge to a point a y which is 

 the image of A. In the figure the full lines represent 

 the incident and reflected rays of light, the dotted lines 

 are the perpendiculars at the points of incidence. 



If the light emitted by A is of sufficient intensity, 

 the image formed by the convergence of the reflected 

 rays may be received at a upon a small screen, and 

 this image can be clearly seen in various directions ; if 

 the screen is translucent, it will be seen on both sides. 

 If no screen is placed at a for the reception of the image, 

 the latter can only be seen by looking in the direction 

 of the mirror itself; the eye will then receive the rays 

 which proceed beyond a, after having crossed at that 

 point, and the same impression will be produced as if 

 the rays actually proceeded from a. 



