334 



SCIENTIFIC AMUSEMENTS. 



mirror is in front, the radius of curvature being the same, so that 

 CF = GF = JCG. 

 Expt. 363. Formation of Images in Curved Mirrors. If an 



observer stand in front of a convex mirror, no matter what the 

 distance between himself and the face of the mirror may be, he 

 will always observe a reflected image (virtual image) of himself or 

 of any other object situated in front of the mirror ; and this image 

 will always be erect (not upside down) and diminished in size (smaller 

 than the actual object). Thus the arrow, AB, (fig. 179), in front 

 of the convex mirror, when seen by reflection appears to be situated 



Fig. 179. Virtual Image formed by Convex Mirror. 



at ab, behind the mirror, and nearer to it than its geometrical focus, 

 F, and smaller in size, because it obviously subtends a lesser angle 

 at the eye of the observer at 0. But if a concave mirror be used 

 instead of a convex one, the effect differs according to the situation 



of the object with respect to 

 the mirror ; if the object, AB, 

 (fig. 180) (say a candle flame) 

 be nearer to the mirror than 

 the geometrical focus, F, an 

 observer at in front sees 

 an erect virtual image at 

 ab, not diminished, as in the 

 case of a convex mirror, but 

 magnified, because it now 

 subtends a greater angle at 

 the observer's eye than the 

 actual object. 



If the flame be held as nearly as possible at the focus F, no 

 distinct image of any kind is seen, but only a blaze and blurr of 

 light ; whilst, if the object AB be held between the focus F and 

 the centre of curvature, C, a real inverted and magnified image, 

 ab, is formed further from the mirror than the centre of curvature 



Fig. 180. Virtual Image formed by 

 Concave Mirror. 



