304 



WELLS'S NATURAL PHILOSOPHY. 



When will the 

 image in a 

 looking-glaRS 

 appear distort- 

 ed? 



Bow is an ap- 

 parent change 

 of place caused 

 bj reflection f 



reflected perpendicularly ; if they fall upon it obliquely, 

 they will be reflected obliquely ; the angle of reflection 

 being always equal to the angle of incidence. 



If the two surfaces of mirrors are not parallel, or uneven, 

 then the rays of light falling upon it will not be reflected regu- 

 larly, and the image will appear distorted. 



661. We always seem to see an object in the 

 direction from which its rays enter the eye. A 

 mirror, therefore, which, by reflection; changes 

 the direction of the rays proceeding from an 

 object, will change the apparent place of the object. 



Thus, if the rays of a candle fall obliquely upon a, mirror, and are reflected 

 to the eye, we shall seem to see the candle in the mirror in the direction 

 in which they proceed after reflection. 



If we lay a looking-glass upon the floor, with its face uppermost, and place 

 a candle beside it, the image of the candle will be seen in the mirror, bj' a 

 person standing opposite, as inverted, and as much below the surface of the 

 glass as the candle itself stands above the glass. The reason of this is, that 

 the incident rays from the candle which fall upon the mirror are reflected to 



the eye in the same 

 ^^^- 236. direction that they 



would have taken, had 

 they really come from 

 a candle situated as 

 much below the sur- 

 face of the glass, as 

 the first candle was 

 above the surface. 

 This fact will be 

 clearly shown by re- 

 ferring to Fig. 236. 

 "When we look into a plane mirror (the common looking-glass) the rays of 

 light whicli proceed from each point of our body before the mirror will, after 

 reflection, proceed as if they came from a point holding a corresponding posi- 

 tion behind the mirror ; and therefore produce the same eflect upon the eye 

 of the observer as if they had actually come from that point. The imago 

 in the glass, consequently, appears to be at the same distance behind the 

 surface of the glass, as the object is before it. 



Let A, Fig. 237, be anv point of a visible object placed before a looking- 

 glass, M N. Let A B and A be two rays diverging from it, and reflected 

 from B and C to an eye at 0. After reflection they will proceed as if they 

 had issued from a point, a, as far beliind the surflice of the looking-glass 

 as A is before it — that is to say, the distance A N will be equal to the 

 distance N a. 



