REFLECTION OF LIGHT. 



bition. Thus a printed word, or an inscription, when held before a mirror, will 

 be altogether deranged ; it will have the same appearance to the eye as the ! 

 types have from which it is printed. 



REFLECTION AT CURVED SURFACES. 



I 



Whatever be the form of a curved surface, it may be conceived to consist of 

 separate parts of such small dimensions that each of them may be considered 

 as a portion of a sphere or globe ; and therefore if the principles which regu- 

 late the reflection of light from a spherical surface be known, the effects of 

 curved surfaces of other forms maybe easily investigated. We shall therefore 

 confine our observations here to the reflection of light from perfectly smooth 

 spherical surfaces. 



CONCAVE REFLECTORS. 



LetM A M', fig. 4, represent a portion of a concave spherical reflecting surface, 

 and let S represent a point from which light diverges ; let C be the centre of 

 the spherical surface. A ray of light falling from S upon the point I, will be 

 reflected in the direction I R, so as to make the angle RIG equal to the angle 

 SIC. If the point S be very near to or in the line* A C, and at a very great 

 distance from the reflector, then the point R will be at the middle of the dis- 

 tance C A, so that it will divide the radius C A into two equal parts. 



Fig. 4. 



If the point S be in any object, the corresponding point R will be its image, 

 and in like manner the images of all the other points will be formed. 



When a concave speculum is presented to a very distant object, an image of 

 that object will be formed in front of the speculum, and at a distance from it 

 equal to half its radius. This image, however, will be inverted. 



If the object be not at a very great distance from the reflector, its image 

 will be formed at a point farther from the surface than half the radius, and will 

 still be inverted. 



In a convex reflecting surface, the image of an object placed in front will be 

 formed behind the reflecting surface ; as in the case of a plane mirror, it will 

 be erect and smaller than the object. 



The positions assumed by the images of objects formed by concave and 

 convex reflectors, have rendered this species of mirrors amusing means of oc- 

 casional optical exhibition. 



If an object be placed in front of a convex mirror, its image will be formed 

 behind the mirror at a distance something less than half the radius of the con- 

 vexity. This image will be always erect, but will be smaller than the object ; 

 and the more distant the object is from the mirror, the smaller will be the 

 image. 



Whatever be the form of the object, the image will have a tendency to a 

 convex form, and consequently such mirrors always produce distortion. 



