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REFLECTION OF LIGHT. 



Such is the simple explanation of the effects of common plane mirrors. 

 If we stand before a mirror, each point of our persons emits light of a peculiar 

 color, which, diverging, falls on the surface of the mirror, and is reflected by 

 that surface as if it came from a person exactly resembling ourselves in form 

 and color, facing us, and standing at the same distance behind the mirror that 

 we are before it 



The form of an object thus rendered optically visible by a mirror is techni- 

 cally called its image. 



It is evident, from what has been stated, that if I stand before a mirror and 

 see my person in it, the image of my right arm being immediately opposite to 

 that arm and behind the mirror, will be the left arm of the image ; and in like 

 manner, the image of my left arm will be the right arm of the image. It is the 

 same with the images of all objects formed by plane reflectors : right becomes 

 left, and left right ; in other words, the image is reversed laterally. 



In some cases, as will be seen hereafter, optical images are not merely re- 

 versed laterally, but inverted vertically, so as to be seen upside down. This 

 is, however, not the case with plane mirrors ; for the head and the feet of the 

 image being on the other side of the mirror merely at the same distance be- 

 hind it as the head and the feet of the object are before it, the head will be at 

 the top and the feet at the bottom of the image. Objects are therefore seen 

 erect in plane mirrors. 



In cases where the arrangement from right to left is essential, the images 

 produced by plane mirrors become defective for the ordinary purposes of exhi- 



the point F, into another which will have the effect of diverging from the 

 point D. 



Now let us suppose a visible object, such as S S', fig. 3, placed in front of a 

 plane mirror, such as A B. Each point of that object will be a separate source 

 of light of the peculiar tint which may characterize the object. The light which I 

 proceeds from each of these points falling on the surface A B, will be reflected 

 as if it came from a corresponding point behind the mirror ; and an eye placed ( 

 anywhere before the mirror, as at O, will receive that light exactly as it would 

 receive it if the body which is at S S' were really at D D'. Consequently, 

 the eye will see an object at D D' exactly similar to S S'. 



Fig. 3. 



