REFLECTION AND REFRACTION. 227 



CHAPTER XXV. 



FORMATION OF IMAGES. 



LIGHT tends always to move in right lines in proceeding 

 from its source. There are, however, two very striking and 

 marked modes by which it is deflected or turned from its 

 course. The first is called reflection, and the second re- 

 fraction. 



When the light, in its progress, falls upon a liquid or a 

 solid surface that is opaque, a portion of it sometimes a 

 very large portion of it rebounds, as it were. This is 

 called reflection. When it falls upon any transparent liq- 

 uid or solid, it passes in ; but, except when it enters per- 

 pendicularly, it is bent somewhat out of its direct course 

 in entering, and also again in emerging on the farther side, 

 if it does emerge. Thus we may say, in general terms, that 



Reflection is the turning back of a ray of light, or a por- 

 tion of a ray, in falling upon a surface which does not al- 

 low it, or the whole of it, to pass through ; while 



Refraction is the bending of a ray of light, or a portion 

 of it, in entering and leaving a substance which does allow 

 it, or a part of it, to pass through. 



Probably many of the readers of this book may have 

 known this before, and they may also know some other 

 things that I am about to state, especially those in respect 

 to reflection. Indeed, some of these facts have already 

 been referred to in a preceding chapter. But, even if you 

 know certain facts individually and separately, it is a great 

 advantage to have them brought together and stated in a 

 systematic manner, so as to show them in their relations 



