246 



SCIENCE OF COMMON THINGS. 



Lines of incidence and reflection. Why images appear inverted in water. 



The line of incidence. 



1645 When the light of our face is reflected back again from the mir- 

 ror, what is this returning path called f 



The line of reflection. 



1646 What is the angle of incidence f 



The angle between the line of incidence and the per- 

 pendicular. 



1647 What is the angle of reflection ? 



The angle between the line of reflection and the per- 

 pendicular. (See Fig. 52.) 



Let F B C (Fig. 53) be any surface ; D B a perpendicular to it. If a 

 marble were thrown from E to B, and bounded back to A, then E B D 

 would be the angle of incidence, and DBA the angle of reflection. 



1648 Why does the image of any object in water always appear in- 

 verted f 



Because the angles of incidence being always equal 

 to the angles of reflection, the light of the object, reflect- 

 ed to our eyes from the surface of the water, comes to 

 us with the same direction as it would have done, had 

 it proceeded directly from an inverted object in the 

 water. 



In Fig. 53, the light proceeding from the ar- 

 row-head, A, strikes the water at F, and is re- 

 flected to G and that from the barb, B, strikes 

 the water at E, and is reflected toG. A spec- 

 tator standing at G will see the reflected 

 lines, E G and F G, as if they proceeded di- 

 rectly from C and D. Now we always judge 

 of the position of an object according to the 

 direction in which the rays of light repre- 

 senting it come to the eye, and for this 

 reason the image of the arrow, A B, reflect- 

 ed from the surface of water, appears to be 

 located at C D. It is also plain that A (the more elevated object) will 

 strike the water, and be projected from it more perpendicularly than the 

 point B ; and therefore the image will seem inverted. 



164O If we lay a looking-glass upon the floor, with its face uppermost, 

 and place a candle beside it, why will the image of the candle seen in the 

 mirror by a person standing opposite to the candle, seem as much below the 

 surface of the glass as the candle itself stands above the glass ? 



Because the incident ray coming from the top of the 

 candle, strikes the surface of the glass, and is reflected 



Fig. 53. 



