optics. C ZS5 



Thus, for instance, light is more refracted in 

 passing from air into glass, than from air into 

 water; glass being denser than water. 



To prove the refraction of light, take an empty 

 basin into a dark room ; make a small hole in the 

 window shutter, so that a beam of light may fall 

 upon the bottom at a (Fig. 4.), where you may 

 make a mark. Then fill the basin with water, 

 without moving it out of its place, and you will 

 see that the ray, instead of falling upon a y will 

 fall at b. 



If a piece of looking-glass be laid in the bottom 

 of the basin, the light will be reflected from it, 

 and will be observed to suffer the same refraction 

 as in coming in ; only in a contrary direction. 



If the water be made a little muddy, by putting 

 into it a few drops of milk, and if the room be 

 rilled with dust, the rays will be rendered much 

 more visible. 



The same may be proved by another experiment. 

 Put a piece of money into the basin when empty, 

 and walk back till you have just lost sight of the 

 money, which will be hid by the edge of the basin. 

 Then pour water into the basin, and you will see 

 the money distinctly, though you look at it exactly 

 from the same spot as before. 



If the rays of light fall upon a piece of flat 

 glass, as L G (Fig. 1.), they are refracted into a 

 direction nearer to the perpendicular, as described 

 above, while they pass through the glass; but after 

 coming again into air, they are refracted as much 

 in the contrary direction; so that they move 

 exactly parallel to what they did before entering 

 the glass. But, on account of the thinness of the 

 glass, this deviation is generally overlooked, and it 

 is considered as passing directly through the glass. 



