124 FIRST YEAR COURSE IN GENERAL SCIENCE 



The light may be bent from the direction in which it enters; 

 and it may be separated into the rainbow colors of which 

 white light is composed. An object seen through a prism 

 held horizontally seems to be above or below its real place, 

 and the image is fringed with a band of colors. 



Raindrops act like prisms in separating sunlight into rain- 

 bow colors, and the colored light reflected to the observer 

 from many drops at once, makes a rainbow. The rainbow 

 is always seen in the part of the sky opposite the sun. 



FIG. 59. A PRISM 



Glass prisms used in the study of light have generally three faces. 1. If 

 a beam of light falls perpendicularly upon one face, it will not be bent on 

 entering the prism; why will it be bent on leaving the other side? 2. In 

 Fig. 59 the beam enters obliquely, is bent, passes out obliquely, and is bent 

 again. How many changes of medium are there? 3. What happens to the 

 rays composing the beam, besides change of direction? (The names of the 

 colors are violet, indigo, blue, green, yellow, orange, red.) 



A lens is a transparent body having two curved surfaces 

 or one curved and one plane. If a surface is like the inside 

 of a hollow sphere it is a concave surface; if like the outside, 

 it is a convex surface. When the surfaces are so combined 

 that the lens is thinner at the middle than at the edges, it 

 is a concave lens ; if the lens is thicker at the middle than at 

 the edges, it is a convex lens. A convex lens can be used as a 

 magnifying glass. When it is held a short distance from the 

 object examined, the eye of the observer receives light from 



