142 



Common Science 



209. Unevenness in a window pane makes telephone wires seen 



through it look crooked and bent. 



210. You can see the image of a star even in a shallow ouddle. 



Source 



Focus 



FIG. 69. When the light from one point goes through the lens, it is bent and 

 comes together at another point called the focus. 



SECTION 24. Focus. 



How can you take pictures with a camera? 

 What causes the picture in the camera to be inverted ? 

 Why is a magnifying glass able to set things on fire when 

 you let the sun shine through it? 



In your eye, right back of the pupil, there is a flat- 

 tened ball, as clear as glass, called the lens. If the 

 lens were left out of your eye, you never could see any- 

 thing except blurs of light and shadow. If you looked 

 at the sun 'it would dazzle you practically as much as 

 it does now. However, you would not see a round sun ? 

 but only a blaze of light. You could tell night from day 

 as well as any one, and you could tell when you stepped 

 into the shade. If some one stepped between you and the 

 light, you would know that some one was between you 

 and the light or that a cloud had passed over the sun, - 

 you could not be quite sure which. In short, you could 

 tell all degrees of light and dark apart nearly as well as 

 you can now, but you could not see the form of anything. 



