130 Common Science 



thing around it light; everything stays absolutely 

 invisible. It is as if all things in the world except the 

 lights had put on some sort of magic invisible caps. 



We can strike a match and see its flame. We can see 

 a fire on the hearth. We may feel around for the in- 

 visible poker, and when we find it, we may put it in the 

 fire. When it becomes hot enough, it will glow red and 

 become visible. We can make a match head glow by 

 rubbing it on a wet finger. We can even see a firefly, 

 if one comes around. But only those things which are 

 glowing of themselves, like flames, and red-hot pokers, 

 and fireflies, will be visible. 



The reason why practically everything would be invis- 

 ible if there were no reflection of light is this : When 

 you look at anything, as a man, for instance, what you 

 really see is the light that hits him and bounces back 

 (reflects) into your eyes. Suppose you go into a dark 

 room and turn on an electric light. Instantly ripples 

 of light flash out from the lamp in every direction. As 

 soon as they strike the object you are looking at, they 

 reflect (bounce back) from it to your eyes. When light 

 strikes your eyes, you see. 



Of course, when you look at an electric lamp, or a 

 star, or the sun, or anything that is incandescent (so 

 hot that it shines by its own light), you can see it, whether 

 reflection exists or not. But most things you look at 

 do not shine by their own light. This book that you 

 are reading simply reflects the light in the room to your 

 eyes ; it would not give any light in a dark room. The 

 paper reflects a good deal of light that strikes it, so it 

 looks very light; the print reflects practically none of 



