164 Common Science 



that we can see is red. If the waves are a little shorter, 

 the light is orange ; if they are shorter yet, it is yellow ; 

 still shorter, green ; shorter still, blue ; while the shortest 

 waves that we can see are those of violet light. Black 

 is not a color at all ; it is the absence of light. We say 

 the night is black when we cannot see anything. A deep 

 hole looks black because practically no light is reflected 

 up from its depths. When you " see " anything black, 

 you really see the things around it and the parts of it 

 that are not perfectly black. A pair of shoes, for in- 

 stance, has particles of gray dust on them ; or if they 

 are very shiny they reflect part of the light that strikes 

 them as a white high-light. But the really black part 

 of your shoes would be invisible against an equally 

 black background. 



A black thing absorbs the light that strikes it and 

 turns it to heat. Here is an experiment that will prove 

 this to you : 



Experiment 52. (a) On a sunny day, take three bottles, 

 all of the same size and shape, and pour water out of a 

 pitcher or pan into each bottle. Do not run the water 

 directly from the faucet into the bottle, because sometimes 

 that which comes out of the faucet first is warmer or colder 

 than that which follows; in the pitcher or pan it will all 

 be mixed together, and so you can be sure that the water in 

 all three bottles is of the same temperature to begin with. 

 Wrap a piece of white cotton cloth twice around one bottle ; 

 a piece of red or green cotton cloth of the same weight twice 

 around the second bottle, and a piece of black cotton cloth 

 of the same weight twice around the third bottle, fastening 

 each with a rubber band. Set all three bottles side by side 

 in the sunlight, with 2 or 3 inches of space between them. 



