182 Our Surroundings 



these limits of frequency give the colors that appear in the rain- 

 bow between red and violet. The colors which are found in sun- 

 light are the rainbow colors, red, orange, yellow, green, blue, 

 indigo, and violet. All other colors are merely two or more of 

 these colors combined. 



The color of an object, then, is determined by the length of the 

 light waves which it sends to our eyes. Sometimes the color of 

 an object seems to change. This may depend on whether the 

 light waves come to us through the object or are reflected back 

 to us from its surface. A thin piece of gold leaf gives a very 

 good example of this change of color. If we place the gold leaf 

 between two pieces of glass to hold it in position, and then lay 

 it flat on the table, it will send back to us the yellow color of 

 gold; but if we hold it up between some source of light and our 

 eyes the color that comes to us is green. 



Experiment to Show that Light Rays Travel in Straight 

 Lines. Punch small holes in the centers of two pieces of card- 

 board, and set the pieces upright on separate supports, a few 

 inches apart. Light a candle and adjust the pieces of cardboard 

 so that you can look through both holes and see the flame 

 beyond. Is the line from the flame to your eye a straight line? 

 From this do you conclude that light rays travel in straight 

 lines ? 



Shadows. Any object that will not transmit light will cut 

 off or deflect it. Then a dark space, known as a shadow, will 

 be cast on the side away from the light. This shadow changes 

 with any change in the position of the light. For example, the 

 shadow of a tree cast by the sun at noon is far different from its 

 shadow in late afternoon when the sun is low in the west. 



Experiment to Show the Nature and Cause of Shadows. 

 Place a piece of white cardboard on a support between a lighted 

 candle and the wall in a darkened room. First, place the card- 

 board near the wall and note the type of shadow that is produced. 

 Then place the cardboard some distance from the wall and note 

 the shadow formed. The first observation will reveal a clear-cut 

 dark shadow. The second will give a rather indistinct shadow, 

 dark in the center and somewhat lighter at the edges. 



