Rural School Leaflet 725 



Sunlight comes to us from the sun in little waves or ripples called rays. 

 The finest waves or ripples that we can see are blue, and the coarsest are 

 red. Some of the waves are so fine and some are so coarse that they do 

 not affect the sight nerves in our eyes. The coarse ones are called 

 dark rays, or heat rays. 



If you drop a stone into a pool of quiet water, you will see the little 

 waves or ripples run out in all directions, forming circles, the center of 

 each being the place where the stone fell; but if you look closer, you will 

 see that each little wave moves away from the center in a straight line. 

 Light waves move away from the sun in all directions in straight lines 

 in just the same way; but when they strike an object, as a tree or a building, 

 they are stopped, and thus on the opposite side of the tree or building we 

 see its shadow. Many harbors along the ocean are closed in by great 

 walls of stone or concrete except for a small gateway through which the ships 

 enter. These walls are called breakwaters, and they stop the waves of 

 water as they roll in from the ocean in much the same way that a building 

 stops the waves of light and casts a shadow. We might call the quiet 

 water behind a breakwater a water shadow. 



There are some things that do not stop these little light waves, and 

 that therefore do not have any shadow. Can you think of anything that 

 will not cast a shadow when the sunHght falls on it? What about glass? 

 Although glass is hard and rather strong, the little light waves pass right 

 through it. Anything that stops the light waves is called opaque, and 

 anything through which the light waves will pass is called transparent. 

 How many transparent things can you think of? How many that are 

 opaque ? 



If you drop a stone into a pool of quiet water the little waves will run 

 out in circles quite fast ; but how fast do you suppose the little light waves 

 run out from the sun? What is the swiftest moving thing you can think 

 of in the world? An express train, perhaps. How far will it go while 

 you count ten? If you count right along it may take you about 5I seconds. 

 Try to count ten in 5^ seconds. In that time an express train would travel 

 500 feet. Do you know of an object about 500 feet from your schoolroom? 

 In the 5^ seconds while you count ten and an express train is going 500 

 feet, the little light waves running out from the sun travel a milhon miles. 



How can I help you to think of a million miles? Suppose you were to 

 get on an express train going 60 miles an hour, and you traveled on and 

 on, night and day, month after month, never stopping for coal or water 

 all through this year and nearly eleven months of next year, you would have 

 traveled just a million miles. But the distance you would travel on an 

 express train going 60 miles an hour in one year and eleven months, these 

 little waves of light travel in 5^ seconds, just while you count ten. 



