42 THE FAIRY-LAND OF SCIENCE 
brain : and the colour we see depends upon the number 
of waves which play upon 'the retina in a second. 
Do you think we have now rightly answered the 
question What is a sunbeam ? We have seen that it 
is really a succession of tiny rapid waves, travelling 
from the sun to us across the invisible substance we 
call "ether," and keeping up a constant cannonade 
upon everything which comes in their way. We have 
also seen that, tiny as these waves are, they can still 
vary in size, so that one single sunbeam is made up 
of myriads of different-sized waves, which travel all 
together and make us see white light; unless for some 
reason they are scattered apart, so that we see them 
separately as red, green, blue, or yellow. How they 
are scattered, and many other secrets of the sun-waves, 
we cannot stop to consider now, but must pass on to 
ask- 
What work do the sunbeams do for us f 
They do two things they give us light and heat It 
is by means of them alone that we see anything. When 
th room was dark you could not distinguish the table, 
the chairs, or even the walls of the room. Why? 
Because they had no light-waves to send to your eye. 
But as the sunbeams began to pour in at the window, 
the waves played upon the things in the room, and 
when they hit them they bounded off them back to 
your eye, as a wave of the sea bounds back from a 
rock and strikes against a passing boat. Then, when 
they fell upon your eye, they entered it and excited 
the retina^ and the nerves, and the image of the chair 
or the table was carried to your brain. Look around 
at all the things in this room. Is it not strange to think 
