44 THE FAIRY-LAND OF SCIENCE. 
you see your own face by means of the very waves you 
threw off from it an instant before. 
But the reflected light-waves do more for us than 
this. They not only make us see things, but they 
make us see them in different colours. What, you 
will ask, is this too the work of the sunbeams ? Cer- 
tainly ; for if the colour we see depends on the size of 
the waves which come back to us, then we must see 
things coloured differently according to the waves they 
send back. For instance, imagine a sunbeam playing 
on a leaf: part of its waves bound straight back from 
it to our eye and make us see the surface of the leaf, 
but the rest go right into the leaf itself, and there 
some of them are used up and kept prisoners. The 
red, orange, yellow, blue, and violet waves are all 
useful to the leaf, and it does not let them go again. 
But it cannot absorb the green waves, and so it throws 
them back, and they travel to your eye and make you 
see a green colour. So when you say a leaf is green, 
you mean that the leaf does not want the green waves 
of the sunbeam, but sends them back to you. In the 
same way the scarlet geranium rejects the red waves ; 
this table sends back brown waves ; a white tablecloth 
sends back nearly the whole of the waves, and a black 
coat scarcely any. This is why, when there is very 
little light in the room, you can see a white tablecloth 
while you would not be able to distinguish a black 
object, because the few faint rays that are there, are 
all sent back to you from a white surface. 
Is it not curious to think that there is really no 
such thing as colour in the leaf, the table, the coat, 
or the geranium flower, but we see them of different 
