38 THE FAIRY-LAND OF SCIENCE. 
gledy, one up and the other down, all in confusion, 
they stop each other, and then there is no light, but 
a line of darkness. And so behind your piece of 
wire you can catch the waves on a piece of paper, 
and you will find. they make dark and light lines one 
side by side with the other, and by means of these 
bands it is possible to find out how large the waves 
must be. This question is too difficult for us to work 
it out here, but you can see that large waves will make 
broader light and dark bands than small ones will, 
and that in this way the size of the waves may be 
measured. 
And now how large do you think they turn out 
to be? So very, very tiny that about fifty thousand 
waves are contained in a single inch of space ! I 
have drawn on the board the length of an inch,* and 
now I will measure the same space in the air between 
my finger and thumb. Within this space at this mo- 
ment there are fifty thousand tiny waves moving up 
and down ! I promised you we would find in science 
things as wonderful as in fairy tales. Are not these 
tiny invisible messengers coming incessantly from the 
sun as wonderful as any fairies? and still more so 
when, as we shall see presently, they are doing nearly 
all the work of our world. 
We must next try to realize how fast these waves 
travel. You will remember that an express train 
would take more than one hundred and seve.nty- 
five years to reach us from the sun ; and even a 
cannon-ball would take from ten to thirteen years 
to come that distance. Well, these tiny waves 
* The width of an inch may be seen in Fig. 13, p. 64. 
