SUNBEAMS AND THEIR WORK. 
37 
But perhaps you will ask, if no one has ever seen 
these waves or the ether in which they are made, 
what right have we to say they are there ? Strange as 
it may seem, though we cannot see them we have 
measured them and know how large they are, and how 
many can go into an inch of space. For as these tiny 
waves are running on straight forward through the 
room, if we put something in their way, they will have 
to run round it ; and if you let in a very narrow ray of 
light through a shutter and put an upright wire in the 
sunbeam, you actually make the waves run round the 
wire just as water runs round a post- in a river; and 
FIG. 5. A, hole in the shutter ; B, wire placed in the beam of 
light ; S S, screen on which the dark and light bands are 
caught. 
they meet behind the wire just as the water meets in a 
V shape behind the post. Now when they meet, they 
run up against each other, and here it is we catch 
them. For if they meet comfortably, both rising up 
in a good wave, they run on together and make a 
bright line of light ; but if they meet higgledy-pig- 
