SUNBEAMS AND THEIR WORK. 35 
quite as invisible as the Emperor's new clothes in 
Andersen's fairy-tale, only with this difference, that 
our invisible something is very active ; and though we 
can neither see it nor touch it we know it by its 
effects. You must imagine a fine substance filling all 
space between us and the sun and the stars. A 
substance so very delicate and subtle, that not only is 
it invisible, but it can pass through solid bodies such 
as glass, ice, or even wood or brick walls. This 
substance we call "ether." I cannot give you here 
the reasons why we must assume that it is throughout 
all space ; you must take this on the word of such 
men as Sir John Herschel or Professor Clerk-Maxwell, 
until you can study the question for yourselves. 
Now if you can imagine this ether filling every 
corner of space, so that it is everywhere and passes 
through everything, ask yourselves, what must happen 
when a great commotion is going on in one of the 
large bodies which float in it ? When the atoms ol 
the gases round the sun are clashing violently togethei 
to make all its light and heat, do you not think they 
must shake this ether all around them ? And then 
since the ether stretches on all sides from the sun tc 
our earth and all other planets, must not this quiver- 
ing travel to us, just as the quivering of the boards 
would from me to you ? Take a basin of water to 
represent the ether, and take a piece of potassium like 
that which we used in our last lecture, and hold it 
with a pair of nippers in the middle of the water. 
You will see that as the potassium hisses and the 
flame burns round it, they will make waves which 
will travel all over the water to the edge of the basin 
D 2 
