the gases round the sun are clashing violently together 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 to our earth and all other planets, must
not this quivering 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,, and you can
imagine how in the same way waves travel over the ether from the
sun to us.

Straight away from the sun on all sides, never stopping, never
resting, but chasing after each other with marvellous quickness,
these tiny waves travel out into space by night and by day. When
our spot of the earth where England lies is turned away from them
and they cannot touch us, then it is night for us, but directly
England is turned so as to face the sun, then they strike on the
land, and the water, and warm it; or upon our eyes, making the
nerves quiver so that we see light. Look up at the sun and
picture to yourself that instead of one great blow from a fist
causing you to see starts for a moment, millions of tiny blows
from these sun-waves are striking every instant on you eye; then
you will easily understand that his would cause you to see a
constant blaze of light.

But when the sun is away, if the night is clear we have light
from the starts. Do these then too make waves all across the