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 moment 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 171 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
take only seven minutes and a half to come the whole 91 millions
of miles. The waves which are hitting your eye at this moment
are caused by a movement which began at the sun only 7 1/2
minutes ago. And remember, this movement is going on
incessantly, and these waves are always following one after the
other so rapidly that they keep up a perpetual cannonade upon the
pupil of your eye. So fast do they come that about 608 billion
waves enter your eye in one single second.* I do not ask you to
remember these figures; I only ask you to try and picture to
yourselves these infinitely tiny and active invisible messengers
from the sun, and to acknowledge that light is a fairy thing.
(*Light travels at the rate of 190,000 miles, or 12,165,120,000
inches in a second. Taking the average number of wave-lengths in
an inch at 50,000, then 12,165,120,000 X 50,000 =