to, but we can see
miniature rainbows which contain just the same colours as the real ones
in a number of things any time the sun shines. For instance, in the
cut-glass edge of an inkstand or a decanter, or in one of those
old-fashioned hanging pieces of cut-glass that dangle from the
chandelier or candle-brackets. Of course you have often seen these
colours reflected on the wall, and tried to get them to shine upon your
face. Or you have caught sight of a brilliant patch of colour on the
wall and looked around to see what caused it, finally tracing it to some
thick edge of shining glass standing in the sunlight. Now, the cut-glass
edge shows these colours to you because it breaks up the light that
falls upon it into the colours it is made of, and lets each one come out
separately, so that they form a band of bright colours instead of just
one ray of white light.

This is perhaps a little difficult to understand, but I will try to
explain. When a ray of white light falls on such a piece of glass, which
is known as a prism, it goes in as white light at one side, but the
three-cornered shape of the glass breaks it up into the colours it is
made of, and each colour comes out separately at the other side--namely,
from blue to red--like a little rainbow, and instead of one ray of white
light, we have a broad band of all the colours that light is made of.

Who would ever have thought a pretty plaything like this could have told
us what we so much wanted to know--namely, what the sun and the stars
are made of? It seems too marvellous to be true, yet true it is that for
ages and ages light has been carrying its silent messages to our eyes,
and only recently men have learnt to interpret them. It is as if some
telegraph operator had been going steadily on, click, click, click, for
years and years, and no one had noticed him until someone learnt the
code of dot and dash in which he worked, and then all at once what he
was saying became clear. The chief instrument in translating the message
that the light brings is simply a prism, a three-cornered wedge of
glass, just the same as those hanging lustres belonging to the
chandeliers. When a piece of glass like this is fixed in a telescope in
such a way that the sun's rays fall on it, then there is thrown on to a
piece of paper or any other suitable background a broad coloured band of
lovely light like a little rainbow, and this is called the sun's
spectrum, and the instrument by whi