e that of a glowing cloud at sunset. Therefore
there can be no doubt that the colours are genuine enough, and are
telling us some message. This message we are able to read, for we have
begun to understand the language the stars speak to us by their light
since the invention of the spectroscope. The spectroscope tells us that
these colours indicate different stages in the development of the stars,
or differences of constitution--that is to say, in the elements of which
they are made. Our own sun is a yellow star, and other yellow stars are
akin to him; while red and blue and green stars contain different
elements, or elements in different proportions.

Stars do not always remain the same colours for an indefinite time; one
star may change slowly from yellow to white, and another from red to
yellow; and there are instances of notable changes, such as that of the
brilliant white Sirius, who was stated in old times by many different
observers to be a red star. All this makes us think, and year by year
thought leads us on to knowledge, and knowledge about these distant suns
increases. But though we know a good deal now, there are still many
questions we should like to ask which we cannot expect to have answered
for a long time yet, if ever.

The star colours have some meanings which we cannot even guess; we can
only notice the facts regarding them. For instance, blue stars are never
known to be solitary--they always have a companion, but why this should
be so passes our comprehension. What is it in the constitution of a blue
star which holds or attracts another? Whatever it may be, it is
established by repeated instances that blue stars do not stand alone. In
the constellation of Cygnus there are two stars, a blue and a yellow
one, which are near enough to each other to be seen in the same
telescope at the same time, and yet in reality are separated by an
almost incredible number of billions of miles. But as we know that a
blue star is never seen alone, and that it has often as its companion a
yellowish or reddish star, it is probable that these two, situated at an
enormous distance from one another, are yet in some mysterious way
dependent on each other, and are not merely seen together because they
happen to fall in the same field of view.

Many double stars show most beautifully contrasted colours: among them
are pairs of yellow and rose-red, golden and azure, orange and purple,
orange and lilac, copper-colour and blue,