, and so
far as we have learnt about it in this book everything in it seems
orderly: the planets go round the sun and the satellites go round the
planets, in orbits more or less regular; there seems no place for
anything else. But when we have considered the planets and the
satellites, we have not exhausted all the bodies which own allegiance to
the sun. There is another class, made up of strange and weird members,
which flash in and out of the system, coming and going in all directions
and at all times--sometimes appearing without warning, sometimes
returning with a certain regularity, sometimes retiring to infinite
depths of space, where no human eye will ever see them more. These
strange visitors are called comets, and are of all shapes and sizes and
never twice alike. Even as we watch them they grow and change, and then
diminish in splendour. Some are so vast that men see them as flaming
signs in the sky, and regard them with awe and wonder; some cannot be
seen at all without the help of the telescope. From the very earliest
ages those that were large enough to be seen without glasses have been
regarded with astonishment. Men used to think that they were signs from
heaven foretelling great events in the world. Timid people predicted
that the end of the world would come by collision with one of them.
Others, again, fancifully likened them to fishes in that sea of space in
which we swim--fishes gigantic and terrifying, endowed with sense and
will.

It is perhaps unnecessary to say that comets are no more alive than is
our own earth, and as for causing the end of the world by collision,
there is every reason to believe the earth has been more than once right
through a comet's tail, and yet no one except scientific men even
discovered it. These mysterious visitors from the outer regions of space
were called comets from a Greek word signifying hair, for they often
leave a long luminous trail behind, which resembles the filaments of a
woman's hair. It is not often that one appears large and bright enough
to be seen by the naked eye, and when it does it is not likely to be
soon forgotten. In the year 1910 such a comet is expected, a comet
which at its former appearance compelled universal attention by its
brilliancy and strangeness. At the time of the Norman Conquest of
England a comet believed to be the very same one was stretching its
glorious tail half across the sky, and the Normans seeing it, took it as
a good omen,