nfinitely in every direction, and if it has no absorbing or weakening
effect on the vibrations which it transmits, we cannot escape from the
conclusion that practically all the rays of light ever emitted by all
the stars must chase one another eternally through the never-ending
abysses of space.

[38] _Planetary and Stellar Studies_, by John Ellard Gore, F.R.A.S.,
M.R.I.A., London, 1888.

CHAPTER XXVII

THE BEGINNING OF THINGS

LAPLACE'S NEBULAR HYPOTHESIS

Dwelling upon the fact that all the motions of revolution and rotation
in the solar system, as known in his day, took place in the same
direction and nearly in the same plane, the great French astronomer,
Laplace, about the year 1796, put forward a theory to account for the
origin and evolution of that system. He conceived that it had come into
being as a result of the gradual contraction, through cooling, of an
intensely heated gaseous lens-shaped mass, which had originally occupied
its place, and had extended outwards beyond the orbit of the furthest
planet. He did not, however, attempt to explain how such a mass might
have originated! He went on to suppose that this mass, _in some manner_,
perhaps by mutual gravitation among its parts, had acquired a motion of
rotation in the same direction as the planets now revolve. As this
nebulous mass parted with its heat by radiation, it contracted towards
the centre. Becoming smaller and smaller, it was obliged to rotate
faster and faster in order to preserve its equilibrium. Meanwhile, in
the course of contraction, rings of matter became separated from the
nucleus of the mass, and were left behind at various intervals. These
rings were swept up into subordinate masses similar to the original
nebula. These subordinate masses also contracted in the same manner,
leaving rings behind them which, in turn, were swept up to form
satellites. Saturn's ring was considered, by Laplace, as the only
portion of the system left which still showed traces of this
evolutionary process. It is even probable that it may have suggested the
whole of the idea to him.

Laplace was, however, not the first philosopher who had speculated along
these lines concerning the origin of the world.

Nearly fifty years before, in 1750 to be exact, Thomas Wright, of
Durham, had put forward a theory to account for the origin of the whole
sidereal universe. In his theory, however, the birth of our solar system
was treated merely as an incident