Explosive and Whirling Nebulæ

One of the most surprising triumphs of celestial photography was
Professor Keeler's discovery, in 1899, that the great majority of the
nebulæ have a distinctly spiral form. This form, previously known in
Lord Rosse's great ``Whirlpool Nebula,'' had been supposed to be
exceptional; now the photographs, far excelling telescopic views in
the revelation of nebular forms, showed the spiral to be the typical
shape. Indeed, it is a question whether all nebulæ are not to some
extent spiral. The extreme importance of this discovery is shown in
the effect that it has had upon hitherto prevailing views of solar and
planetary evolution. For more than three-quarters of a century
Laplace's celebrated hypothesis of the manner of origin of the solar
system from a rotating and contracting nebula surrounding the sun had
guided speculation on that subject, and had been tentatively extended
to cover the evolution of systems in general. The apparent forms of
some of the nebulæ which the telescope had revealed were regarded, and
by some are still regarded, as giving visual evidence in favor of this
theory. There is a ``ring nebula'' in Lyra with a central star, and a
``planetary nebula'' in Gemini bearing no little resemblance to the
planet Saturn with its rings, both of which appear to be practical
realizations of Laplace's idea, and the elliptical rings surrounding
the central condensation of the Andromeda Nebula may be cited for the
same kind of proof.

But since Keeler's discovery there has been a decided turning away of
speculation another way. The form of the spiral nebulæ seems to be
entirely inconsistent with the theory of an originally globular or
disk-shaped nebula condensing around a sun and throwing or leaving off
rings, to be subsequently shaped into planets. Some astronomers,