by the law of attraction its particles would
have a tendency to coalesce and form aggregations of nebulous matter,
and that each of these, by the continued action of the same force, would
gradually condense and ultimately acquire the consistence of a star. In
the case of large irregular nebulae, numerous centres of attraction would
originate in the mass, round which the nebulous particles of matter
would arrange themselves; each nucleus, when condensation had been
completed, would become a star, and the entire nebula would in this
manner be transformed into a cluster of stars. Herschel believed that he
could trace the different stages of nebular condensation which result in
the evolution of a star. In large, faintly luminous nebulae the process
of condensation had only commenced; in others that were smaller and
brighter it was in a more advanced stage; in those that contained nuclei
there was evidence of nascent stars; and, finally, there could be seen
in some nebulae minute stellar points--new-born suns--interspersed among
the haze of the transforming mass. By this theory Herschel was able to
account for the phenomena associated with nebulous stars and the
supposed changes which were observed in some nebulae. The nebular
hypothesis as described by Herschel was not received with much favour,
nor did it unsettle much the belief that all nebulae were vast stellar
aggregations, and that their cloudy luminosity was a consequence of the
inadequacy of telescopic power to resolve them into their component
stars. Laplace, who was highly gifted as a geometrician, demonstrated
how the solar system could have been evolved in accordance with
dynamical principles from a slowly rotating and slowly contracting
spheroidal nebula. The rotatory motion of a nebula, in obedience to a
well-known mechanical law, increases as its density becomes greater, and
this goes on until the tangential force at the equator overcomes the
gravitational attraction at its centre. When this occurs, a revolving
ring of nebulous matter is thrown off from the parent mass, and by this
means equilibrium is restored between the two forces. As the rotatory
velocity of the nebula continues to increase with its contraction,
another ring is cast off, and in this manner a succession of revolving
rings may be detached from the condensing spheroid; each newly-formed
ring being nearer to the centre of the contracting mass and revolving in
a shorter period than its predecess