ity, stars that have passed the meridian of life, and stars in a
condition of decay and on the verge of extinction. The observations of
astronomers have led them to conclude that this condition of 'youth and
age' exists among the stellar multitude; but the characteristics by
which it is distinguished are neither very obvious nor reliable.

The nebular theory is incapable of proof or demonstration; but modern
discoveries tend to support the accuracy of its conclusions, and its
principles have now been adopted by the majority of philosophic
thinkers. The physical changes which are going on in the nebulae towards
stellar evolution, or in fully formed stars towards dissolution, are so
slow that the life of an individual, or even the historical records of
the past, are incapable of furnishing any evidence of alteration in
their condition. A period of time infinitely greater than what has
elapsed since the birth of science must pass before anything can be
known of the life history of the stars; indeed, the allotted span of
man's existence on this planet may have terminated ere the evolution of
a large nebula into a star cluster can have taken place.

The nebular hypothesis was first propounded by Kant, who suggested that
the sun and planets originated from a vast and diffused mass of cosmical
matter. This theory was afterwards supported by Herschel and by the
great French astronomer Laplace. As a result of close and continued
observation of the different classes of nebulae, Herschel arrived at the
conclusion that there exists in space a widely diffused 'shining fluid,'
of a nature totally unknown to us, and that the nebulosity which he
perceived to surround some stars was not of a starry nature. He further
adds that this self-luminous matter 'seemed more fit to produce a star
by its condensation than to depend on the star for its existence.' His
sagacious conclusion with regard to the non-stellar nature of this
nebulous matter was afterwards confirmed by the spectroscope; for at
that time it was believed that even the faintest nebulae were
irresolvable star clusters.

In 1811 Herschel read a paper before the Royal Society in which he
propounded his famous nebular hypothesis, and stated his reasons for
believing that nebulae, by their gradual condensation, were transformed
into stars. Having assumed that there exists a highly attenuated
self-luminous substance diffused over vast regions of space, he
endeavoured to show that