7 
you that this theory was developed by Kant and Laplace into the 
so-called nebular hypothesis. This hypothesis assumes that the 
entire space now occupied by the solar system was originally 4lled 
with a vapourous mass, out of which were evolved the planets, 
satellites, and the sun himself, the condensation of this nebulous 
matter giving rise to energy, sufficient to generate both light and 
heat. So great indeed is the heat induced by this process of 
shrinkage that, according to Helmholtz, the sun’s present 
temperature would be maintained by the contraction ot two hundred 
and twenty feet of his diameter per annum. Whether the sun is 
growing hotter or colder, or only maintaining his temperature is 
not certainly known. The nebular hypothesis bas, however, been 
questioned by many scientists, who favour the theory of evolution 
from meteorites, which was first propounded by Faye, and which 
suggests a totally different succession of events, in which the outer 
planets were formed last. The meteoric hypothesis, as itis called, 
has found a warm supporter in Mr. Norman Lockyer, who also, 
like the champions of the nebular hypothesis, bases his views on 
spectroscopic evidence, which, he maintains shows that comets, 
meteors, nebule, and stars have an identical constitution. The 
nebulz he considers to be meteor swarms which not yet been drawn 
into the solar system. As the individual meteorites are drawn 
together by the force of gravity, the nebula grows more compact, 
until from the heat evolved by the clashing of these tiny spheres 
their substance is so volatilised that the nebule is transformed into 
a glowing star, like Sirius, which is far hotter than the sun himself, 
As volatilisation ceases, the star cools, gradually grows less 
luminous, and eventually a dark star is formed. Thus the universe 
and its countless worlds are accounted for by this ingenious theory 
to which nevertheless there are many cogent objections. In the 
first place, althoush the number of meteors or falling stars is 
legion, we can hardly imagine it to have been great enough to 
form the myriad worlds around us. In the second place, meteors 
being complex bodies, we are no nearer the origin of matter, for no 
theory has been broached to account for the birth of the primordial 
meteorite. Thirdly, and I think this is the most valid objection, 
the spectrum of the bright line nebule is, according to Protessor 
Higgins, by no means the same as would be produced by collision 
of meteorites such as those which have been analysed in the 
_ laboratory. . The meteoric hypothesis therefore is fast losing favour 
with the scientific world, and the nebular hypothesis, which for a 
time was called in question, has been restored to its old place, as 
offering the best solution of the evolution of the universe, 
Mr. Roberts’ photograph of the great nebula in Andromeda has been 
of great value in throwing light on the subject of nebular evolution 
