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 511ed 

 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 ox 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 Las, 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 it is 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, nebulte, and stars have an identical constitution. The 

 nebulfe 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 nebula3 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 tbere are many cogent objections. In the 

 first place, althoui.'h 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 vahd objection, 

 the spectrum of the bright line nebulae is, according to Professor 

 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 tlie nebular hypothesis, which for a 

 time was called in question, has been restored to its old place, as 

 offeiing the best solution of the evolution of the universe, 



Mr. Eoberts' photograph of the great aebula in Andromeda has been 

 of great value in throwing light on the subject of nebular evolution 



