CHAP. xi. ASTRONOMY AND COSMIC THEORIES. 103 



even when we took account of the nebular hypothesis, 

 and tried to imagine a mass of elemental gaseous matter 

 occupying a sphere of the diameter of the orbit of Nep- 

 tune, gradually cooling and shrinking, leaving rings of 

 diffused matter behind it, which afterward broke up and 

 aggregated into the planets and satellites already known 

 to us, the hypothetical solution of the problem was 

 hardly satisfying, since it seemed difficult to understand 

 how so vast a plenum could be converted into an equally 

 vast vacuum, except for the few and remotely scattered 

 planetary systems as its sole relics. 



But the study of the long-despised and misunderstood 

 meteorites and falling stars has entirely changed our 

 conceptions of that portion of the universe of which our 

 sun is the centre. We are now led to regard it as more 

 nearly approaching a plenum than a vacuum. We 

 know that it is everywhere full of what may be termed 

 planetary and meteoric life full of solid moving bodies 

 forming systems of various sizes and complexities from 

 the vast mass of Jupiter, with its five moons, down to 

 some of the minor planets a few miles in diameter, and 

 just large enough to become visible by reflected light; 

 and again, downward, of all lesser dimensions to the 

 mere dust-grains which only become visible when the 

 friction on entering our atmosphere with the great 

 velocities due to their planetary motion round the sun 

 ignites and sometimes, perhaps, dissipates them. 



We here obtain a new conception of the possible 

 origin of the universe as we now see it, a conception 

 which originated with Professor Tait, and has been 

 forcibly advocated by Lockyer and a few other astrono- 

 mers, which is that both the solar system and the stellar 



