INORGANIC EVOLUTION. 29 



all the materials of tlie ring, and so a planet was formed. In 

 one instance there was a number of small centres of condensation, 

 and the zone of asteroids between Mars and Jupiter was the 

 result. Tliis process was repeated in the case of the incipient 

 planets, and satellites were formed in the same way. The central 

 nebula kept on contracting, and finally formed the Sun. All 

 these bodies continued condensing and losing heat, till they 

 finally attained their present condition. Against this theory it 

 may be stated that no nebula has yet been proved to rotate on 

 an axis. The fact that in the case of double stars the more 

 massive body is often the darker, seems also a difiiculty in the 

 way of accepting this theory. 



Sir Norman Lockyer has lately pronuilgated another theory of 

 the origin of the Sun and Stars, in many respects very different, 

 which he calls the Meteoric Hypothesis. He considers that 

 a nebula is not essentially a mass of incandescent gas, but rather 

 an immense cloud of meteorites. These meteorites, composed of 

 metals and metalloids much as we know them, are at com- 

 paratively considerable distances from each other and move 

 amongst themselves with extremely great rapidity. There are 

 continual collisions amongst them, causing tlieir partial 

 conversion into vapour and attended by the production of heat 

 and light. In process of time, under the action of gravity, 

 a condensation takes place in the centre of the meteor swarm, 

 forming the nucleus of a star. Other smaller condensations may 

 occur in other parts of the nebula, forming the nuclei of planets. 

 These condensations, being continually bombarded by meteoric 

 matter, grow not only larger but hotter and hotter, till at 

 length the meteorites are mostly used up and tlie central bodies 

 become converted into spheres of intensely hot incandescent gas. 

 The central mass forms a sun, and the smaller bodies become 

 planets which circulate round their primary under the influence 

 of gravity. As the sphere contracts it becomes hotter and 

 hotter till it reaches the highest attainable temperature, and the 

 condition of things we find in the hottest stars obtains, where he 

 estimates the temperature at about 30,000° C. As this process 

 goes on the elements become simplified and dissociated, till only 

 hydrogen, helium, proto-hydrogen, and some other proto-elements 

 remain. The history of the star henceforward is that of 

 a cooling body. As it continues to get cooler and cooler, the 

 metallic elements begin to appear and we get a spectrum 

 something like that of Sirius ; as the cooling process a,dvances 

 it attains the condition of our Sun, then that of the deep red 



