THE BIRTH OP THE SUN AND PLANETS 13 



interpretation of world-development that has passed 

 beyond the stage of hesitation. Stars or suns are born 

 of nebulae, and, under certain conditions, will return to 

 nebulas. The solidification into globes and the clothing 

 of some of those globes with living mantles are episodes 

 in this stupendous rythm of movement from nebula to 

 nebula. Our task is to trace the condensation of nebulas 

 into solid bodies, and see what modifications recent 

 research has made of Laplace's original suggestion. 



In the first place, then, let us get our starting-point 

 clearly defined. A nebula has been so commonly 

 described as a " fire-mist " that most people insist on 

 conceiving it as a gigantic mass of white-hot matter, 

 thinned out far beyond the thinnest gas, and spread over 

 an incalculable space. The modern astronomer has 

 strong reason to think that a nebula need not be, and at 

 some stage probably is not, incandescent at all. We 

 believe that there are dark nebulae as well as visible 

 ones ; just as there are dark stars as well as visible ones. 

 Further, when the nebula is luminous, its light may be 

 due to electrical or radio-active conditions. Indeed, 

 there are now distinguished authorities who do not take 

 a vast outstretched gas as the starting-point of our 

 system at all. Sir Norman Lockyer has persuaded 

 many that the chaotic diffused mass, out of which our 

 sun and its planets have condensed, was a swarm of 

 innumerable meteorites those blocks of metal or stone 

 that swarm erratically in space, and so often perish 

 above us as " shooting-stars." 



More recently still a third alternative has been put 

 forward, and must be noticed here, whatever its ultimate 

 fate may be. A distinguished American student, Pro- 

 fessor Chamberlin, a geologist who claims that even 

 the earlier chapters of the earth's story fall within his 

 province, has conjectured that the diffused mass of 



