8 Tidal Theory of Earth's Origin 



erine-wheel firework, would proceed to repeat the 

 process on a small scale, thus forming planets. But 

 the experts on cosmogony, like Dr. Jeans, say No. 

 The matter ejected from a giant nebula might 

 readily form more stars than we can see on a clear 

 night, but a small mass will give off only one con- 

 densation or none at all. The matter ejected from a 

 small mass might dissipate into space, or it might 

 form an atmosphere around the residual star, or it 

 might in favorable conditions form a companion star. 

 And such a binary or occasionally multiple type is 

 well known in the heavens. But it seems that a solar 

 system like ours could not arise in this way. 



§4. The Tidal Theory. 



The gist of Laplace's theory is that the solar system 

 arose by the rotational break-up of a great nebula. 

 But the difficulties in the face of this theory seem to be 

 very great, and they are not removed by starting 

 with a giant spiral nebula like those to be seen to-day, 

 which may even now be forming worlds. Thus there 

 has arisen, especially in the ingenious minds of Pro- 

 fessors Chamberlin and Moulton, a novel theory of 

 great attractiveness — the tidal hypothesis. The sun 

 and the moon raise tides on the earth to-day, and 

 there is evidence that they were once much higher. 

 It is not difficult to conceive of tides of colossal mag- 

 nitude on the sun itself. 



Similarly it is thinkable that a sun, arising per- 

 haps from the condensation of a nebula, or as a knot 

 on a spiral arm, might come to be subject to intense 



