10 Nebular Theory in General 



§5. Planet esimals. 



The tidal theory, as stated by Professors Chamber- 

 lin and Moulton, postulates a sun due to the in- 

 gathering of a primal nebula. The close approach of 

 another star is supposed to draw out a secondary 

 nebula of spiral form with great rotational energy. 

 It should be borne in mind that our present-day sun 

 sometimes shoots out gaseous solar prominences to 

 heights of nearly 300,000 miles and at velocities 

 ranging up to 300 miles per second. What may it not 

 have done long ago when provoked by a passing star ! 

 It is supposed that in the arms of the secondary or 

 spiral nebula there appeared knots which condensed 

 to form the cores of the future planets. The earth- 

 moon knot is supposed to have been double. The 

 liquid or solid cores proceeded to gather in the like- 

 wise revolving outer residual material of the arms 

 and the still finer dust-like particles which Chamber- 

 lin calls planetesimals. In the case of the earth's 

 growth it is believed that the accretion of planetesi- 

 mals has been of great importance. According to 

 Chamberlin the earth was built up as a solid body, 

 not fluid or viscous after the condensation of the 

 knots into a core. 



§6. General Agreement as to the Nebular Origin of 



the Solar System. 



The cobbler should stick to his last, but we have 

 ventured, under guidance from Yale and elsewhere, 

 to enter fields beyond the domain of our personal 

 studies. For it is the purpose of these lectures to 



