Difficulties of Nebular Hypothesis 5 



space now occupied by the solar system. As this great 

 mass lost heat into space, it contracted and its speed 

 of rotation increased. As the speed of rotation in- 

 creased, the mass would tend to become less sphere- 

 like and more lens-like. Eventually, according to 

 Laplace's suggestion, the great mass of gas would 

 cease to be able to retain its integrity. A ring or zone 

 would be separated off at the equator when the cen- 

 trifugal force of rotation got the better of the cen- 

 tripetal force of gravitation. The detached rings went 

 on revolving on their own, but under various condi- 

 tions they condensed into planets, which might again 

 project off rings like Saturn's, or satellites like 

 Jupiter's. 



§2. Difficulties of the Old Nebular Hypothesis. 



It has often been pointed out that there are lens- 

 shaped nebulae to be seen to-day in the heavens, rotat- 

 ing about an axis perpendicular to the plane of their 

 slight flattening. If these rotating masses are throw- 

 ing off material from their equatorial planes, then 

 they are behaving like Laplace's hypothetical nebula. 

 But this confirmation of the original form of the 

 Nebular Hypothesis is badly damaged by the con- 

 clusion of the experts that those apparently lenticu- 

 lar nebulas are ordinary spiral nebulae seen edgewise. 

 We are not competent to discuss the great tech- 

 nical difficulties in the way of Laplace's theory that 

 the planets arose by the rotational separation of suc- 

 cessive rings which subsequently condensed; but to 

 avoid vagueness we must mention two or three reasons 



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