398 THE BEAUTIES OE NATURE chap. 



ORIGIN OF THE PLANETARY SYSTEM 



The theory of the origin of the Planetary 

 System known as the " Nebular Hypothesis," 

 which was first suggested by Kant, and de- 

 veloped by Herschel and Laplace, may be 

 fairly said to have attained a high degree of 

 probability. The space now occupied by the 

 solar system is supposed to have been filled 

 by a rotating spheroid of extreme tenuity 

 and enormous heat, due perhaps to the col- 

 lision of two originally separate bodies. The 

 heat, however, having by degrees radiated 

 into space, the gas cooled and contracted 

 towards a centre, destined to become the Sun. 

 Through the action of centrifugal force the 

 gaseous matter also flattened itself at the 

 two poles, taking somewhat the form of a 

 disc. For a certain time the tendency to 

 contract, and the centrifugal force, counter- 

 balanced one another, but at length a time 

 came when the latter prevailed and the outer 

 zone detached itself from the rest of the 

 sphere. One after another similar rings were 

 thrown off, and then breaking up, formed the 

 planets and their satellites. 



