398 THE BEAUTIES OF 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 o£E, and then breaking up, formed the 

 planets and their satellites. 



