§14. FORMATION OF THE SOLAR SYSTEM. 45 



14. Formation of the solar system. — In accordance 

 with this hypothesis our sun is regarded as a planetary orb 



Lign. 5. — Telescopic view of encke's comet. 



with a luminous atmosphere, the central nucleus of a nebu- 

 losity which originally extended to the extreme verge of 

 our planetary system. During the condensation of this 

 nebula the planets were successively thrown off ; the most 

 distant, Neptune, being the first or most ancient, followed 

 by Uranus, Saturn, Jupiter, the five asteroids, Mars, the 

 Earth, Venus, and Mercury ; the satellites, as distinct 

 worlds, being the most recent of the whole. It is inferred, 

 that in any given state of the rotating solar mass, the outer 

 portion or ring might have its centrifugal force exactly 

 balanced by gravity ; but increased rotation would throw 

 off that ring, which might sometimes retain its figure, of 

 which we have a striking example in Saturn, and also in 

 the newly-discovered planet Neptune. This result, how- 



