174 THE OKIGltf OF OKEATIG'S, 



Second. 'Jupiter sometimes attracts a comet on its way 

 towards the sun, and delays its movements, but always repels it 

 again. None of the other planets have been, reported to 

 influence comets in any way. 



Third. Some comets, such as Halley's, Encke's and others, 

 return within a certain number of years ; but by far the greater 

 number are never again noticed or reported. 



Fourth. ~While a large number of comets have luminous 

 tails, most of them have none. 



Fifth. -Comets do not keep on one plane, nor move 

 similarly to the planets, but they appear to come from any, and 

 every direction. 



Sixth.- Sometimes a comet when it approaches the sun is 

 shot straight back again with tremendous force. This was the 

 case with one in 1680, which Sir Isaac Newton saw, and which 

 he endeavoured to explain by the law of Gravitation ; but he 

 could not account for the force which repelled it from the sun. 



The comet of 1680, Sir John Herschell says, was perhaps 

 the most magnificent one ever seen. It appeared from No- 

 vember, 1680, to March 1681. It was not very bright at 

 first, but as it approached the sun it grew more brilliant. 

 " "When, within one-sixth of its surface, it turned violently 

 round," and was shot back in exactly the opposite direction 

 with such tremendous force, that in four daya it was as far 

 distant from, the sun, as in approaching it, the comet took 

 twenty-eight days to travel the same distance. 



Seventh. Ii has not yet been ascertained whether the 

 nucleus of a comet is solid or not, but from its intense 

 brightness, it is supposed to be so. 



Thus in the motions- of- comets we have an entirely dif- 



